PAUL SCHERRER INSTITUT

U

ISSN 1423-7296 March 2002

Scientific Report 2001 Volume I

Particles and Matter

ed. by: J. Gobrecht, H. Gäggeler, D. Herlach, K. Junker, P. Kubik, E. Meisel, A. Zehnder

CH-5232 Villigen PSI Switzerland

Telephone: +41 56 310 21 11 Telefax: + 41 56 310 21 99

http://www.psi.ch

I

I n t r o d u c t i o n i

L a b o r a t o r y f o r P a r t i c l e P h y s i c s 3

Foreword 4

Particle Physics Theory Theory (I) 5 Theory (II) 6 Theory (III) 7 Experiments A precise measurement of the n+ —» TC°e+v decay rate 8 High-momentum component of decay electrons from muonic gold 9 Measurement of the transverse polarization of positrons from the decay of polarized muons 10 A precision measurement of the positive muon lifetime using a pulsed muon beam and the \iLan detector 11 Precision measurement of singlet |xp capture in hydrogen 12 Search for a neutron electric dipole moment: status report 13 Search for time reversal violating effects in the decay of free neutrons 14 Precision determination of the charged pion mass 15 First results from the new pionic hydrogen experiment 16 Total cross sections of the pion-proton charge exchange reaction 17 Measurement of analysing powers in pion proton scattering 18 Determination of D-meson production cross sections using the HI silicon vertex detector 19 A tau trigger for CMS using the pixel detector 20

Nuclear Physics Doppler-broadening of gamma-rays following muon capture: search for scalar coupling 21 Cross section for radionuclide production relevant for accelerator driven systems 22

Atomic Physics Molecular effects in the cascade of exotic hydrogen atoms 23 High-resolution M 5-N 7 and M 4-N 6 satellite and hypersatellite x-ray spectra of metallic thorium bombarded by 24 MeV/amu oxygen ions 24

Detectors and Experimental Facilities Development work for the CMS pixel detector 25 Avalanche photodiodes for the CMS electromagnetic calorimeter 26 The x-ray detector for the muonic hydrogen lamb shift experiment 27 MuEgamma prototype timing counter tests 28 An ultracold neutron facility at PSI 29 Moderator selection for the PSI ultracold neutron source 30 Measurement of the ortho-D, concentration in the SINQ cold source 31 Mathematical model of the neutron EDM experiment 32 The magnetic environment for the neutron EDM experiment 33 The MSCB bus - a field bus tailored to particle physics experiments 34 Fully configurable data acquisition system for SINQ instruments 35

L a b o r a t o r y f o r A s t r o p h y s i c s 37

Foreword 38 Elemental abundances in stellar coronae with XMM-Newton 39 Spectroscopic coronal density measurements with XMM-Newton 40 VLBI observations of T Tauri south 41 Particle acceleration in irregular magnetic topologies 42 Test-particle simulation of the electron firehose simulation 43 Radial diffusion - cause of the relativistic electron enhancements in the outer radiation belt? 44 Browsing and processing HESSI data at the HESSI European data center 45 The status of the HESSI mission and preparation for launch 46 The HESSI aspect reconstruction 47 Simulating HESS? s response to gamma ray bursts 48 Superconducting transition edge as energy resolving photon detector 49 Single molecule detection of massive macromolecules with superconducting strip detectors 50

TABLE OF CONTENTS

II

Operating of the proton irradiation facility - concise summary 51 Radioisotopes production rate in HESSI shielding materials 52

L a b o r a t o r y f o r M u o n S p i n S p e c t r o s c o p y 53

Foreword 54

Superconductivity A study of vortex motion in type-II superconductors using muon spin rotation 55 Flux Une lattice of 3D superconductors 56 Magnetic field profile beneath the surface of Pb and Nb films 57 Low-energy |xSR investigation of the oxygen isotope effect on the magnetic penetration depth of YBa 2 Cu,0 7 8 58 Experiments on the magnetic flux line lattice in an antidot patterned niobium film using the PSI low-energy muon facility 59 Exotic anisotropic superconductors 60

Superconductivity and Magnetism Magnetic and superconductivity in 1212-type ruthenocuprates 61 Coexistence of magnestism and superconductivity in RMCe 0 6RuSr 2Cu 2O 1 0 (R = Eu and Gd) 62 Coexistence of superconductivity and antiferromagnetism in YbPd2Sn 63 Studying the magnetic instability in heavy-fermion (U,Th)Pt3 64 Magnetic-superconducting multilayers 65 Slow muon experiments on a superconductor / ferromagnet YBa,Cu 3 0 7 / SrRuO,superlattice 66

Magnetism High field nSR-measurements in the magnetic phase of the heavy fermion compound Ce 7Ni 3 67 The magnetic groundstate of the Kondo alloys CeNij Cux by [iSR 68 Field induced magnetization distibution and antiferroquadrupollar order in CeB 6 69 Study of the magnetic properties of Ce 3Pd 2 0Si 6 and CejPd^Ge^ compounds 70 HSR magnetic studies of ErB 1 2 71 Slow spin dynamics in non-Fermi-liquid UCu 5 iPd x , x = 1.0 and 1.5 72 Spin dynamics in substituted manganates 73 H+SR on ferroelectromagnetic perovskites 74 HSR study on cobalfites of type RBaCo,0 5 75 Spin fluctuations in geometrically frustrated rare earth oxides 76 Anomalous temperature dependence of the moun-spin relaxation in 5-4-10 intermetallic compounds 77 HSR studies on giant magnetoresistive Co 0 0 5 Cu 0 9 5 78 Interlayer exchange coupling in Fe/Ag/Fe studied by LE-jxSR 79 Magnetic fluctuations in ABX 3 halides 80 Muon-spin rotation and magnetization study of metal-organic magnets based on the dicyanamide anion 81 Finite size effects in single layer spin glass films studied by low energy muon spin relaxation 82 Observation of Condon domains in aluminium by j iSR spectroscopy 83

Semiconductors [iSR in II-VI solar cell materials 84 Muons in sulphur and selenium (a) 85 Muons in sulphur and selenium (b) 86 Measurement of relaxation rate and paramagnetic frequency shift of negative muon spin precession in silicon 87

Chemistry Dynamic solvent effects probed by muonium in aqueous solution 88 Local environment of cosurfactants in surfactant bilayer systems 89

Developments A combined avoided level crossing - radio-frequency resonance method 90 Low energy muon developments 91

L a b o r a t o r y f o r M i c r o a n d N a n o T e c h n o l o g y 93

Foreword 94

Nano Factory and X-ray Optics Lenses for hard x-rays with ultra-high diffraction efficiency 95 Coherence matched microfocusing of hard x-rays 96 A shearing interferometer for hard x-rays 97 Multiple beam interference lithography in the EUV and visible regions 98 Nano-structured AR-surfaces replicated by hot embossing 99 Real-time observation of electromigration induced strain in interconnect lines with imaging x-ray topography 100 Developing a toolbox for nano-replication 101

Ill

Chemical nanopatterning using hot embossing lithography 102 Transport on nanospheres in fluids 103

Silicon Based Nanomaterials and Nanoelectronics Photoluminescence and resonant tunneling of Si/SiGe quantum wells grown on relaxed 50 % / 50% SiGe virtual substrate 104 Intersubband absorption measurements performed on p-type Si/Sio.2Ge0.8 quantum wells grown on Sio.5Ge0.5 virtual substrates 105 Thermophotovoltaics - from development towards application 106 Towards SiGe low bandgap photocells grown by UHV-CVD 107 Self assembled vertical silicon quantum wells formed by the growth of Sio.gGeo.2 on patterned substrates 108 Low temperature growth of strain compensated Si/SiGe quantum wells on relaxed Sio.5Ge0.5 buffer layers 109 Shape transformation of Ge clusters on Si (100) substrates 110 Low-temperature overgrowth of Ge-clusters on Si (001) with preservation of their morphology I l l

Molecular Nanotechnology Ultrathin nanopore membranes for bioanalysis 112 Nanopatterned materials for cell adhesion studies 113 Charge transport effects in electrode coatings of streptavidin-ferrocene conjugates 114 Molecular architectures for enzyme sensors 115 A model system for the tribology and corrosion of S i 0 2 nanotowers 116 Molecular solid-gas equilibrium in two dimensions 117 Atomic force microscopy characterization of surfaces and interfaces used in catalysis, Si-Ge nanostructures, neutron mirrors and x-ray diffraction gratings 118

L a b o r a t o r y f o r R a d i o - a n d E n v i r o n m e n t a l C h e m i s t r y 119

Foreword 120

Heavy Elements Decay properties of 2 6 9 H s and evidence for the new nuclide 2 7 0 H s 121 Evidence for isomeric states in 2 6 1 R f 122 Chemical investigation of hassium (Hs, Z=108) 123 Physisorptive interaction of M e 0 4 (Me=Os, Hs) with quartz surface 124 Model studies with mercury for a future 112 experiment 125 Thermochromatographic investigation of Rh and 1 0 7 Rh with different carrier gases 126 Are thermochemical data of polonium questionable? 127

Surface Chemistry Accommodation coefficient of HOBr on deliquescent sodium bromide aerosol particles 128 Uptake of H N 0 3 to deliquescent sea salt particles 129 Aqueous phase kinetics of N 0 2 with resorcinol and dihydroxy-naphthalene 130 Uptake of N 0 2 on resorcinol and subsequent HONO formation 131 The adsorption of nitrogen oxides on ice 132 Entropy calculations of the adsorption process for NO 133 PROTRAC - Production of Tracers for Atmospheric Chemistry 134 Development of a chemical ionisation mass spectrometer 135

Analytical Chemistry Preliminary results from glacio-chemical investigation of an ice core from Belukha Glacier, Siberian Altai 136 Surface and bedrock topography of Belukha Glacier 137 First mercury determination in snow and firn from high-mountain glaciers in the Siberian Altai 138 Dating of two nearby ice cores from Illimani, Bolivia 139 Reconstruction of sublimation and precipitation from the Cerro Tapado ice core (North Chilean Andes, 30 °S) 140 Perturbation of the Chimborazo glacio-chemical record by volcanic eruption and melt water percolation 141 Search of a suitable glacier archive in the Bernina area 142 First shallow firn core records from Gorra Blanca, Patagonia 143 Melt water and nitrate release from a melting snow pack 144 THEODORE: A new sample preparation system for the M C determination in the OC and EC fraction of aerosols 145 Atmospheric 7 Be and 2 1 0 Pb activity concentrations at the high-alpine site Jungfraujoch 146 1 0 Be/ 7 Be ratios at the high-alpine site Jungfraujoch to study stratosphere-troposphere exchange 147 Application of neutron activation analysis at SINQ 148 Trace element analysis of some low and medium Z elements in ice samples by total reflection X-ray fluorescence (TXRF) 149

Cement Chemistry Cement Chemistry: Quality control and developments 2001 150 Prompt gamma-ray activation analysis of ashes from the PSI incinerator 151 Determination of the surface area of activated slag samples 152

IV

Project Radwaste Production of 53-d 7 Be from graphite waste targets 153 Efficient separation of mono-, di- and trivalent cations by high performance ion chromatography 154 Determination of uranium and plutonium in shielding concrete 155 DNA-seeking gadolinium complexes for neutron capture therapy (NCT) 156

Laboratory for Ion Beam Physics 157 Foreword 158 The PSI/ETH tandem accelerator facility 159 Measurement of plutonium isotopes with the Zurich 0.5 MV AMS system 160 Time-of-flight detection in sub-MeV accelerator mass spectrometry 161 Radiocarbon dates of old and middle Kingdom monuments in Egypt 162 Refined radiocarbon chronologies and a correlation between climatic records 163 Uses of C-14 data in a transect of Mid-Atlantic Ridge 164 Conservative behavior of 1 0 Be in water masses of the Antarctic circumpolar current 165 Paleoceanography in the North Pacific Ocean 166 Reconstruction of the Earth's magnetic field intensity over the last 200 000 years, based on 1 0 Be records in deep-sea sediments ... 167 Status of radionuclide measurements in the ice of the South Inilchek Glacier (Kyrghyzstan) 168 Reconstruction of the paleoaccumulation rate of central Greenland using Be-10 and Cl-36 169 Variability of 1 0Be and 36C1 in recent Antarctic snow and air samples 170 Exposure age of late glacial and early Holocene moraines in the Ferwall Group, Austrian Alps 171 1 0 Be exposure dates for the Birch Hill moraine system, South Island, New Zealand 172 Structure of the last glacial maximum in southern mid-latitudes: Terrestrial evidence from New Zealand 173 Reconstruction and surface exposure dating of the last ice cap in the western Alps 174 Pleistocene and Holocene glaciers advances in central Asia and Nepal as assessed by in situ cosmogenic 1 0 Be exposure ages of moraine boulders 175 Reconstructing paleo-glaciations on the Tibetan Plateau by surface exposure dating 176 Erosion studies over various spatial and temporal scales using in situ-produced cosmogenic nuclides in sediments 177 Paleo-erosion rate records from cosmogenic 1 0 Be in a 1.6 MA terrace sequence of the Meuse River, The Netherlands 178 Quantification of the effects of lithology, landscape dissection, and glaciation on rock weathering and large-scale erosion as determined by cosmogenic nuclides in river sediments 179 4 1 Ca intercomparison measurements 180 1 2 9 I and 1 2 7 I in European soils 181 Determination of 1 0 Be and 2 6 A l in meteorite Acfer 168 and a model calculation to reconstruct its size as a meteoroid 182 Investigation of platinum group elements at the Cretaceous-Tertiary boundary with accelerator SIMS 183 Selective electrodeposition of Cu nanostructures on FIB sensitised p-Si 184 Radiation hardness of CdTe/CdS solar cells under low energy proton irradiaton 185 An ExB filter for the investigation of liquid metal ion sources 186

List of publications 187

Contributions to conferences and workshops 205

Lectures and courses 233

Awards 235

1

INTRODUCTION

Progress in science has several ingredients, theoretical modelling, technological progress in experimental techniques and collection of facts in carefully done experiments. It is a chance for the transdiciplinary orientation of PSI to benefit from technological developments in one field and apply it or transfer it to other fields. We have seen a collection of such knowledge transfers accross boundaries of laboratories at PSI.

Initiated by the needs of the collider experiments at DES Y in Hamburg and CERN in Geneva we have a competent group for the development of ASIC chips combining low power analog electronics with high bandwidth digital data through­put on the same chip. The environment at the large hadron collider LHC requires in addition radiation hard technology which otherwise is only needed in space or military appli­cations. Presently the group develops a pixel detector with pixelsize of 0.15x0.15 mm and hit capability of 40 MHz. Its ultimate aim is to identify decays of heavy quarks with a finite lifetime of picoseconds. The technical knowledge aquired has been successfully transferred to a x-ray detector used at the SLS to measure the diffraction patterns in protein crystallography. Compared to conventional CCD detectors this new device has a better point spread function and can be read out much faster.

Another application is a multichannel wave form sampler chip which runs at 1 GHz and was crucial for the successfully completed precision experiment to measure the beta decay of the pion t t + —> 7 r ° e + z / e . With a branching ration of only 10~ 8 a measurement of this number to an accuracy of be­low 1 % needs a high pion stopping rate in the apparatus and hence an excellent double hit resolution of the calorimeter. The wave form digitizer easely recognizes such double hits.

Another technology driver at PSI is astrophysics. Since some time our group develops superconducting tunnel junc­tion detectors (STJ) which have a phantastic energy resolu­tion from visible light to soft x-rays. An array of such de­

tectors (pixels or strips) would advance the detection of faint sources considerably. First results could be achieved with a strip array of such detectors. Although not ready yet for applications in astrophysics, the technology could be trans­ferred to a commercial mass spectrometer which determines the mass of molecules by a time of flight technique using as detectors the STJ.

All these detectors would not find its applications with­out the technology and expertise in the laboratory for micro-and nanotechnology. It ranges from help in bump bonding, sensor production and fabrication of cooled silicon surface barrier detectors. The latter were essential in the first chemi­cal analysis of the superheavy element Hassium produced at GSI in Darmstadt. A team from the laboratory of radiochem-istry could detect a few of the Hassium atoms and determine its chemical properties.

Pixel detectors for imaging give large data volumes. This implies also a challenge to the front end electronics and the data aquisition system. Our electronics group successfully designed and commissioned the necessary electronics, espe­cially the multidetector interfaces for SINQ instruments.

In future we would like to go one step further. The high brightness at the SLS enables the imaging of fast processes on the microsecond scale. New detectors will be developed to store images on the pixel or strip at MHz speed. A video of the development of turbulence in a flame with 10 /xs frame rate or faster would be a great progress. The expertise for such a project is available and could become a challenging project for the future.

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2

3

L a b o r a t o r y fo r P a r t i c l e P h y s i c s Foreword

Particle Physics T h e o r y

E x p e r i m e n t s

Nuclear Physics

Atomic Physics

Detectors and Experimental Facilities

4

LABORATORY FOR PARTICLE PHYSICS

Kurt Gabathuler

At the beginning of 2001, two groups, both involved in fast detector readout electronics, were merged into the Labo­ratory for Particle Physics, this being the environment where the most challenging problems tend to arise, requiring so­lutions enabled only by means of very advanced tools and technologies. The new electronics group is open to all poten­tial customers within PSI. With this addition the laboratory staff has now risen to almost 50 people.

The PSI accelerators were scheduled to deliver a total of 32 weeks of beam on target, in 2001. However, due to techni­cal problems with beam shutters and collimators in two me­son beams, utilized by particle physics experiments, an un­scheduled shutdown of two weeks, in August, was necessary for repair work. We are grateful to the /xSR and SINQ com­munities for their understanding and to the operation crew for their efficient and fast repair work.

For the first time in the history of the meson beams at PSI, a single experiment has occupied one of the beam areas for an entire year. This experiment, measuring the rare decay of a charged pion into a neutral pion, t t + —> tt° + e+ + ve

(probability ~ 10~ 8 ) with a projected relative precision of 0.005, was run by a local crew of only three people. This was made possible by a highly automated data taking and detector control system, using the modern communication means available today, e.g. automatic calls of the running crew upon computer generated alarms and when possible, alarm resets via the Internet. The collaboration used an elec­tronic logbook, accessible also to the groups abroad. The groups from the U.S. were in charge of the routine controls scheduled during the night shift (early evening in the U.S.). The experiment has accumulated in excess of 50 k events so far, a 30-fold increase over previous measurements. It now remains to be seen whether the systematic errors are under control at the level of the statistical error, in which case the collection of additional events might be worthwhile.

Two of our longstanding, faithful user groups have left the scene with the retirement of their team leaders in 2001. Prof. Roland Engfer from Zürich University initiated, to­gether with Hans-Christian Walter, a series of SINDRUM experiments on forbidden muon processes and decays: SIN-DRUM started up in 1981 with the decay fi -> 3e, followed in 1988 by a new detector SINDRUM-II, to search for fi -> e conversion. The data analysis of this experiment is now al­most finished, and a new very low limit for a gold target, of around 5 x 1 0 ~ 1 3 can be expected. In 1990, the orig­inal SINDRUM detector was converted and extended for a search of muonium-antimuonium conversion (SINDRUM-I, together with Heidelberg). The stringent limits on forbidden processes, and other results on allowed rare pion and muon decays, have found their entry into the Tables of the Particle Data Group. This programme is now being continued at PSI by a new collaboration of Japanese, Italian and Swiss physi­cists proposing a very sensitive search for fi —> e + 7 .

Prof. Jiirg Lang's group from ETHZ performed a series of experiments studying weak effects in nucleón processes involving delicate polarization measurements, first at Injector I and later at SINQ, as well as other activities in precision ex­periments of ordinary muon decay, involving polarization pa­rameters. Future appointments to the above-mentioned two chairs is not forseen, which will lead to a loss of Swiss users at PSI. Fortunately, two new small groups from Geneva and Fribourg have recently joined our users community.

Prof. Peter Truöl, chairman of our experiment evalua­tion committee, has retired from the post after having served on it since 1993. He closely followed the developement of our laboratory during its re-organization, and, together with all other committee members, advised us on the approval of many new experiments, in particular fi —> e + 7 , the Ul-tracold Neutron Source and the two muon lifetime measure­ments. We will miss his outspokenness and direct statements during the user meetings and his deliberations and recom­mendations on the committee, and thank him for his valuble advice. We also thank his successor, Prof. Cyrus Hofmann, who has agreed to take on this difficult task, and wish him many stimulating discussions in the user meetings and on the committee. While in earlier days the committe was mainly concerned with the physics evaluation of new proposals and the assignment of priorities in allocating beam time to the many experiments, in the future it will have to deal rather with monitoring the progress of fewer, though longer-term experiments on a regular basis.

The planning of the new Ultracold Neutron Source (UCN) has continued in 2001, focusing on some of the most difficult aspects singled out by an ad-hoc advisory panel, e.g. beam kicker, magnetic shielding and stabilization, ortho-para con-vertion in solid deuterium and Be-coated storage vessel.

Considerable progress can be reported on our contribu­tions to the preparation of the CMS detector, which is to be installed at the Large Hadron Collider LHC at CERN. For the pixel detector, the design of the readout chip, being the most difficult part of the project, has been completed and an engi­neering run is in production. The first conceptual ideas on the readout architecture emerged some four years ago, and since then 2-3 people have been working continuously on this en­deavour. - The project of the development of the light sensors for the electromagnetic calorimeter (avalanche photo-diodes APD), for which PSI is also responsible, has passed from the R&D phase to the production phase. However, a close mon­itoring of the incoming APDs will be necessary during the production in the coming three years.

The year 2001 has also brought to light CERN's finan­cial difficulties in the completion of the construction of LHC. Hopefully, this will not lead to a long delay in the comple­tion date of the collider, which is presently planned for 2006. However, correspondingly the construction of the detectors will presumably also take more time than anticipated.

5

THEORY (I)

At present the Theory group works mainly in the follow­ing fields: exotic atoms (nuclear, atomic and molecular ef­fects), strong interaction physics at low energy, nonpertur-bative methods in field theory (variational methods, lattice gauge theory), and the Standard Model of particle physics (Higgs physics, electroweak radiative corrections) together with its supersymmetric extensions.

Below and in the following contributions a few examples are presented in more detail; for further topics see the detailed list of publications which also includes the work done in col­laboration with visitors. Among these note, in particular, the recently published textbook

Manfred Böhm, Ansgar Denner and Hans Joos: Gauge Theories of the Strong and Electroweak Interaction, B. G. Teubner (Stuttgart/LeipzigAViesbaden), 784 p. (2001).

Microscopic calculation of total ordinary muon capture rates for medium-weight and heavy nuclei

Investigating muon capture in nuclei allows the determi­nation of the coupling constants of the hadronic weak cur­rent in the nuclear environment. Of particular interest are the weak axial-vector g A and the pseudo-scalar gp coupling con­stants. It is still an open question whether g A in the nuclear medium deviates from its free value (quenching). We have therefore made a thorough theoretical calculation of the total ordinary muon capture rates for medium-weight and heavy nuclei [1]. The exclusive capture rates have been calculated for all definite final states of the product nuclei and the total rate has then been obtained by summing over all considered final states, avoiding the use of the closure approximation and the not very well defined average neutrino energy. Our calculations are based on the effective capture Hamiltonian of Morita and Fujii [2], using muon wave functions that take into account the finite size of the nuclei. The nuclear matrix elements of the capture Hamiltonian and the excited states of the product nuclei have been calculated within the quasi­particle random phase approximation, using a phenomeno­logical effective residual interaction. The results presented in Fig. 1 show for the lighter nuclei a reasonable agreement between the theoretical and experimental [3] capture rates. For the heavier nuclei like 1 4 0 Ce and 2 0 8 Pb a larger discrep­ancy between theory and experiment is observed which can

be traced back to the neutron distributions calculated with our single particle wave functions. The neutron distributions for the heavier nuclei are experimentally not very accurately known. A reduction of the theoretical neutron skin thickness leads also for the heavier nuclei to a reasonable agreement between the theoretical and experimental capture rates. All our calculations have been performed with the free values of g A and gp, indicating that there is most likely no quenching of the coupling constants in nuclei.

. 1... . 1 . . . . . . . . 1. . . . 1 . . . . ! . . . . 1 . . . . i . . . . i. *" Pb

- • Ce

o o -

- Mo .

Z r /

Sn

I •

+ S\ H -

O

A

i +

—•*+ +

1 Ni

Z fäj

25 30 35 40 45 50 55 60 65 70 75 80 85

z

Figure 1: Comparison between experimental and calculated total capture rates. Crosses: experimental data taken from [3], open and full circles: calculations with two different residual interactions, full triangles: calculation with reduced radius of the neutron distribution. The full curve connects the rates calculated with the Goulard - Primakoff formula [4] with its parameters determined from [3].

REFERENCES

[1] V. A. Kuzmin, T. V. Tetereva, K. Junker, A. A. Ovchinnikova,nucl-th/0104061, to appear in J. Phys. G 28, 665 (2002).

[2] V. V. Balashov and R. A. Eramzhyan, Atomic Energy Review Vol.5, 3(1967); IAEA, Vienna.

[3] T. Suzuki, D. F. Measday, J. P. Roalsvig, Phys. Rev. C 35, 2212(1987).

[4] B. Goulard, H. Primakoff, Phys. Rev. C 10, 2034(1974).

E. Accomando, A. Denner, S. Dürr1, Th. Jensen2, K. Junker, A. Kaiser2, V. E. Markushin3, M. Melles, H. Pichl, S. Pozzorini, R. Rosenfelder, Ch. Schwanenberger'1, M. Spira, M. Weber

1 now: DESY Zeuthen, Germany 2 PhD student

3 now: AIT Information Technology Division, PSI 4 now: DESY, Hamburg, Germany

6

THEORY (II)

Theoretical investigations of the atomic cascade in light exotic atoms

The cross sections for the scattering of muonic, pionic, kaonic and antiprotonic hydrogen in excited states from ato­mic hydrogen have been calculated in a fully quantum me­chanical framework which takes the energy shifts and, in the case of the hadronic atoms, the widths of the ns states into account [1,2].

The deexcitation of exotic hydrogen atoms in highly ex­cited states in collisions with hydrogen molecules has been studied using the classical-trajectory Monte Carlo method. The Coulomb transitions with a large change of the princi­pal quantum number n have been found to be the dominant collisional deexcitation mechanism at high n, which leads to a fast deexcitation and a significant acceleration at the initial stage of the atomic cascade [1,3]

The atomic cascades in pp and pp atoms at low density have been studied in detail. The calculated X-ray yields, ki­netic energy distributions, and cascade times are in a good agreement with the experimental data [3] (see Fig. 1).

0

0.25 eV • 1 • ' i i

0.5 eV 1 e V -

'. • - - y ^ x ' n=14

10"7 10"6 10"5 10" N/LHD

this production mechanism, the cross section has to be cal­culated at next-to-leading order in perturbation theory, since the theoretical uncertainties at leading order are too large. The QCD corrections to this Higgs production process have been determined and found to decrease the cross section at the Tevatron by about 20% and to increase the production rate at the LHC by about 20% [5]. The final result for the cross section at the LHC is shown in Fig. 2 as a function of the Higgs boson mass at leading and next-to-leading order. The residual theoretical uncertainties after including these corrections amount to about 10-15%, which is sufficient for a reliable future analysis of this process.

. ' ' ' 1 ' ' ' 1 ' ' ' 1 • • • • • • • • • • • • • • • • • • • • • • • • •

a(pp —» flH + X) [fb] Vs = 14 TeV ji = mt + Mjj/2

LO \ NLO

. . . i . . . i . . . i

" - ^ ^ ^ j

80 100 120 140 160 180 200 220 240 260 M H [GeV]

Figure 2: Production cross section of pp —> ttH at the LHC in leading and next-to-leading order with the renormalization and factorization scales set to p = mt + MH/2.

REFERENCES

Figure 1: Density dependence of the median kinetic energy of the muonic hydrogen atom at the end of the cascade. The initial conditions are: n = 14 and mean kinetic energy 0.25, 0.5 and 1.0 eV. The experimental data are from Ref. [4].

Higgs radiation off top quarks at hadron colliders

Higgs boson radiation off top quarks plays a crucial role for the Higgs search at the Tevatron and the LHC for Higgs masses below about 130 GeV. Moreover, this process pro­vides a direct way to measure the top Yukawa coupling of the Higgs particle. However, to enable a reliable analysis of

[1] T. S. Jensen and V. E. Markushin: Scattering of light exotic atoms in excited states, Hyperfine Interactions, accepted for publication (2001).

[2] V. E. Markushin and T. S. Jensen, Nucl. Phys. A 691, 318c(2001).

[3] V. E. Markushin and T. S. Jensen: Kinetics of Atomic Cascade in Light Exotic Atoms, Hyperfine Interactions, accepted for publication (2001).

[4] R. Pohl, disseration, ETH No. 14096, Zürich (2001).

[5] W. Beenakker, S. Dittmaier, M. Krämer, B. Plumper, M. Spira and P. M. Zerwas, Phys. Rev. Lett. 87, 201805 (2001).

E. Accomando, A. Denner, S. Dürr, Th. Jensen, K. Junker, A. Kaiser, V. E. Markushin, M. Melles, S. Pozzorini, R. Rosenfelder, Ch. Schwanenberger, M. Spira, M. Weber

7

THEORY (III)

Electroweak radiative corrections at high energies

Future high-energy colliders, such as the Large Hadron Collider (LHC) at CERN or a linear e + e ~ collider, will per­mit to investigate electroweak processes in the TeV-energy range with an experimental accuracy ranging from the few-percent up to the permille level. The evaluation of theoretical predictions with a corresponding level of precision requires the calculation of quantum corrections in perturbation theory.

At future high-energy colliders electroweak corrections become increasingly important since for energies far above the electroweak scale, E 3> M, they are enhanced by log­arithmic contributions of the type a™ l o g 2 " ~ m (E/M), with 0 < m < 2n — 1, where a w is the electroweak coupling and M the mass of the electroweak gauge bosons. These contri­butions, which we call electroweak logarithmic corrections (EWLC), typically lead to corrections of tens of percent at the one-loop level (n = 1) and some percent at the two-loop level (n = 2).

EWLC originate either from the running of coupling pa­rameters or from the splitting of the scattering particles into pairs of particles in the soft and/or collinear limit. In the last years we have developed a general method that permits to prove the universality of the one-loop EWLC that origi­nate from soft and/or collinear virtual splittings [1, 2]. The most important result was the proof that collinear logarithmic singularities in the spontaneously broken electroweak gauge theory factorize basically in the same way as in symmetric non-abelian gauge theories like QCD. As a consequence, this kind of EWLC is completely process-independent.

A complete analysis of all types of one-loop EWLC has been performed and simple analytical results have been made available, which include leading, subleading, and angular-dependent contributions and can be easily applied to arbi­trary electroweak processes at high-energy colliders. More­over, we analysed the numerical impact of these corrections on differential cross sections for fermion-pair- and gauge-boson-pair production at e + e ~ colliders.

We also investigated the impact of the EWLC and the ap­plicability of our method at the LHC. To this end, we per­formed a detailed phenomenological analysis for WZ and W 7 production at the LHC [3]. The corrections to the hadro-nic processes pp —» W ± 7 —» Ivij and pp —» W ± Z —» IvJ'l' have been implemented in leading-pole approxima­tion. It has been checked that in the region of large trans­verse momentum of the gauge bosons, which is particularly interesting for 'New Physics' searches, the leading-pole ap­proximation still represents a sufficiently precise approach to evaluate the corrections for the LHC if proper cuts are ap­plied. In this region, as can be seen in Fig. 1, the EWLC lower the theoretical predictions by 10-20%.

The possibility to extend our one-loop results to two-loop and higher orders has been actively investigated [4, 5 ,6] . To

1 1 1 1 1 1 1 W7 Born W7 O(a) WZ Born WZO(a)

0 0 1 1 -0.1

-0.2 *'...^* • ^

-0.3 1 1 -0.3 400 600

300 350 400 450 500 550 600 650 700 P£ut(;T', 7) [GeV]

Figure 1: Leading order and one-loop-corrected cross sec­tions for the processes pp —» W ± 7 —» Ivij and pp —» W±Z -> Ivil'V at yfs = 14TeV as a function of the cut on the transverse momentum of the photon and of the re­constructed Z boson, respectively. The inset plot shows the relative corrections.

this end, the electroweak theory has been treated, in the high-energy limit, as an effective SU(2)xU(l ) unbroken gauge theory, where the longitudinal gauge bosons are described by means of the Goldstone Boson equivalence theorem. In this picture, QCD resummation techniques can be extended to the electroweak theory and exact gauge symmetry provides fac­torization and exponentiation properties of the logarithmic corrections that originate from soft and/or collinear virtual gauge bosons.

All-order results have been presented for arbitrary elec­troweak processes, including the leading contributions of or­der an log 2 " (s/Myj) and the subleading contributions of or­der an l og 2 "" 1 (s/M^). It turned out that the two-loop sub-leading EWLC change cross sections in the percent regime at TeV energies. Their inclusion is thus mandatory for precise theoretical predictions at future e + e ~ colliders.

REFERENCES

[1] A. Denner and S. Pozzorini, Eur. Phys. J. C 18,461 (2001).

[2] A. Denner and S. Pozzorini, Eur. Phys. J. C 21, 63 (2001).

[3] E. Accomando, A. Denner and S. Pozzorini, hep-ph/0110114, to appear in Phys. Rev. D.

[4] M. Melles, hep-ph/0104232.

[5] M. Melles, hep-ph/0108221.

[6] M. Melles, Phys. Rev. D 64,014011 (2001).

E. Accomando, A. Denner, S. Dürr, Th. Jensen, K. Junker, A. Kaiser, V. E. Markushin, M. Melles, S. Pozzorini, R. Rosenfelder, Ch. Schwanenberger, M. Spira, M. Weber

8

A PRECISE MEASUREMENT OF THE T T + - > iz°e+u DECAY RATE

M. Bychkov1, E. Frlez1, W. Li1, R. C. Minehart1, D. Pocanic1, L. C. Smith1, W. A. Stephens1, B. Vandevender1, Y. Wang1, K. O. H. Ziock1, W. Berti2, Ch. Broennimann2, J. F. Crawford2, M. Daum2, R. Horisberger2, D. Renker2, S. Ritt2, R. Schnyder2,

H. P. Wirtz2, T. Kozlowski3, B. G. Ritchie4, V. A. Kalinnikov5, N. V. Khomutov5, A. S. Korenchenko5, S. M. Korenchenko5, N. P. Kravchuk5, N. A. Kuchinsky5, D. Mzhavia6, Z. Tsamalaidze6,1. Supek7

R-89-01.1, PIBETA Collaboration: VIRGINIA1 - PSI 2 - SWIERK3 - ARIZONA 4 - DUBNA 5 - TBILISI6 - ZAGREB 7

The PIBETA experiment aims to measure the pion beta decay (ir+ —> ir°e+v) branching ratio to about 0.5 % in its current phase. The best experimental value at present has er­ror limits of ~ 4 %, far exceeding the theoretical uncertainty of < 0.15%.

During 2001 we have successfully concluded "produc­tion" data taking at the ir+ stopping rate of ~ 9 x 10 5/s. The PIBETA detector system ran in the automatic mode with minimal human intervention, requiring that only two experi­menters be physically present at the PSI site, with other col­laborators working remotely.

We have also taken data at the reduced beam intensity of ~ 9 x 10 4/s, necessary for the precise determination of the absolute calibration of the measurement. Fig. 1 shows the prehminary off-line analysis of the n+ —> e+v positron en­ergy spectrum for the 1999/2000 data set, used to normalize the 7T/3 branching ratio.

1999/2000 Partial n* —> e V Analysis Results - Preliminary I Entries"

80 90

E „ (MeV)

Figure 1: Measured ir+ —> e+v energy spectrum (solid markers) and GEANT-simulated detector response (full his­togram), used for the nß beanching ratio normalization.

are being reduced in the ongoing analysis. A series of beam and equipment failures diverted much of our effort from the analysis to addressing the experimental problems, consequen­tly slowing down the progess of our data analysis, as well as reducing the 2001 event statistics well below the planned to­tal. As the experimental run finished at the end of 2001, we fully expect to make quick progress in the data analysis from this point on.

1999/2000 Partial nß Analysis Results - Preliminary

o JÜ 600 e

z 400

200

0

I Entries 2Í717

( o )

•

\ X

-

0 20 40 60 80 100 120 140

U - t « (ns)

1999/2000 Partial n* —>e'vy Analysis - Preliminary ' ' ' ' ' I Entries

Z 750 o

I 500

250

T Ï Î 7

(b ) E . t > 5 2 MeV E ,>52 MeV

T„=25.82±0.31 ns

0 20 40 60 80 100 120 140

( t . . +O/2-U (ns)

The most important result of the 2001 running period concerns the acquired event statistics. With ~ 3 0 % of the data replayed and the most stringent off-line cuts we find >20,000 clean irß events. Having studied the relaxation of the software cuts we expect eventually to recover ~ 2 0 % more data in the current sample bringing the total irß up-to-date event count to > 60,000. The irß timing spectrum is displayed in Fig. 3a.

Based on the analysis of the partial data sample to date we have extracted a preliminary irß branching ratio:

BRvß = [1.044 ± 0.007(stat) ± 0.015(sys)] x 10" 8 .

The main contributions to the systematic uncertainty, the de­tector acceptance (1.0%) and the ir —> ev lineshape (1.0%),

Figure 2: Timing spectra for -itß events [top panel, (a)] and 2-arm7T —> ev^ events [bottom panel, (b)].

In parallel with the pion beta and ir —> ev decays, we have also simultaneously recorded a large set of radiative de­cay events for the processes ir+ —> e+vy and p+ —> e+pvy. The PIBETA experiment will increase by almost two orders of magnitude the current world statistics for these processes. Fig. 2b illustrates the quality of our data by showing prelim­inary results of the partial data analysis of the radiative pion decay. Full analysis of these channels is required as a critical check of the overall experimental systematics.

This work is supported by the Russian RFBR grants, by U.S. NSF and DOE grants and PSI.

9

HIGH-MOMENTUM COMPONENT OF DECAY ELECTRONS FROM MUONIC GOLD

W. Berti2, R. Engfer 3, E. A. Hermes 3, T. Kozlowski3'*, G. Kurz 3, /. Kuth \ G. Otter \ F. Rosenbaum 2, N. M. Ryskulov 2, A. van der Schaaf3, P. Wintz 3, /• Zychor3'*

R-87-03, SINDRUM II COLLABORATION: AACHEN 1 - PSI 2 - ZÜRICH 3

In the year 2000 S I N D R U M II raised the sensitivity to neutrino-less /i-e conversion on heavy targets by two orders of magnitude. In a preliminary analysis [1] no signal was ob­served and since no further large improvements in sensitivity can be expected the experiment was stopped.

In the past year the two of us left to finish the project have focused on a better understanding of the observed elec­tron distribution which has a dominant contribution from p~ decay in orbit (MIO). Other sources of electrons, such as ra­diative muon capture followed by 7 —> e + e ~ or p~ decay in flight, have contributions of 0(%) which can be ignored. Once a good description of the observed distributions has been obtained a reliable estimate can be made of the new limit on /i-e conversion on gold.

The energy distribution of electrons from the decay of free muons at rest peaks at the kinematic endpoint m M c 2 / 2 . In muonic atoms the endpoint is raised to m M c 2 — B — R, with B: ¡JT binding energy and R: nuclear recoil energy. The energy distribution has been calculated for various cases. We use results for lead [2] correcting for the 0.54 MeV shift in endpoint energy. The yield drops to 5.15 x 10~ 7 , 5 .67 x 1 0 ~ 8

and 4.36 x 10~ 9 per stopped muon for energy thresholds of 70,75 and 80 MeV, respectively.

Detailed studies were made of: • variations of the tracking efficiency during data taking. Tracks have typically thirty anode hits and roughly half of them have cathode information as well. This single-hit cath­ode efficiency varied within a factor two, however, depending on parameters such as gas quality and chamber high voltage.

• precision of the tracking detector. The observed position resolution versus drift time was im­plemented in the event simulation.

• position of the two gold tubes used as stopping target and the distribution of muon stops over the target. As can be seen from the distributions of Fig. 1 the target was

top view

z (cm)

Figure 1: Distributions of the trajectory's point of closest ap­proach to the spectrometer axis. The target consisted of two tubes of 32 cm length each. As can be seen the downstream target had a slightly smaller diameter (38 mm, as compared to 45 mm for the upstream tube).

off centre by more than a centimetre which has a strong effect on the acceptance of the spectrometer at the low end of the

observed energy distribution. Better knowledge of the tar­get geometry also allows a better suppression of backgrounds from cosmic rays and reconstruction errors.

• the efficiency of the Cerenkov end-cap detector. For a correct description of the observed distribution of polar angle it is crucial to account for the angular dependence of the light collection efficiency.

S I N D R U M II gold2000

Figure 2: Comparison of measurement and simulation of muon decay in orbit for various kinematic quantities.

Figure 2 compares the measured energy and angle dis­tributions with the predictions from the GEANT simulation. The shape of the stop distribution along the target was ad­justed. The agreement is quite satisfactory given the 10-20% errors introduced by uncertainties in quantities such as the number of stopped muons, the value of the magnetic field, the shape of the beam profile, the trigger and selection effi­ciencies. The structure in the <p distribution reflects the shift in the target position. The dip around 6 = 90° is caused by the end-cap requirement. The drop of the event rate towards lower energies is caused by the lower threshold on tranverse momentum resulting from the cylindrical symmetry of the spectrometer. The overall efficiency varies as a function of electron energy: from « 1% around 75 MeV where the event rate has its maximum to « 10% in the region of interest for pc conversion. As a next step we will focus on that region.

REFERENCES

* permanent address: Inst, for Nucl. Studies, Swierk [1] S I N D R U M II CoUab., P S I Se i . Rep. 2000,1, 8. [2] R. Watanabe et ai,

Atom. Data and Nucl. Data Tab. 54,165 (1993).

10

MEASUREMENT OF THE TRANSVERSE POLARIZATION OF POSITRONS FROM THE DECAY OF POLARIZED MUONS

K. Bodek1,2, A. Budzanowski4, N. Danneberg1, W. Fetscher1, Ch. Hubes1, M. Janousch1, L. Jarczyk2, K. Kirch1, St. Kistryn2, J. Klement1, K. Köhler1, A. Kozela1'4, J. Lang1, M. Markiewicz1, G. Llosa1, X. Morelle3, Th. Schweizer1, J. Smyrski2,

J. Sromicki1, E. Stephan 5, A. Strzalkowskï2, J. Zejma2

R94-10.1, ETH 1 - J. U. CRACOW2 - PSI 3 - INR CRACOW4 - KATOWICE5

This experiment aims at improving present limits [1] on the transverse positron polarization by one order of magni­tude to get better limits on non-standard couplings and time reversal invariance in weak interactions.

Polarized /x + arrive in bunches every 20 ns and are stopped in a beryllium target yielding a stop rate of 2 x 1 0 7 s _ 1 . Their polarization precesses with a frequency of 50 MHz in a mag­netic field of 0.3 T. The fact that the accelerator period (20 ns) corresponds to the precession frequency (50 MHz) pre­serves the polarization of the muons. The decay positrons passing a start counter are tracked with drift chambers, and annihilate in a magnetized vacoflux foil which serves as a Polarimeter. Two additional small chambers and veto coun­ters ensure that the annihilation took place in the magnetized foil. The two annihilation photons are detected in the BGO calorimeter consisting of 127 hexagonal modules. Figure 1 shows the setup of the experiment.

Veto Counters

Drift Chambers and Return Yoke

Figure 1: Setup of the /xp T experiment. Details are given in the text and in Ref. [2].

With the introduction of the new MBS data acquisition system the event rate could be improved considerably, so that by the end of 2000 a total of 160 x 10 6 valid annihilation events has been collected.

Due to the /x-spin rotation, the effect of a transverse po­larization component will manifest itself in a rotation of the photon intensity distribution on the BGO calorimeter. This time dependence can be written in the form

f(t) = 1 + A • sin(io t + a) (1)

where to is the angular frequency of the spin precession, t is the time between a fixed phase of the RF and the decay of the

muon, and A and a are functions of the e + energy, the po­sition of the two photons and the two orthogonal transverse polarization components. Eq. (1) has been used with a subset of 11 x 10 6 events to perform a log-likelihood parameter es­timation of the two orthogonal transverse polarization com­ponents P T I and P T 2 - From their energy dependence, and assuming only one coupling in addition to the standard V-A coupling, new limits for a scalar righthanded coupling gRR

can be derived. Preliminary results are shown in Figure 2.

Figure 2: Experimental, preliminary limits for a possible righthanded scalar coupling. The big circle shows the math­ematically allowed region, the smaller circle is a limit de­rived by a general analysis of all muon decay data, and the innermost, solid circle is derived from a small subset of this experiment, assuming only one coupling in addition to the standrad V-A coupling. The insert on the lower right shows the inner region with a different scale.

This project is supported in part by the Swiss National Science Foundation, and by the Polish Committee for Scien­tific Research under Grant No. 2P03B05 111.

REFERENCES

[1] H. Burkardei al., Phys. Lett. B 160, 343 (1985).

[2] I. C. Barnett et ai, Nucl. Instrum. Meth. A 455, 329 (2000).

11

A PRECISION MEASUREMENT OF THE POSITIVE MUON LIFETIME USING A PULSED MUON BEAM AND THE ¡JLLAN DETECTOR

R. M. Carey2, T. A. Case1, D. Chitwood3, S. M. Clayton3, K. M. Crowe1, P. T. Debevec3, F. E. Gray3, K. Giovanetti4, T. Gorringe5, D. W Hertzog3, Y. Jia5, P Kammel3, B. Kiburg3, B. Lauss1,1. Logachenko2, J. Mace4, J. P. Miller2,

C. J. G. Onderwatei2, C. C. Polly3, B. L. Roberts2, A. Sharp3, S. Tripathi5, S. E. Williamson3, P. Zolnierczuk5

R-99-07, BERKELEY1 - BOSTON 2 - ILLINOIS3 - JAMES MADISON 4 - KENTUCKY 5

The goal of iiLan (Muon Lifetime ANalysis) is a 1-ppm measurement of the positive muon lifetime, r M +, resulting in a 20-fold improvement over previous efforts. This will lead to an increased precision in the determination of the Fermi constant, GF, by an equal amount. The rate of any elec­troweak process is determined by GF- Such an undertaking is challenging and in keeping with a recent trend to improve the precision of measurement of the fundamental parameters of the standard model. Until recently the extraction of from muon lifetime data has been restricted by uncertainties in the standard model theory. With modern calculations, this roadblock has been removed, and the only factor limiting fur­ther improvement is the experimental precision on the muon lifetime measurement.

In order to carry out the experiment, and to anticipate fu­ture related efforts such as high-precision Lip capture, we are designing a beamline appendage for 7rE3 and a state-of-the art decay spectrometer. The idea is to impose a time struc­ture on the 7rE3 surface muon beam by introducing a fast "kicker" similar to the successful MORE development. The new kicker parameters are being designed to transmit beam to target for 1 LIS, followed by a beam-off time of 20-50 LIS with an extinction factor aimed at better than 0.1%. During the beam-on collection period, approximately 15-20 muons will arrive on a depolarizing, solid target located at the center of a symmetric detector. The decay period, with beam off, is used to measure positrons in the 180 individual triangular-shaped scintillator pairs. The global structure of the detector was slightly modified to a 32-faced truncated icosahedron as shown in Fig. 1. The PMTs will be read out by custom 500 MHz waveform digitizers and a bank of online proces­sors will be employed to fit pulse shapes in order to deter­mine decay times. Due to the immense data volume, only a fraction of the data will be permanently stored.

Since R-99-07 was approved, we have made three short runs in 7rE3 in order to study the beam and to test prototypes of our detector and target designs. Our most recent 2001 runs were used to measure carefully beamline properties of 7rE3. In particular, a direct measurement of the phase space under a variety of slit configurations. We have also spent considerable time modelling the beam with standard tools such as Transport and Turtle and part of our beamtime was used to test various predictions of these model tunes. With the accumulated information, we are confident that a kicker design can be made in 2002 and we plan to test a mock-up kicker during our next beamtime allocation.

Based on initial studies both at PSI and at our laboratory, we have evolved the original LiLan detector design. The in­dividual detectors have proceeded through five iterations in order to optimize the lightguides and minimize their mass.

The present version exceeds specifications outlined in the proposal. The global counter geometry has been modified from an original icosahedron superstructure to the 32-sided shape shown in Fig. 1. We have conducted PMT stability tests and have identified good candidate tubes.

Specific accomplishments since the initial submission of the proposal include:

• A thorough investigation of both old and new 7rE3 tunes has been made and the phase space and muon flux have been measured as a function of horizontal and vertical slit settings.

• Sulfur and silver targets, located inside magnetic fields, were used to study the stopped muon residual polar­ization using two magnet designs. Detector prototypes were read out using waveform digitizers. Design work on the new digitizers has reached the "schematic for prototype" stage.

• A GEANT4 simulation of the experiment has been de­veloped.

• Funding for the experiment has been obtained from a U.S. National Science Foundation Major Research In­strumentation award.

• The Collaboration has been strengthened significantly with the inclusion of experienced groups from UC-Berkeley, James Madison, and Kentucky.

Figure 1: 3D view of the tiLan detector.

12

PRECISION MEASUREMENT OF SINGLET ßp CAPTURE IN HYDROGEN

V. A. Andreev1, D. V. Balin1, T. Banks3, L. Bonnet6, R. M. Carey7, T. A. Case3, D. Chitwood4, S. M. Clayton4, K. M. Crowe3, R T. Debevec4, J. Deutsch6, P. U. Dick2, A. Dijksman2, J. Egger2, D. Fahrni2, A. A. Fetisov1, S. J. Freedman3, V. A. Ganzha1,

B. Gartner3, T. Gorringe8, J. Govaerts6, F. J. Hartmann5, D. W. Hertzog4, A. Hofer2, V. I. Jatsoura1, P. Kammel4, A. G. Krivshich1, B. Lauss3, E. M. Maev1, O. E. Maev1, V. E. Markushin2, L. Meier2, D. Michotte6, C. Petitjean2, G. E. Petrov1,

R. Prieels6, S. M. Sadetsky1, G. N. Schapkin1, R. Schmidt2, G. G. Semenchuk1, M. Soroka1, A. A. Vorobyov1, N. I. Voropaev1, P. Zolnierczuk8

R-97-05, GATCHINA1 - PSI 2 - BERKELEY3 - URBANA 4 - MUNICH 5 - LOUVAIN 6 - BOSTON 7 - LEXINGTON 8

The goal of this experiment is a 1% precision measure­ment of the singlet capture rate A s in the process ßpis —> n + vß. This rate is very sensitive to the weak form fac­tors of the nucleón, in particular to the induced pseudoscalar coupling constant, gp. Its determination will constitute a rig­orous test of modern effective field theories of QCD.

Our method is based on an extremely precise measure­ment of the muon lifetime in the ß~p system (to ± 10 ppm), in comparison with that of the free ¡i+. As can then be de­termined from the difference of inverse lifetimes. The ¡i~p measurement must be performed in ultra pure and deuterium depleted hydrogen gas ("protium") to avoid any transfers of negative muons to impurities or deuterium nuclei, both of which would lead to distorted time spectra.

During the previous years, a novel time projection cham­ber (TPC) operating in 10 bar hydrogen gas and special dead-time free TDC electronics was developed, capable to track each muon to its stop location and properly identify the ß —>-e decay [1]. In March 2001 the detailed technical proposal of our final setup and apparatus was presented to the BVR and received approval from PSI.

PlPl PlP\

Figure 1: Side view of final setup. 10 bar pressure vessel (1 = 60 cm) with TPC in the center surrounded by two Sindrum chambers and two plastic hodoscopes for electron tracking.

Figure 1 presents a side view of our final setup which is now in full construction. The TPC (x-y-z = 15-12-30 cm 3 ) sits in the center of a pressure vessel filled with 10 bar ultra pure protium. Charges from tracks of ionizing particles drift toward wire planes on the bottom where they are amplified with gas gains up to ~ 1 0 4 .

Low energy muons entering the apparatus are tracked

by thin plastic triggers, two sets of wire chambers and the TPC. The pressure tank can alternatively be high vacuum baked or be pressurized by a service system which moves in on rails. The cylindrical walls are made of 4 mm aluminum.

The electron detector consists of two Sindrum wire cham­bers which were originally designed for rare decay experi­ments at PSI. Together with the plastic hodoscope surround­ing the outer wire chamber the electrons can be traced back to the muon stop region in the TPC. The lifetime of each muon is precisely determined by fast scintillators. Our system is designed to handle muon rates up to 50 kHz.

Many components of the new setup were tested in De­cember 2001 at the ¡JEA beam with very encouraging results:

• The TPC vessel was pressure tested at 15 bar and high vacuum baked to 10~ 7 mbar. A muon wire cham­ber built exclusively with high vacuum materials was mounted. The tank was filled with 10 bar purified pro­tium produced by our chemical gas handling system.

• A 37 MeV/c muon beam was stopped in the protium gas and muon signals from the hydrogen wire cham­ber were analyzed. The chambers worked with high effiency at -5.5 kV cathodes voltage. A high flux test with 2 • 106p/s during one day indicated no deteriora­tion of the chamber performance. This was achieved with a clean protium filling with impurity levels ana­lyzed to be below 10~ 7 .

• The prototype electron detector consisted of the inner wire chamber, instrumented with new anode front-end electronics mounted directly on the chamber, and a first pair of hodoscope counter elements. It was suc­cessfully operated for five days at running conditions with a 30 kHz ¡ i + beam stopping in an active scintil­lator target placed in a 50 Gauss magnetic field. The statistics collected will allow studying the muon life­time and /LtSR effects on the ~ 3 0 ppm level.

• New electronic devices were tested during these runs (i.e. fast deadtime free CAEN TDC's, waveform dig­itizers, data compressors) and successfully integrated into our VME based data acquisition system. Suitable analysis software for the new systems was developed.

In summer 2002 a commissioning run of the full setup and in fall 2002 a first production run are scheduled.

REFERENCES

[1] PSI Ann. Rep. Annex 1,1997; 1998; 1999; 2000, p.32,20,15,13; http://www.npl.uiuc.edu/exp/mucapture; P. Kammel et al., Nucl. Phys. A 663 ;664,911c (2000).

13

SEARCH FOR A NEUTRON ELECTRIC DIPOLE MOMENT: STATUS REPORT

E. Alexandrov6, M. Balabas6, G. Bison3, K. Bodek3, M. Daum2, A. Dovator6, A. Fomin1, P. Geltenbort5, R. Henneck2, S. Kalinin1, K. Kirch2,1. Krasnoshokova1, M. Lasakov1, V. Marchenkov1, A. Murashkin1, A. Pazgalev6,1. Potapov1,

M. Sazhin1, U. Schmidt7, A. Serebrov2, G. Shmelev1,1. Shoka1, R. Taldaev1, V. Varlamov1, A. Vasiliev1, A. Weis3, N. Yakobson6

R-00-05, PNPI 1 - PSI 2 - FRIBOURG3 - CRACOW4 - ILL 5 - ST. PETERSBURG6 - HEIDELBERG7

The sensitivity goal of the new search[ 1] for the neutron elec­tric dipole moment dn at the PSI ultracold neutron (UCN) source is ~ 5 • 1 0 _ 2 8 e c m , i.e. ~100 times better than the present best result. A nonzero result for d„ within this sensi­tivity may be expected from Supersymmetry models describ­ing the Baryon asymmetry of the universe. The experiment uses the Ramsey resonance method where polarized UCN precess in a magnetic field. If d„ ^ 0, interaction with an electric field will cause a tiny energy change (~ 1 0 ~ 2 2 eV for d n = 1 0 _ 2 6 e c m ) and thus a frequency shift. The latter leads to a shift of the precession angle and is detected as a change in polarization.

IS 9 13

Figure 1: Scheme of spectrometer: (1,1') UCN detectors, (2) polar­ization analyzer, (3,13) UCN valve, (4) four-layer magnetic shielding, (5,9) HV electrode, (6) channel for Cs magne­tometers, (7) radio frequency coils, (8) Be-coated insulator, (10) vacuum chamber with magnetic field coils, (11) polar­izer, (12) neutral chamber (1 out of 5), (14) neutron guide.

The basic unit of the spectrometer (see Fig.l) is the "dif­ferential chamber pair", which allows to extract dn from a simultaneous measurement with opposite electric field, as­suming the magnetic field to be identical and stable. We have four differential chambers, surrounded by "neutral" cham­bers without electric field that serve for normalization and to study systematic effects. Magnetic field data are provided by 16 Cs magnetometers surrounding the whole setup (4 in each

of the 4 channels, see Fig.l). The resonance shift will be measured simultaneously for both spin directions with de­tectors 1, 1'. The whole setup is surrounded by a Helmholtz coil system which serves to compensate for variations of the ambient magnetic field[2].

Figure 2: Design of EDM spectrometer.

In Ref. [ 1 ] , we have derived the expected statistical uncer­tainty, assuming 2 mA proton beam on a lead target and an average density of 1000 n/cm 3 in the spectrometer. Given the volume of the 4 differential chambers (~1601), the statistical uncertainty over two 600 s long periods with reversed elec­tric fields is ödn R ¡ 4 1 0 _ 2 6 e c m . The multi-chamber system including neutral chambers and the simultaneous measure­ment of both spin directions was developed for the purpose to investigate and suppress systematic effects, e.g. (a) effects due to 1st order spatial variations of the magnetic field along the chamber axis are eliminated, while those from higher or­der variations are strongly reduced, (b) effects due to leakage currents in the HV chambers are reduced, (c) effects due to UCN density fluctuations are reduced. We have made ex­tensive simulations to study the reduction performance with respect to (a) and (b) and find suppression factors of ~ 5 and ~ 7 , respectively [3].

REFERENCES [1] A. Fomin et al., PSI Prop. R-00-05,

and A.P. Serebrov et al., PSI Prop. R-00-05.2, available from http://ucn.web.psi.cn/.

[2] K. Bodek et al., this Scientific Report (R-00-05.2). [3] M. Daum et al., this Scientific Report (R-00-05.1).

14

SEARCH FOR TIME REVERSAL VIOLATING EFFECTS IN THE DECAY OF FREE NEUTRONS

M. Beck4, K. Bodek1, A. Czarneckf, W. Fetscher2, W. Haeberli8, C. Hubes2, K. Kirch3, St. Kistryn1, A. Kozela2'9, J. Plaut1'3, P. Schuurmans4, A. Serebwv6, N. Severijns4, J. Swmicki2, E. Stephan5 and J. Zejma1

R-96-04, JU-CRACOW1 - ETH-ZÜRICH2 - PSI 3 - CU-LEUVEN 4 - US-KATOWICE5 - PNPI-GATCHINA6 -UA-EDMONTON 7, UW-MADISON 8, IFJ - CRACOW9

An experiment aiming at the simultaneous determination of both components of the transversal polarization of elec­trons emitted in the decay of free, polarized neutrons is un­derway at the cold neutron facility FUNSPIN at the spalla­tion source SINQ, PSI, Villigen. A non-zero value of the component PTI , which is perpendicular to the plane spanned by the neutron polarization and the electron momentum, would signal Time Reversal Violation (TRV) and thus physics be­yond the Standard Model. The component Pn conserves time symmetry and is finite in the Standard Model. Its value will serve for an internal calibration of the apparatus and cross check of systematic uncertainties. We estimate that an experiment with the absolute accuracy of 0.005 is feasible within a few weeks of data taking time. This will be the first such measurement for the decay of free neutrons bear­ing a potential to detect a non-standard value or to provide important constraints for the scalar and tensor couplings in the semileptonic weak interactions.

A dedicated polarized neutron beam fine has been fin­ished at SINQ, Sector 50. Detailed measurements of the beam properties including the neutron flux distribution, the divergence, and the wavelength dependence of neutron po­larization have been performed [1].

Neutron Beam Wire Chamber

Scintillator Hodoscope

Scattering Foil

Figure 1 : Mott Polarimeter for electrons from the decay of slow neutrons.

Large angle Mott scattering will be used for the deter­mination of the transverse electron polarization. The corre­sponding angles will be determined from the electron tracks measured by a low-mass MWPC as sketched in Fig. 1. Track­ing of electrons also helps to discriminate the Mott scattering events from severe background due to the capture of slow neutrons in the apparatus. Using a small prototype detector [2] a signal-to-background ratio of 2:1 has been measured (Fig. 2). Further improvements are still possible. Based on the results from extensive laboratory and in-beam tests with the prototype MWPC, a full size (50 x 50 cm 2 ) detecting system consisting of one MWPC and one scintillator wall has been designed and built. The detector is equipped with

a new generation of readout and trigger electronics (Fig. 3). The commissioning of this new system has been started in December 2001 and the data taken is being analyzed. They will be completed by a performance test, for which a mea­surement of the neutron Decay parameter A is planned.

800 700 600

¡2 500 uno; 400 300 200 100 0

-Decay ß-Spectrum

^Theory

30 600 E[keV]

R - n f e a

Figure 2: Energy distribution of electrons from neutron de­cay measured with a small prototype detector. The solid line is predicted by theory and includes corrections for energy losses.

Figure 3: View of the new detecting system installed in the FUNSPIN area. Neutron decay chamber is partially dis­mounted.

REFERENCES

[1] Ch. Hilbes, Ph. D. Thesis, ETH, (2001), unpublished.

[2] K. Bodek et al., Nucí. Instr. Meth. A 473, 326 (2001).

15

PRECISION DETERMINATION OF THE CHARGED PION MASS

D. F. Anagnostopoulos1, G. Borchert2, J.-P. Egger3, D. Gotta2, M. Hennebach2, P. Indelicato4, Y.-W. Liu5, B. Manil4, N. Nelms6, L. M. Simons5

R-97-02, IOANINNA 1 - JÜLICH2 - NEUCHATEL3 - PARIS4 - PSI 5 - LEICESTER6

The mass of the negatively charged pion has been mea­sured with pionic atom X-ray transitions by using a new cal­ibration method. The experiment uses the fact that the muon mass is known to an accuracy of 0.05ppm [1]. Energies of the (5^1) transitions in pionic nitrogen and muonic oxygen are 4.055 and 4.023 keV and, hence, differ by only 32 eV. This allows the simultaneous measurement of both lines with a reflection-type crystal spectrometer. Such a set-up reduces substantially the sources for systematic errors arising from instabilities during long measuring periods.

Nitrogen and oxygen targets are used in gaseous form, which leads to a well pronounced X-ray cascade. The line yield of the (5^1) transitions is about 40% and most of the in­tensity is collected in the circular transitions (5g-Af) (Figurel). In gases, screening effects from remaining electrons are neg­ligibly small thus avoiding systematic uncertainties caused by the use of solid targets [2].

i £

O m

•t í ^ 'S

55

100 200 300 400 500 600 pixel à 40 \im

Figure 1: Simultaneously recorded reflections of the pio­nic oxygen and nitrogen (5^1) transitions measured with an O2/N2 gas mixture. The Bragg angles are 52.8 and 53.4 de­grees, respectively. One channel corresponds to 2 CCD pix­els of 40 Lim or 102meV.

The pion beam of the 7rE5 area at PSI was injected into the new cyclotron trap. The gap between the magnet coils of the new trap is almost a factor of 2 wider than the one of the previously used device. This allows to stop about one order of magnitude more muons which stem from the decay of slow pions inside the trap. However, the low count rate for muons is one of the limiting factors of the experiment. In the set-up optimized for pions up to 250 X-rays per hour were achieved for the 7rN(5^1) transition.

The second limitation originates from a large Doppler broadening of the 7rN and liO transitions due to Coulomb explosion. The acceleration of the charged ions during the

separation of the molecules - for the first time directly ob­served by this experiment [3] - doubles the line widths as expected from the spectrometer resolution of 500 meV. Con­sequently, a factor of 4 higher statistics is required to achieve the same accuracy for the line positions.

X-rays emitted from the target were reflected in second order by a spherically bent silicon crystal cut along the 110 plane. For a bending radius of 3 m, the liO and nlS reflections are separated by 25 mm. They were measured in a large area X-ray detector built up of six 25 mm x 25 mm CCD chips set up for this experiment [4]. The gaps between the chips were determined from a mask with high precision slits and irradiated with 2.3 keV sulphur X-rays excited in a target at about 4 m distance by means of an X-ray tube.

For the simultaneous measurement an oxygen/nitrogen gas mixture of 90%/10% at 1.4 bar was used yielding a count rate of 15 per hour both for the liO and the nlS (5g-Af) transi­tion. More than 8000 events were recorded in each of the cir­cular transitions. The error for the value of the pion mass is dominated by statistics for the measurement with the 0 2 / N 2

gas mixture. It amounts to 1.7ppm for 75% of the total statis­tics analyzed up to now. The systematic contributions to the error are small. From the curvature of the reflections an un­certainty of ± O.lppm arises. Temperature and bending cor­rections are both of the order of 0. lppm only because of the small difference of the Bragg angles. The uncertainty stem­ming from the determination of the gaps between the CCDs with the slit mask is at present 0.5ppm, but will be negligible after a remeasurement with improved statistics.

A second energy calibration has been performed for con­sistency reasons by using the copper fluorescence radiation. The method follows the line as described in our preliminary experiment of the pion mass [5]. An accuracy of about 2ppm is expected here.

To summarize, the pion mass has been remeasured by comparing the wavelengths of pionic and muonic X-ray tran­sitions. Finally we expect an accuracy of about 1.5ppm for the new determination of the pion mass. The final value will be available after a precise calibration of the spectrometer dispersion early in 2002.

REFERENCES

[1] D. E. Groom et al. (PDG), Eur. Phys. J. C 15 ,1 (2000).

[2] B. Jeckelmann, P. F. A. Goudsmit, H. J. Leisi, Phys. Lett. B 335, 326 (1994).

[3] T. Siems et al., Phys. Rev. Lett. 84,4573 (2000).

[4] N. Nelms et al., to be publ. in Nucl. Instrum. Meth. A .

[5] S. Lenz et al., Phys. Lett. B 416, 50 (1998).

16

FIRST RESULTS FROM THE NEW PIONIC HYDROGEN EXPERIMENT

D. F. Anagnostopoulos1, W. Breunlich2, H. Fuhrmann2, D. Gotta3, A. Gruber2, M. Hennebach3, P. Indelicate*, Y.-W. Liu5, B. Manil4, V. Markushin5, N. Nelms6, A. J. Rusi El Hassanf', L. M. Simons5, H. Zmeskal2

R-98-01, IOANINNA 1 - VIENNA 2 - JÜLICH3 - PARIS4 - PSI 5 - LEICESTER6 - TANGER7

The new pionic hydrogen experiment [1] at PSI aims at a substantial improvement in the determination of the isospin separated values for the scattering lengths in the pion nu­cleón system. The scattering lengths can be extracted from a measurement of the strong interaction shift and width of the ground state of the pionic hydrogen atom. This requires a high resolution spectroscopy of the corresponding X-rays, which can be performed using Bragg reflection crystal spec­trometry. Compared to the previous experiment [2] a drastic improvement in luminosity and in background suppression could be achieved with a completely newly designed exper­imental set-up. The final goal of the experiment is a deter­mination of the strong interaction width with a factor of five improved accuracy which also implies a drastic improvement of the shift value.

The experiment has started in spring 2001 with a detailed study of the pressure dependence of the ground-state shift in the pionic hydrogen atom. The aim of these measurements is to identify or exclude molecular effects which could falsify the shift value attributed to the strong interaction. Molecular effects on level energies may come from excited 7rp systems bound into complex structures forming [ (7rpp)p]ee molecules [3]. Radiative decay from such states could lead to reduced X-ray energies. Also the width measurement could be af­fected as transitions from molecular vibrational states would be Doppler broadened.

c h a n n e l

Figure 1: 7rH(3p-ls) transition measured at a pressure of 28 bar with a peak-to-background ratio of 40 to 1 at a count rate of 15 per hour for the hydrogen line. One channel correponds to one pixel of the CCD of 40 pm or 72 meV.

Only rough estimates for the formation rates exist at present and though deexcitation is expected to occur dominantly by Auger emission. Even low-intensity satellites can cause a center-of-gravity shift of the line that is noticable at the en­

visaged accuracy of the experiment. The abovementioned effects are not only influencing strongly the experiment pre­sented here but are also decisive in planning the muonic hy­drogen experiment at PSI (R-98-03). In this context a work­shop organized in November 2001 at PSI played an important role in giving new insights into the dynamics of de-excitation processes in exotic hydrogen atoms.

The 7rH(3p-ls) transition (Figure 1) was measured in the pressure range equivalent to 4 bar up to liquid by using a cryogenic target. The measurements were performed with a spherically bent quartz crystal cut along the 10-1 plane. For the first time pionic hydrogen X-rays had been observed from liquid hydrogen.

At low density the energy calibration line ir16 O (6h—5g), which is not affected by the strong interaction, was mea­sured simultaneously with the 7rH line [1]. At higher hy­drogen densities the measurement was performed alternately with pure hydrogen gas and a mixture of helium and oxygen (80%/20%) at higher temperature. Helium is needed to re­duce self absorption of the X-rays in oxygen. The oxygen fraction itself was a mixture of 1 6 0 and 1 8 0 , which allowed to check the angular dispersion of the crystal spectrometer.

The spectrometer response was determined from the ( 5 -4) line of 7 r C formed with CH\. In contrast to irO transitions pionic atoms formed with these molecules are not Doppler broadened by Coulomb explosion [4].

No pressure dependence was found for the energy of the nH(3p — Is) transitions indicating that on the present level of accuracy the molecular formation does neither impede the shift nor the width measurement. Preliminary results for the hadronic ground-state shift are 7.111 ± 3 2 ± 5meV, 7.104 ± 2 0 ±40meV, and 7.100 ± 2 5 ± 15meV for the 3 den­sities equivalent to pressures of 3.5 bar, 28.5 bar, and LH2. The first error is due to statistics, the second one accounts for calibration and alignment of the CCDs. These values are in agreement with the value of the previous experiment per­formed at 15 bar equivalent density [2]. The intensities and the peak/background ratios presently reached are the basis for future measurements aiming especially at an improve­ment of the value for the width. A first step in this direction will be undertaken in summer 2002 with the goal to reach at least a factor of two improvement.

REFERENCES

[1] PSI exp. R-98.01; http://pihydrogen.web.psi.ch

[2] H.-Ch. Schröder et al., Eur. Phys. C 21,473 (2001).

[3] S. Jonseil et al., Phys. Rev. A 59, 3440 (1999).

[4] T. Siems et al., Phys. Rev. Lett. 84,4573 (2000).

17

TOTAL CROSS SECTIONS OF THE PION-PROTON CHARGE EXCHANGE REACTION

E. Friedman1, M. Bauer2, J. Breitschopf, H. Clement2, M. Cröni2, H. Denz2, P. Jesinger2, R. Meier2, P. Vergien2, G. J. Wagner2

R-00-01, JERUSALEM1 - TÜBINGEN 2

The mass difference of up- and down-quark is the ori­gin of isospin violation in the strong interaction. The pion-nucleon system offers several possibilities for measuring the size of the violation and thus provides information on the un­derlying mechanism [1].

In pion-proton scattering, isospin breaking has been in­vestigated by using three experimentally accessible reactions: elastic scattering 7 r ± p —> 7 r ± p and single charge exchange (SCX) ir~p —> 7T°n. If isospin is conserved, the amplitudes for these reactions are connected by a triangle relation.

4 a. a- — A * ^-TT^p—y 7T~<~p ^-TT p—Y7T p

•^•TT-p—¥7T°n

The violation of this relation for s-wave at low energies has been tested by several groups, leading to contradictory re­sults. While analyses by Gibbs et al. [2] and Matsinos [3] showed large isospin violation of about 7%, a recent work by Fettes and Meißner lead to just 0.7% [1].

The conclusions from these analyses are severely affected by the small amount of data for the SCX reaction, which is not able to sufficiently restrict the calculations. To get a more reliable access to the size of isospin violation in the hadronic interaction, more data on SCX cross sections and polariza­tion observables are needed.

R00-01 measures SCX total cross sections in the energy range from 30 to 250 MeV, with emphasis on the energy re­gion below 100 MeV. Here, isospin breaking in s-wave as large as 7% should lead to a 10% deviation of the SCX total cross section from the expectation based on elastic scattering and isospin symmetry. Existing measurements do not have the precision needed for identifying this effect. This will be possible with the data from this experiment, which aims for a 2% overall accuracy.

The direct measurement of the total cross section of the SCX-reaction employs a transmission technique, which was also used in former experiments [4, 5] at A-resonance en­ergies. A small 4ir box detector consisting of thin plastic scintillators has been constructed. Incoming negative pions are counted in three small beam defining counters and hit a polyethylene target of very well known dimensions and chemical composition. The measured quantity is the disap­pearance of incoming beam particles in the detector, i. e. the probability for a final state consisting of neutral particles only. The total cross section for the reaction n~p —> 7r°n is then derived from the transmissions of the polyethylene tar­get, a carbon background target and empty target. Different target thicknesses are used. An automatic target changing system allows frequent variations of the target type. All de­tector ADC s and TDCs are being read out for every beam event at rates of up to 20kHz. Corrections have to be applied for the detection of neutrals in the detector, the 7r° Dalitz de­

cay, pion decay and radiative pion capture. The total size of the corrections is about 7%.

A very sensitive test of the whole detector is the use of positively instead of negatively charged pions in the incom­ing beam. This must lead to a zero total cross section when analyzed in the same way as the ir~ data.

In a first beam time on the 7rMl beam line, data have been taken for energies between Tv- = 6 0 and 250 MeV. The second part of the experiment will be performed in the 7rE3 area and should provide data from 90 down to 30 MeV.

Figure 1: View of the SCXBOX detector. The box sides consist of thin plastic scintillator. They are each read out by two photomultipliers. Negative pions enter through a hole in the front detector and interact in a solid target placed inside the box. If an SCX event occurs, the neutral particles of the final state (one neutron and two photons from the decay of the neutral pion) leave the box undetected.

REFERENCES

[1] N. Fettes, U. G. Meißner, Phys. Rev. C 63,045201 (2001); hep-ph/0101030.

[2] W. R. Gibbs, Li Ai and W. B. Kaufmann, Phys. Rev. Lett. 74, 3740 (1995).

[3] E. Matsinos, Phys. Rev. C 56, 3014(1997).

[4] D. V Bugg et al., Nucl. Phys. B 26,588(1971).

[5] E. Friedman et al., Phys. Lett. B 302,18(1993).

18

MEASUREMENT OF ANALYZING POWERS IN PION PROTON SCATTERING

R. Meier1, B. van den Brandt2, R. Bilger1, J. Breitschopf, H. Clement1, J. Comfort5, M. Cröni1, H. Denz1, K Fohl4, E. Friedman6, J. Gräter1, R Hautle2, G. J. Hofman3, R Jesinger1, J. A. Konter2, S. Mango2, M. Pavan3, J. Pätzold1,

G. J. Wagner1, F. von Wrochem1

R-97-01, TÜBINGEN 1 - PSI 2 - TRIUMF3 - EDINBURGH 4 - ARIZONA 5 - JERUSALEM6

From 7 rp scattering observables, important quantities of the strong interaction can be extracted: the 7 r N N coupling constant, the sigma-term of the proton and the size of isospin breaking.

Presently, there is no agreement on the value of any of these quantities [1]. This is at least partly due to the sta­tus of the 7 rp data base, in particular at low energies. There are regions where information is still missing, and there are regions where the available experimental data are contradic­tory. New measurements of 7 rp observables at low energies are aimed at providing additional information and resolving the discrepancies.

In this experiment we want to determine analyzing pow­ers in 7 T ± p elastic scattering at energies below 90 MeV. Only one data set at one energy has been available in this region so far [2]. The new data will provide important constraints for the phase shift analyses and can also be used to identify incorrect cross section data sets.

The measurement was performed at the pion beamline 7rE3 using the Low Energy Pion Spectrometer LEPS and a newly developed polarized scintillator target [3].

Pions with well defined momentum were scattered from protons polarized perpendicular to the scattering plane. The pion detector LEPS measured relative cross sections depend­ing on angle and polarization.

The target sample, a block of 18*18*5 mm 3 scintillating organic polymer, doped with TEMPO free radicals was dy­namically polarized in a field of 2.5 T in a vertical 3He-4He dilution refrigerator. A 19 mm diameter plastic light guide transported the scintillation light from the sample in the mix­ing chamber to a photomultiplier outside the cryostat. In a polarized target setup many nuclei other than protons are al­ways present in the beam interaction region. This gave rise to background for 7 rp elastic scattering which however could be sufficiently suppressed by using the active target light in­formation. The light signal caused by a throughgoing particle depends on the particle type and energy, therefore on the type of the reaction in the target. For example, the light output of a recoil proton is much higher than that of a recoil carbon nucleus or a throughgoing pion. Owing to the different light output it is possible to separate 7 rp scattering events in the tar­get from other reactions by applying cuts on the target ADC spectra (Fig. 1).

For the calculation of the analyzing power, several inde­pendent runs at different polarizations p were taken at each setting of energy and angle. As cuts on the target ADC are used for background reduction, a calibration of this ADC is required. This is done using the simultaneously measured counting rate for pion carbon elastic scattering which is in­dependent of the proton polarization.

Figure 1: Focal plane spectra from LEPS with increasing cuts on the target ADC. The peak from 7 rp elastic scattering is marked. The background is almost completely removed by requiring higher and higher thresholds on the target ADC (left to right).

Analyzing powers A y are finally calculated from the mea­sured relative cross sections in a straight line fit using the linear relation

<7p = <T 0 (1 +My). In this experiment analyzing powers were measured for

7T+p at pion kinetic energies of 45, 51, 57, 68, 77 and 87 MeV in the angular range from 40° to 120° and for 7 r~p at 67 and 87 MeV between 51° and 78°.

Preliminary results show agreement of data and phase shift predictions at the highest energies. However, signifi­cant differences develop towards lower energies.

Data taking for the experiment is finished. The analysis should be completed in 2002.

REFERENCES

[1] M. E. Sainio, irN Newsletter 15,156 (1999). U. G. Meißner, wN Newsletter 15,127 (1999). M. Knecht, irN Newsletter 15,108 (1999).

[2] R. Wieser et al., Phys. Rev. C 54,1930 (1996).

[3] B. van den Brandt et al., Nucl. Instrum. Meth. A 446, 592 (2000).

19

DETERMINATION OF D-MESON PRODUCTION CROSS SECTIONS USING THE

HI SILICON VERTEX DETECTOR

R. Eichler2, W. Erdmann2, K. Gabathuler1, J. Gassner1, C. Grab2, R. Horisberger1, B. List2

E -93-01, SWISS HI CENTRAL SILICON TRACKER COLLABORATION, PSI 1 - ETHZ 2

Perturbative quantum chromodynamics (QCD) allows the calculation of processes at a reasonably large energy scale, however only on the partonic level. Empirical models have then to be invoked to describe the formation of colorless ob­jects in the final state, i.e. hadrons. The parameters of such models, being sensitive to the actual hadronisation processes themselves, were measured among others by the LEP experi­ments. Due to the principle of factorisation these parameters are expected to be universal. This proclaimed universality can be tested at HERA by studying the charmed meson pro­duction, where different charmed final states are compared with each other in terms of production rate and distributions.

HI has previously published studies of D* and D° pro­duction. The present analysis concentrates on new decay channels of D-mesons. Exploiting the high-precision track­ing capabilities of the Central Silicon Tracker (CST), sec­ondary decay vertices from the decay of D-mesons have been measured in the channels Ds —>• $7r —>• (KK)it, D+ —» Ktttt, D° ->• Kit and D* ->• D°ir ->• (Ktt)tt. To exem­plify the quality of the signal events, fig. 1 shows the invari­ant mass distribution of the Kitit daughter candidates from a D+ decay after requiring a CST lifetime tag.

The essential feature in the analysis to establish a clear signal and distinguish it from background processes was the strict quality requirement on the vertex separation. The cru­cial variable is the significance = d/a(d), where d is the 3-dimensional vertex separation distance of the D de­cay point (secondary vertex) from the primary ep-interaction point, projected onto the r — (f> flight direction of the D-meson, and a(d) is its error.

The visible D+ production cross section has been mea­sured to be a{ep ->• eD+ X) = (3.38 ± 0.59(stat) ± 0.76(syst)) nb for the kinematical range 2 < Q2 < 100 GeV 2 ,0 .05 < y < 0 .7 ,p T (D+) > 2 GeV/cand | r](D+) \< 1.5. The predicted value based on a leading-order simulation (AROMA LO) is 3.7 nb.

A preliminary differential cross section in this visible kine­matical range as a function of the D+ transverse momentum is extracted and presented in fig.2. The shaded band indicates the model dependent uncertainties, which are not included in the total systematic errors of the data points. The comparison of the predicted shapes with the leading-order QCD simula­tion is in reasonable agreement.

The extraction of the distributions for the other decay channels (Ds, D°,D*) are still in progress, however the Sd resolution distribution is identical for all these various final states. Based on the extracted differential distributions for D+,DS,D°,D* the cross section ratio's will be available. Thus the fragmentation fractions c —>• D for D-mesons can be extracted and then be compared to expectations, based on empirical models or measurements at e+e~- and other ma­chines.

— 1 4 0 -i

> 1 2 0 H >

Pi 1 0 0 -

I 8 0

¡2 * 6 0 ^

1 .7 1 . 7 5 1 .8 1 . 8 5 1 .9 1 . 9 5 2 2 . 0 5

m ( K T O t ) [ G e V / c 2 ]

Figure 1: Invariant mass distribution of Knit candidate combi­nations, originating from a D+ —>• •kKK decay. The candidates were required to have a decay vertex separated from the ep colli­sion point.

— 10 - i o >

Ü

* 1

T3

10 -

D + -> KK V • HI (e + p 99/00) H AROMA (LO)

3 4 i I i i i i I i i i i I

5 6 7 p t (D + ) [GeV/c]

Figure 2: Differential production cross section in a visible kine­matical range for D+ —> -kKK decay candidates as a function of the D+ transverse momentum; data (solid dots) and MC simulation (line); the error bars indicate statistical and total error, where statis­tical and systematic errors have been added quadratically. The band represents the uncertainties due to model dependencies.

20

A TAU TRIGGER FOR CMS USING THE PIXEL DETECTOR

D. Kotlinski1, A. Nikitenko2,

E-94-09, PSI 1 - IMPERIAL COLLEGE - ITEP 2

Last year we reported [1] the development of an algo­rithm which uses pixel hits to reconstruct all charged tracks above a momentum threshold of IGeV/c and finds all pri­mary interaction vertices (PV). Once track candidates are found, they can be used to select (trigger) interesting events and to suppress backgrounds. Events with a high momentum lepton (e.g. r lepton) are of particular interest.

Here we present a "pixel" trigger which is used to select events with r leptons decaying hadronicaly into jets. The r-jets consist of 1, 3 or 5 charged tracks and are usually very narrow. The main background, "simple" QCD jets generated at a much higher rate, are typically much wider. Therefore the "pixel" trigger is based on an isolation criterion. The r-jet selection method is schematically shown in Fig 1. The

details about the algorithm and the event samples used in the simulationcan be found in Ref. [2].

The algorithm works very well at low luminosity. At high luminosity, however, it's efficiency becomes small (about 50%) due to the large number of tracks originating from the pile-up interactions. The efficiency is improved by using the PV information. The vertex of the leading track is assumed to be the "signal" PV (this assumption is correct for 99% of events). Once the "signal" PV is defined only those tracks which were assigned to it are considered in the isolation cri­teria. This approach increases the efficiency of our algorithm at high luminosity to the same value as at low luminosity. The variation of the QCD 2-jet background and the Higgs

mymî mm R

x °-9

¡ | 0.85

I 0.8

I 0.75 o 0.7 (5 §0 .65 10

§ 0.6

§0 .55

0.5

i il

I 1 1 1 H

cone i

:±fc cone i

V t ó \

: -M * f 'SigtTü

è • Hí( jgs 20( GeV 1 ¿ • Hí<

. . . . ¡ . . . . jgs 50C »GeV 1

. . . . ¡ . . . . . . . . i . . .

0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 e(QCD bkg.)

Figure 2: The variation of the QCD background and the Higgs signal efficiency with the isolation cone size (0.20, 0.30, 0.35, 0.40, 0.50) for Higgs mass 200GeV (squares) and 500GeV (circles) and for two values of the signal cone size 0.05 (full marks) and 0.10 (open marks).

Figure 1: A sketch showing the basic principle of the pixel r-jet identification algorithm.

r-jet direction is defined by the calorimeter trigger. All track candidates in the matching cone Rm around the jet direction and above the cut are considered in the search for signal tracks, that is tracks which originate from the hadronic r de­cay. The track with the highest pt is declared the "leading" track (tri in Fig. 1). Any other track which is in the nar­row cone Rs around tri is also assumed to come from the r decay. A larger area i?¿ is now searched for tracks above a p\ cut. If no tracks are found in the R¡ cone, except the ones which are already in the Rs cone, the isolation crite­rion is fulfilled and the jet is labeled as a r-jet. The narrow signal cone Rs around the "leading" track tri is needed in order to trigger on 3 and 5 prong r decays in addition to 1 prong. Typical values of the cuts used above are : i? s=0.05, ñ m = 0 . 1 0 , Ri=0.35,p¡ = 3GeV/c andpj = IGeV/c. More

signal efficiency with the change of the isolation cone size is shown in Fig. 2 for Higgs mass of 200GeV (full squares) and 500GeV (full circles) and for two signal cone sizes i? s=0.05 and 0.10. The points from left to right correspond to the following values of ñ¿ = 0.50, 0.40, 0.35, 0.30 and 0.20. One can see that a rejection factor of 5 (for the 0.10 signal cone) can be reached with an efficiency ~ 75%. A higher background rejection of 10 (for the 0.05 signal cone) can be achieved but at a price of the efficiency being dependent on the Higgs mass.

REFERENCES

[1] M. Barbero et al, PSI Sei. Rep. 2000,1, 25.

[2] D. Kotlinski, R. Kinnunen and A. Nikitenko, CMS Note 2001/017.

21

DOPPLER-BROADENING OF GAMMA-RAYS FOLLOWING MUON CAPTURE: SEARCH FOR SCALAR COUPLING

Yu. Shitov1, V. Egowvls, Ch. Briançon2, V. Brudanin1, J. Deutsch3, T. Filipova1, C. Petitjean4, R. Prieels3, T. Siiskonen5, J. Suhonen5, Ts. Vylov1, V. Wiaux3,1. Yutlandov1, Sh. Zaparov1

R-97-03, JINR1 - CSNSM 2 - UCL 3 - PSI 4 - JYFL5

In the Standard Model (SM) all weak interaction pro­cesses are of the V-A type. Although there is strong experi­mental evidence for the V-A form of the charged weak cur­rent, the possible admixture of genuine scalar (S) and tensor (T) type interactions cannot be excluded and — as a matter of fact — is even present in most scenarios for physics be­yond the SM, such as leptoquarks or R-parity violating inter­actions in supersymmetry. In principle, charged Higgs par­ticles could also induce such a coupling. As a consequence, considerable efforts were undertaken in the beta-decay sector to search the possible effects, which could signal deviations from the SM.

The present work extends the search of the genuine scalar interaction on the muonic sector. Here the genuine scalar coupling Cs could be different and even enhanced and would contribute to various observable quantities in muon capture summed with the induced scalar coupling: (Cs + gs)-

The investigated reaction (Fig. 1) is a two-step process which consists in the first-forbidden transition of ordinary muon capture (OMC) in a zero-spin nucleus followed by 7 -emission from the excited recoiling daughter nucleus.

27% 73% 397.27 7276.85 298.22

— 7298.22

120.42 7397.27 7I2O.42

0

3.9 ps 91.3 ps

5.25 ßs

OMC

16 N 76129

16 O Figure 1: Muon capture on 1 6 0 and decay scheme.

Using the method based on the Doppler effect and de­veloped in our previous works [1], one can investigate the correlation between the momenta q and k of the neutrino and the 7-quantum. In this case the shape of the Doppler-broadened 7-line (Fig. 2) is determined by the convolution of the detector response function (calibrated with a reference 1 6 9 Y b source) and the correlation function W which can be approximated by

W= l + 4 - P 2 ( k q ) , (1)

where P2 (cos 0) is a Legendre polynomial. The correlation coefficient a\ depends on the relative values of the nuclear matrix elements (NME) and the Weak Interaction couplings.

In order to reduce the slowing-down of the recoil nuclei in the target material, a low density target - oxygen gas at (1-16) bar pressure - was used. After 3-week test [2] in 1997 and 3-week measurement in 1998, the following correlation

14000-

12000-

10000-

6000-

6000-

4 0 0 0 -

2000

r 261.079 ( 1 6 9 Y b ) 307.738 ( 1 6 9 Yb)-

i 272.105 ( 1 7 3 L u )

/iX(Fe)

Energy, keV 266 280 28B 270 276 200 200 200 300 306 310

Figure 2: A portion of the delayed 7-spectrum, including the line-of-interest, as well as two un-broadened reference Unes.

coefficient value has been [3] obtained:

a\ = 0.096 ± 0.020 . (2)

To transform this model-independent value to the Scalar cou­pling (Fig. 3), we used the NME calculated with three differ­ent residual interactions: ZBMI, REWIL and ZWM. All of them lead to the similar (Cs + gs)^ 0 - l n order to confirm or to disprove such non-trivial result, it is planned to repeat the experiment with other target nuclei.

-0.35 -0.30 -0.25 -0.20 -0.15 -0.10 -0.05 0.00 ( C s + gs)

Figure 3: Transformation of the correlation coefficient a\ to the (Cs + gs) value.

REFERENCES

[1] Ch. Briançon et ai, Nucl. Phys. A 671,647 (2000).

[2] V. Egorov et al., PSI-experiment R97-03, PSI Nuclear and Particle Physics Newsletter 30, (1997).

[3] Yu. Shitov et al., to be published in Nucl. Phys. A 699,601 (2002).

22

CROSS SECTIONS FOR RADIONUCLIDE PRODUCTION RELEVANT FOR ACCELERATOR

DRIVEN SYSTEMS

J. Kuhnhenn1, U. Herpers1, W. Glasser2, R. Michel2, R W. Kubik3, M. Suter4

Z-97-01, KÖLN 1 - HANNOVER 2 - PSI 3 - ETH ZÜRICH4

Investigations of residual nuclide production by proton-induced reactions with with heavy target elements (73 < Z < 83) were continued with irradiation experiments up to 71 MeV at the injector cyclotron of PSI. These experiments are part of a project to measure integral cross sections for the production of residual nuclide by proton-induced reac­tions from thresholds up to 2.6 GeV for a wide variety of target elements. To obtain complete excitation functions, we combined experiments at various accelerators: LNS/Saclay (Ep = 200 - 2600 MeV), PSI/Villigen (Ep < 71 MeV), and TSL/Uppsala (Ep = 70 - 180 MeV). The goals of this project are to provide a reliable data set for the modeling of cosmic ray interactions with matter and to satisfy some of the data needs of accelerator driven transmutation of nuclear waste (ADTW) [1] and accelerator driven energy amplifica­tion (ADEA) [2]. The experiments at PSI complete the pre­viously measured excitation functions [3] to lower energies. Examples are given in Fig. 1.

The results obtained by our collaboration over more than twenty years represent the worldwide largest consistent data set of cross sections for residual nuclide production by proton-induced reactions. The entire data set for the target elements C, N, O, Mg, Al, Si, Ti, V, Mn, Fe, Co, Ni, Cu, Rb, Sr, Y, Zr, Nb, Mo, Rh, Ag, In, Te, Ba, Ta, W, Re, Ir, Au, Pb, and Bi covers nearly 1000 target/product combinations and contains about 22,000 cross sections. For a comprehensive survey on earlier work see [4]. With respect to the investigations rele­vant for ADTW and ADEA, final results are available only for target element lead [3]. For the other target elements only preliminary data were reported so far [5] - [7].

In spite of these efforts, it will not be possible to measure all relevant nuclear reaction data needed to evaluate the feasi­bility of ADTW and ADEA technologies. Consequently, one will have to rely widely on theoretical model calculations. The quality of current nuclear reaction models and codes is, however, not sufficient to predict residual nuclide production with sufficient accuracy [8]. To improve this situation fur­ther experimental and theoretical work is needed covering radionuclide production and all other aspects of medium-energy nuclear reactions. A first step to such an approach was the EC concerted action Physical Aspects of Lead as a Neutron Producing Target for Transmutation Devices. In this European collaboration a complete and reliable experi­mental data base of all relevant nuclear reaction data for the target element lead was established [9]. It is extended by the 5th framework EC project HINDAS: High and Intermediate Energy Nuclear Data for Accelerator Driven Systems.

REFERENCES

[1] Bowman et al., Nucl. Instrum. Meth. A 320, 336 (1992).

1 10

\ ! ' 'TMS '' b' '< :

M —x— " [3] •

THIS i • i ^Pb(p,xn)Bi-204 [3] , , \

i i I

/ Pb(p,39pxn)Ru-103 i. •

/ 1

Í :

Proton Energy [MeV]

Figure 1: Excitation functions for the production of 103Ru and 204Bi from from lead [9]. For earlier work see Gloris et al. [3] and references therein.

[2] F. Carminati et al., Report CERN/AT/93-47(ET) (1993).

[3] M. Gloris et al., Nucl. Instrum. Meth. A 463,593 (2001).

[4] R. Michel et al., Nucl. Instrum. Meth. B 129,153 (1997).

[5] M. Gloris et al., in: Progress Report on Nuclear Data Re­search in the Federal Republic of Germany for the Period April 1, 1997 to March 31, 1998, NEA/NSC/DOC(98) 7, INDC(Ger)-044, Jiil-3550,27 (1998).

[6] J. Protoschill et al., in: Progress Report on Nuclear Data Research in the Federal Republic of Germany for the Period April 1, 1998 to March 31, 1999, NEA/NSC/DOC(99) 10, INDC(Ger)-045, Jiil-3660,26 (1999).

[7] J. Kuhnhenn, Dissertation, University Köln, (2001).

[8] R. Michel, P. Nagel, NSC/DOC(97)-l , NEA/ OECD, Paris (1997).

[9] J.-P. Meulders et al., Physical aspects of lead as a neu­tron producing target for accelerator transmutation de­vices, Final report of an EU Concerted Action, European Communities, Luxembourg, 2001, ISBN 92-894-1237-2.

23

MOLECULAR EFFECTS IN THE CASCADE OF EXOTIC HYDROGEN ATOMS

H. Daniel1, F. J. Hartmann1, P. Hauser3, T. S. Jensen3'4, F. Kottmann2, V. E. Markushin3, M. Mühlbauer1, C. Petitjean3, R. Pohl2'3, W. Schott1, D. Taqqu3

R-97-04, TU MÜNCHEN 1 - ETH ZÜRICH 2 - PSI 3 - UNI ZÜRICH 4

The distribution of kinetic energies of exotic hydrogen atoms (/xp, 7 rp ...) at low n-levels depends not only on the initial formation of such atoms in a highly excited state, but also on subsequent acceleration in collision-induced deexci-tations and deceleration by elastic collisions during the cas­cade. A detailed understanding of these complex processes is for example important for the analysis of the measurement of the strong interaction shift and width of 7 rp atoms [1]. The population of metastable /xp(2S) atoms, which is the basis for the muonic Lamb shift experiment at PSI, also depends on the kinetic energy [2].

The kinetic energies of /xp(lS) atoms were investigated at low gas densities using a time-of-flight technique[3]. The results are summarized in Fig. 1. The measured distribu­tions extend from a fraction of an eV up to several tens of eV, depending on gas pressure. The median energy increases steadily from 0.40 ± 0.07 eV at 0.06 hPa to 2.63 ± 0.17 eV at 16 hPa. This pronounced pressure dependence demon­strates the importance of collision-induced accelerating cas­cade processes. The data at 0.06 hPa are mainly sensitive to the kinetic energies at formation of the muonic atom. At higher densities Coulomb-deexcitation (i.e. transformation of excitation energy of the /xp atom into kinetic energy of the collision partners /xp and H 2 ) become more and more im­portant, in particular at high n-states. Cross sections for the collisional processes were calculated recently by Jensen and Markushin [4] using a quantum mechanical close-coupling method for low n states and a classical-trajectory Monte Carlo method for high n. These cross sections were used in a new cascade code which reproduces the data much better than any previous calculation (Fig. 1). The agreement

0.06 mbar 0.25 mbar 1 mbar 4 mbar 16 mbar

T ( e V )

Figure 1: Integrated kinetic energy distributions W(T) = JQ p(T')dT' of the /xp atom at the end of the cascade. The points refer to our measurements whereas the lines are the results of a cascade calculation [4] starting at n = 14 with a mean kinetic energy of 0.5 eV.

between calculation and data will be further improved in near future by a more elaborate selection of the initial n- and T-values.

The data can not be reproduced without taking into ac­count molecular effects in the cascade calculations. The early stage of the cascade is dominated by Coulomb deexcitations with An = 2 — 4 and the corresponding increase in ki­netic energy, in contrast to the atomic case where An = 1 is favoured (see Fig. 2). Molecular cascade effects were the topic of a Workshop at PSI in Nov. 2001. The main problem to be resolved is the treatment of molecular effects at low n-levels where the classical method fails.

Molecular effects play an important role also in the life­time of the metastable 2S state in muonic hydrogen. Our ob­servation of high-energetic (900 eV) /xp(lS) atoms could be attributed to the quenching of long-lived /xp(2S) atoms. This first observation of long-lived /xp(2S) atoms is the crucial prerequisite for our new experiment to measure the Lamb shift in muonic hydrogen (R98-03). Both population and lifetime of the 2S state are sufficient for the Lamb shift mea­surement.

13

Figure 2: Calculated Coulomb deexcitation cross sections for np(m=l3, Eiab=l eV) scattering from atomic and molecular hydrogen as a function of the final state n / [4]. The semiclas-sical calculation of Bracci and Fiorentini is shown, too [5].

REFERENCES

[1] http://pihydrogen.web.psi.ch

[2] R. Pohl et al., Hyperfine Interactions 127,161 (2000), andR. Pohl, Ph. D. thesis, ETHZ (2001).

[3] F. Kottmann et al., Hyperfine Interactions 119, 3 (1999).

[4] T. S. Jensen and V. E. Markushin in Proc. of the pCFOl conference in Shimoda, Japan, Hyperfine Interactions, in press.

[5] L. Bracci, G. Fiorentini, Nuovo Cim. 43 A, 9 (1978).

24

HIGH-RESOLUTION M 5 - N r AND M 4 - N 6 SATELLITE AND HYPERSATELLITE X-RAY SPECTRA OF METALLIC THORIUM BOMBARDED BY 24 MeV/amu OXYGEN IONS

J.-Cl. Dousse1, D. Banas2, M. Berset1, D. Chmielewska3, M. Czarnotd2, J. Hoszowska4, Y.-P. Maillard1, O. Mauron1, T. Mukoyama5, M. Pajek2, M. Polasik6, P.-A. Raboud1, J. Rzadkiewicz3, andZ. Sujkowski3

Z-01-03, FRIBOURG1 - KIELCE2, - SWIERK3 - ESRF 4 - OSAKA 5 - TORUN 6

The experiment Z-01-03 was undertaken with the aim of investigating the multiple L-, M- and N-shell ionization induced in heavy elements by impact with fast heavy ions. High-resolution L7, Ma and Mß x-ray spectra of metallic Th and U targets were measured. The L7 spectra were observed with the Fribourg DuMond transmission-type bent crystal spectrometer installed at the beam-line NE-B. The Ma and Mß spectra whose energies are of the order of 3 keV were measured with a reflection-type bent crystal spectrometer. The latter was installed at the beam-line NE-A, upstream from the OPTIS facility. The present paper is focused on the Th M x-ray data which were collected in May 2001.

The target consisted of a 15 mg/cm 2 metallic foil of nat­ural thorium. The latter was bombarded with 376 MeV 0 7 +

ions. The average beam intensity was about 100 nA. The target M x-ray emission was measured with a von Hamos reflecting-type spectrometer equipped for this experiment with a 100-mm high x 50-mm wide x 0.2-mm thick (110) quartz crystal bent cylindrically to a radius of 25.4 cm. The target was viewed by the crystal through a narrow tantalum slit. The x-rays reflected by the crystal were measured with a 1024 x 256 pixels position sensitive CCD detector, having a depletion depth of 50 /xm and a pixel-size of 27 /xm. With the employed crystal and slit width of 0.2 mm, the instru­mental resolution was about 1 eV.

large number of components is due to the different subshells in which the spectator vacancies can be located and to the numerous ways the two holes can be coupled in the initial and final atomic states.

S s

3.050 3.100

Energy [keV]

Figure 1: High-resolution Ma, ß x-ray spectrum of thorium bombarded by 376 MeV oxygen ions.

The measured high-resolution Th Ma, ß x-ray spectrum is presented in Fig. 1. The structures occurring on the high-energy flanks of the M 5 - N 7 and M 4 - N 6 transitions corre­spond to N-satellites i.e. to x-rays associated with the radia­tive decay of M^N^1 double-vacancy states. The excess of intensity observed around 3050 eV is due to M ¿ " 1 M ~ 1 —>

N^~1Mj~1 hypersatellite transitions (i.e. to transitions with two M-shell holes in the initial state). The experimental spec­trum is compared to theoretical spectra constructed from DF (Dirac-Fock) and MCDF (Multiconfiguration Dirac-Fock) cal­culations, assuming a binomial distribution for the satellites. As shown in Fig. 1, a satisfactory agreement with the MCDF predictions is found. The energy shift of about 10 eV ob­served between the experimental data and the MCDF predic­tions for the M-hypersatellites (see inset of Fig. 1) can be explained by the fact that additional N-shell ionization was not considered in the hypersatellite simulations. Results of MCDF calculations for the M 5 - N 6 j 7 transition with, respec­tively, no spectator hole and one spectator hole in the O-, N-, or M-shell are depicted in Fig. 2 where one can see that satel­lite and hypersatellite lines consist of many components. The

MCDF calculations

3000 3020 3040 3060 3080 3100

Energy (eV)

Figure 2: MCDF theoretical shapes of the Th M 5 - N 6 > 7 dia­gram, satellite and hypersatellite lines.

25

DEVELOPMENT WORK FOR THE CMS PIXEL DETECTOR

C. Amsler3, M. Barbero4'1, R. Baur1, W. Berti1, G. Dietrich1, R. Eichler1, W. Erdmann2, K. Gabathuler1, R. Horisberger1, H. Chr. Kästli1, R. Kaufmann3'1, D. Kotlinski1, B. Meier2, Ch. Regenfus3, J. Rothe1, P. Riedler3, T. Rohe1, R. Schnyder1,

S. Streuli2, L. Tauscher4

E -94 -09 , Swiss CMS P I X E L C O L L A B O R A T I O N PSI 1 - E T H Z 2 - Z Ü R I C H 3 - B A S E L 4

The tracking unit of the CMS experiment at the Large Hadron Collider (LHC) will in its innermost part contain hy­brid silicon pixel detectors for track reconstruction and b-tagging. The Swiss CMS pixel collaboration is committed to the construction of the three barrels which will be 53 cm long and placed at radii of 4.4 cm, 7.3 cm, and 10.2 cm. They cover an area of 0.73 m 2 composed of 720 modules. The in­ner two layers containing about half of the modules must be provided at startup of CMS while the outermost layer will be introduced later when LHC reaches its final luminosity.

The year 2001 was still dedicated to R&D work on the single components. Most prominent are the readout chip and the sensor which are the focus of this report.

Readout Chip

A prototype readout chip (PSI 41) in radiation-hard DMILL technology was received and tested (fig. 1). The chip con­tains about half the number of pixel cells foreseen for the final chip but features the complete readout architecture with the complex and flexible scheme of data buffering, time stamp­ing, trigger verification and event building needed for the LHC environment. The chip was tested in detail with all features working well. The readout speed was limited to 15 MHz instead of the required 40 MHz. The sources of this limitation were identified and fixed in the final chip design. Some variants of the analog block under consideration have been analyzed. The circuit chosen requires one external sup­ply voltage less with a reduced power budget than previous versions.

The experience gained in the test of PSI 41 was used for an improved design of the final readout chip (PSI 43) which has been submitted in December 2001. This chip contains the full array of 52 x 53 pixels with an area of 150 x 150 urn 2. A control and interface block containing the programming in­terface and voltage regulation (missing in PSI 41) was added. The total chip circuit dimensions are 7.89 x 10.80 m m 2 and the total transistor count is 430410. The delivery of the wafers is expected for spring 2002.

In 2002 the translation of the readout chip into a radiation-tolerant design in a standard deep sub-micron CMOS tech­nology is planned allowing a further reduction of the pixel size to 100 x 150 \ira2. This would provide additional safety margin to obtain the targeted spatial resolution over the com­plete radiation scenario in CMS.

Sensor

In 1999 prototype sensors for the CMS pixel detector us­ing the on «" approach were successfully fabricated and tested in 2000 and 2001.

A new feature of the sensors was the implementation of a resistive network by openings in the p-stop isolation. Those resistors formed by the electron accumulation layer have been investigated in detail. They prove to be suitable for acceptance tests on wafer level if a design with only one p-stop ring was used. After irradiation-induced type inversion the value of the inter-pixel resistance was for all pixel de­signs too high to hold accidentally unconnected pixels close to ground potential. However, no correlation between miss­ing bump bonds and noisy pixel cells has been observed in ir­radiated samples. The voltage breakdown around 300 V after irradiation seems to be a more general problem of the p-stop isolation technique as observed also by other groups. The capacitance of a single pixel cell has been measured using a special routing chip bump-bonded to a sensor. The result of 25.7 ± 1.8 fF is lower than expected but within the limits of theoretical calculations. This gives more design freedom for future sensor designs. Several approaches to further im­prove the behaviour have been implemented in a new sensor prototyping submitted in Sep. 2001.

Module Construction

Crucial for the hybrid pixel approach is the bump bond and flip chip technique. Further system aspects connected to the construction of pixel modules have been studied in 2001, in close collaboration with the SLS group that successfully fabricated several pixel modules for the PILATUS-project. Both pixel groups will benefit from the common experience in many respects. Examples are the bump bonding technique itself, yield optimization in the bump bonding process and the high density interconnect technology and design.

Figure 1: Photograph of a PSI 41 chip mounted on a test board. Its size is 6.2 x 8.3 m m 2

26

AVALANCHE PHOTODIODES FOR THE CMS ELECTROMAGNETIC CALORIMETER

Z Antunovic1, K. Deiters2, N. Godinovic1, Q. Ingram2, Y. Musienko3'5, P.Poerschke2, D.Renker2, S.Reucroft3, R. Rusack4, T. Sakhelashvili2, A. Singovski4,1. Soric1, J. Swain3, P. Vikas4

1 Univ. Split, Croatia 2 Paul Scherrer Institute, Villigen, Switzerland

3 Northeastern Univ., Boston, USA 4 Univ. of Minnesota, Minneapolis, USA

5 on leave from INR (Moscow)

CMS is one of the two main general purpose detectors being built for LHC, the l5TeV p-p collider at CERN. The main physics goal of the LHC is to find the Higgs particle, whose mass is now predicted to be close to the lower limit of 115GeV set by present experimental results. At masses below 150GeV one of the best detection channels is the de­cay into two photons, and this is the primary design goal of the Electromagnetic Calorimeter (ECAL). To observe this the ECAL must have good energy resolution. Photons are converted in scintillating lead tungstate crystals, of which there will be 61,200 in the barrel part of the detector. The light emitted by each crystal, proportional to the energy de­posited, is measured with a pair of Avalanche Photodiodes (APDs) [ 1 ]. These have been developed by Hamamatsu Pho­tonics especially for this purpose over 8 years of R&D in collaboration with PSI and other CMS ECAL institutes.

The requirements for the APDs include operation in a 4 T field, survival under irradiation of 2 . 1 0 1 3 n / c m 2 and 2.5kGray, speed (lOnsec), and compatibility with the de­manding energy resolution requirements. The latter implies large area, good sensitivity to light around 430 nm, 99.9% re­liability over the 10 years expected operation and low noise and dark current. Lead tungstate allows a very compact calo­rimeter but has a low light yield which brings in two fur­ther important requirements: gain and insensitivity to ionis­ing particles traversing the diode [2] . . . [6]. The APDs devel­oped for CMS are silicon photodiodes operated in avalanche mode to provide gain (x 50 will be used).

Once the R&D appeared to have achieved these demand­ing requirements PSI placed a contract for their supply and APD deliveries started in early 2000. After some time it be­came clear that they were not as radiation hard, nor as stable in accelerated ageing tests, as had been indicated by the pro­totypes, and a production pause was introduced to address these difficulties. Radiation hardness proved to be very hard to assure, and is affected by a number of details. One impor­tant indicator of radiation hardness was found to be the dis­tance between the breakdown and operating voltages. This is now over 40V (see Fig. 1) for the bulk of the production (which also means that the APDs can be operated at gains of over 1000, where they still perform stably).

After some changes to reduce lateral and surface fields deliveries were resumed in early 2001. It was also decided that all APDs must undergo screening with 5kGray of Cobalt irradiation (carried out in the PSI gamma irradiation facility in the Hot Lab) followed by combined annealing and acceler­ated ageing in an oven. Special investigations of approaching 1000 APDs has indicated that these screening procedures are

a reliable identifier of bad or weak APDs. By the end of 2001 some 15% of the total have been delivered with the produc­tion building up to around 5000 per month.

Error bar shows range within delivery

date of delivery

Figure 1: Mean and spread in distance between breakdown and operating voltage for APD deliveries from March 1999 until July 2001. The error bars indicate the range within each delivery.

REFERENCES

[1] The CMS Electromagnetic Calorimeter Project Techni­cal Design Report, CERN/LHCC 97-33 (1997)

[2] K. Deiters et al., Nucí. Instrum. Meth. A 442,193 (2000).

[3] K. Deiters et al., Nucí. Instrum. Meth. A 453,223 (2000).

[4] K. Deiters et al., Nucí. Instrum. Meth. A 461,574 (2001).

[5] K. Deiters et al. Published in Cracow 2000, Electronics for LHC experiments, 221-225.

[6] Q. Ingram et al. Proceedings of the European Physi­cal Society International Conference on High Energy Physics, Budapest, July 2001.

27

THE X-RAY DETECTOR FOR THE MUONIC HYDROGEN LAMB SHD7T EXPERIMENT

A. Antognini4, F. Biraben1, M. Boucher3, C. A. N. Conde2, S. Dhawan6, L. M. P. Fernandez2, T. W. Hänsch4, F. J. Hartmann5, V.-W. Hughes6, O. Huot3, P. Indelicate1, L. Julien1, P. Knowles3, F. Kottmann8S, Y.-W. Liu10, L. Ludhova3, F. Mülhausen, F. Nez1, R. Pohl4'7, P. Rabinowitz9, J. M. F. dos Santos2, L. Schallet3, H. Schneuwly3, W. Schott5, J-T. Shy10, D. Taqqu7,

J. F. C. A. Veloso2

R-98-03, PARIS1 - COIMBRA 2 - FRIBOURG3 - MPQ MUNICH 4 - TU MUNICH 5 - YALE 6 - PSI 7 - ETHZ 8

PRINCETON9 - HSINCHU TAIWAN 1 0

An experiment is being prepared at PSI to determine the Lamb shift (25 — 2P energy difference) in muonic hydrogen and to deduce the rms proton charge radius with 1 0 ~ 3 rel­ative accuracy. A sufficiently high population of long-lived /xp(2S) atoms was established by the direct observation of a non-radiative 25-decay channel [1]. A new beam line for low energy negative muons was developed and tested suc­cessfully [2] which is adapted to the needs of the Lamb shift experiment. The muons have to be stopped in a small volume (20 x 1.5 x 0.5 cm 3 , 2 hPa H 2 ) surrounded on two sides by mirrors of a laser cavity and on the other two sides by detec­tors for the Lip(n = 2 —> 1) 1.9 keV x-rays. The target is mounted in a 5 Tesla axial magnetic field which is part of the beam assembly and provides a transversally small muon stop distribution. The high magnetic field restricts the choice for x-ray detectors.

Extensive computer simulations of the laser mirror cavity were carried out during 2001. The arrangement of the mir­rors with cylindrical bends was optimized in several steps, resulting in an optically stable configuration with relatively low requirements for mechanical tolerances. A particular ad­vantage of the new solution is that the x-ray detectors can be mounted very near the muon stop volume. A set of commer­cially available large-area avalanche photo diodes (LAAPD) with 16 mm active diameter can therefore be used as detector for the 2 keV x-rays [3]. The detection efficiency is essen­tially given by the solid angle and reaches nearly 20%.

800

E n e r g y [ k e V ]

Figure 1: Energy spectrum measured with LAAPD (16 mm active diameter) irradiated by 2.3 keV x-rays from sulphur fluorescence. The small peak at 5.9 keV originates from backscattered x-rays of the 5 5 Fe source used to excite the sulphur target. Electronic noise becomes dominant below 1 keV.

The operation of LAAPDs as 2 keV detectors in a mag­netic field up to 5 Tesla was tested recently. Fig. 1 shows a typical energy spectrum for 2.3 keV fluorescence x-rays from a sulphur target irradiated by 5.9 keV x-rays. The en­ergy resolution of 30% (FWHM) obtained at 2.3 keV can still be improved by careful optimization of the preamplifier and shaping amplifier parameters. A time resolution below 30 ns was measured with a 5 4 M n source.

The dependence of the LAAPD output on the magnetic field is shown in Fig. 2. There is essentially no drop of the amplitude for irradiation by x-rays and visible light which both have a relatively large penetration depth in the diode, whereas the independence is quite significant for uv pho­tons (170 nm, produced by a Xe gas proportional scintillation chamber) which are absorbed very near the entrance dead layer of the diode.

0 1 2 3 4 5 magnetic field (T)

Figure 2: Relative amplitude of the LAAPD versus magnetic field, for irradiation by visible light (~500 nm), 5.9 keV x-rays from a 5 5 F e source, and VUV light from xenon scintil­lation (170 nm).

REFERENCES

[1] H. Daniel et al., PSI Sei. Rep. 2000,1, 23; R. Pohl, Ph. D. thesis ETH Zürich (2001).

[2] F. Biraben et al., PSI Sei. Rep. 2000,1,28.

[3] M. Moszynski et al., Nucl. Instrum. Meth. A 442,230 (2000).

28

MUEGAMMA PROTOTYPE TIMING COUNTER TESTS

R-99-05, MuEGamma Collaboration : BINP NOVOSIBIRSk - ICEPP TOKYO - INFN PISA - IPNS KEK NAGOYA - PSI - WASEDA

The aim of the MuEGamma experiment is to search for the lepton-flavour violating decay it —¥ ej to a sensitiv­ity of ~ 1 0 ~ 1 4 , more than two orders of magnitude lower than the current search Hmit set by the MEGA-experiment at LAMPF [1]. In order to achieve this goal, a detector capable of handling the intense surface muon rate, produced by the 7TE5 beam at PSI, and able to resolve the positron and pho­ton from the decay with the best possible momentum/energy-, positional- and timing-resolutions, is required.

The main detector components, are shown in Fig.1. Sur­face muons of 28 MeV/c enter the thin-coil, superconducting solenoid and are stopped in a small, thin target. The subse­quent decay of the muon leads to a Michel positron, which exhibits a spiral path with increasing pitch, the bending ra­dius of which depends entirely on its total momentum and is 'independent' of its emission angle. These novel features are achieved by the gradient field of the solenoid magnet, with a maximum field strength of 1.27 T at the centre of the de­tector and decreasing axially. The positron momentum and angle are determined by tracking the particle with a set of azimuthally spaced, staggered-cell drift chambers, while the energy, timing and angle of the photon are obtained from a liquid Xenon calorimeter, viewed from all sides by some 800 photomultiplier tubes. The timing of the positron and hence the trigger condition for coincident back-to-back decay prod­ucts, is given by a set of fast, double-layered, orthogonally placed, scintillator timing-counter arrays, positioned at op­posite ends of the detector.

Xe Scintillation Detector

Thin Superconducting Coil / \^ j

Muon Beam ' Stopping Target

Timing Counter

1m

Figure 1 : Plan View of the MuEgamma Detector showing the main components, as well as an example of the decay trajectories of the positron and photon.

Several timing-counter prototypes were built and tested at the cosmic ray test facility CORTES at INFN Pisa. The results reported below are for a (100 x 5 x 1) cm3 Bicron 404 scintillator bar, wrapped with 50 pm of aluminized Mylar foil and coupled to Philips XP2020 UR photomultiplier tubes (PMTs) at either end. Tests were also done with Hamamatsu R5946 fine mesh tubes and variously shaped light guides.

The CORTES facility consists of a set of cosmic trig­ger counters, placed above and below the central tracking region, with two sets of four planes of Microstrip Gas Cham­bers (MSGCs) [2]. The dimensions of each chamber are 10 cm x 10 cm. Each set of the four planes of MSGCs provides two sets of orthogonal coordinates via two stereo planes in­clined at 5.7 °. Two additional fast timing counters, placed behind each other and just below the upper trigger counter give a good timing reference signal for the scintillator bar to be tested, which is placed between the two sets of MSGCs. The track impact point along the counter to be tested was reconstructed with a resolution better than 1 mm.

The cosmic muon timing, relative to the reference coun­ters, is independently measured by each of the PMTs at ei­ther end of the counter, after corrections are made for "time-walk" effects. The resultant resolutions are shown in Fig.2. The weighted average of the two measurements is of the or­der of ~ 60 ps, independent of the position along the counter. It was also checked that the timing resolution depends on

Resolut ion vs pos i t ion

10 Q. 140

120

100

-50 -40 -30 -20 -10 10 20 30 40 50

y ( c m )

Figure 2: Timing resolutions measured along the length of the counter.

the square-root of the total number of photoelectrons. A full Monte Carlo simulation, taking into account the measured values, shows that the required 40 ps timing resolution stated in the proposal, will be obtained with a suitable counter ge­ometry, the engineering studies of which are in progress.

REFERENCES

[1] M. L. Brooks era/., Phys. Rev. Lett. 83,1521 (1999).

[2] R. Bellazzini et al, Nucl. Instrum. Meth. A 457, 22 (2001).

29

AN ULTRACOLD NEUTRON FACILITY AT PSI

F. Atchison1, K. Bodek4, B. Van den Brandt1, M. Daum1, A. Fomin2, P. Geltenbort3, W. Gloor1, G. Heidenreich1, R. Henneck1, P. Hautle1, St. Joray1, S. Kalcheva2, A. Kharitonov2, K. Kirch1, S. Kistryn4, K. Kohlik1, J. A. Konter1, M. Lasakov2, S. Mango1,

A. Magiera4, V. Mityukhlaev2, H. Obermeier1, Ch. Perret1,1. Potapov2, U. Rohrer1, M. Sazhin2, A. Serebrov2, G. Shmelev2, V. Shustov2, J. Sromicki, R. Taldaev2, S. Teichmann1, H. J. Temnitzer1, D. Tytz2, V. Varlamov2, A. Vasiliev2, A. Zakharov2,

R-00-03, PSI 1 - PNPI 2 - ILL 3 - CRACOW4

not yet built up Figure 1:

Layout of the proton beam in front of the spallation UCN target. QBB7: quadrupole; PB3: vacuum pump; VBD3: vacuum valve; KBV2: shutter; MBH: beam profile monitors.

At PSI, we are building a new type of ultracold neu­tron source based on the spallation process[l]. The essen­tial elements are a pulsed proton beam with highest intensity (Ip ~ 2 m A ) and a very low duty cycle (~ 1 %), a heavy el­ement spallation target and a large moderator and converter consisting of about 301 of solid deuterium kept at a low tem­perature (~ 6 K) for the production of ultracold neutrons. For a few seconds, the proton beam is directed onto the spallation target and generates a high neutron density in a moderator assembly dedicated to the production of ultracold neutrons. The target is cooled and surrounded by a premoderator and neutron reflector consisting of ~ 4 m 3 of heavy water.

Monte Carlo calculations [2] show that a UCN density of more than 10 3 UCN/cm 3 can be delivered to the experiments using the proposed method. This is ~ 2 orders of magni­tude more than in experiments at the reactors in the Institute Laue Langevin, Grenoble and in the St. Petersburg Nuclear Physics Institute, Gatchina, which are the world leading cen­ters in ultracold neutron research.

In the year 2001, we have started to build up the proton channel feeding the UCN source. The setup of the beam line elements is displayed in Fig. 1. The main idea is to install the necessary shielding between the UCN source and the proton beam fines to the PIREX (Proton IRadiation Experiment) target station and the Proton Therapie complex. In this way, we can build up the UCN source installations independently from the beam operation in these facilities. All UCN specific additional beam line components of the proton channel, e.g. the fast kicker magnet, its power supply, the harp-like beam profile monitors, etc. are developped and ordered.

Further progress was made by the decision to extract the UCN into the NA hall at PSI (see Fig. 2, Area 2). This offers an experimental area of about 200 m 2 , fourfold the former size (Area 1). With these changes, we may add shielding in forward direction of the proton beam, and the duty cycle of

the UCN facility, formerly limited by shielding restrictions, may be increased from 0.5 % to ~ 1 % resulting in an UCN density increase of a factor of ~1.7.

REFERENCES [1] A. P. Serebrov et al., JETP Lett. 66, 803 (1997). [2] A. Fomin et al., PSI Report TM-14-01-01 2000, see

also http://ucn.web.psi.ch/proposals/ucn.techrev.pdf.

Figure 2: Layout of the Spallation Ultracold Neutron Source (SUNS) with experimental areas. EDM: Spectrometer for the mea­surement of the neutron electric dipole moment. To the right, one can see part of the future cyclotron installations in the NA hall.

30

MODERATOR SELECTION FOR THE PSI ULTRACOLD NEUTRON SOURCE

F. Atchison2, M. Daum2, St. Joray2, K. Kirch2, K Kohlik2,1. Potapov2, A. Serebrov2

R-00-03.1, PNPI 2 - PSI 1

The choice of the proper moderator material is of ut­most importance for the Spallation Ultracold Neutron Source (SUNS), because of its influence on the ultracold neutron (UCN) density inside the UCN intermediate storage trap[l]. We have made detailed calculations of the UCN density and of the thermal conditions which can be expected with var­ious promising moderator materials and for different mod­erator temperatures under the specific circumstances of our "macro-pulse" source design.

The calculational model is sketched in Fig.l; 590 MeV protons generate spallation neutrons in a lead target. The neutrons are thermalised in a moderator at ~ 3 0 0 K and pos­sibly in a cold moderator at 20-80 K. Ultracold neutrons are produced inside a solid deuterium (SD 2 , 5-8 K) converter of about 50 cm diameter. Some fraction of the UCN leaves the S D 2 and enters the storage trap. A shutter separates the pro­duction and trap volumes when there is no beam in order to avoid re-absorption of UCN on SD 2 .

U C N t rap ( t r u n c a t e d )

1 Shutter

UCNS

t $D.

MÊÊÊÊÊnÊÊÊÊÊÊ Cold moderator

t-1 tûtons

(argel

Moderator Figure 1:

SUNS calculation scheme.

The S D 2 composition and temperature as well as the neu­tron flux inside the SD 2 define the achievable UCN density. The SD 2 was assumed to contain admixtures of 0.2 % H 2

and 1 % para-D2. For all cases involving a D 2 0 reflector we have also used D 2 0 as the cooling medium for the proton target, and H 2 0 otherwise. In Fig. 2, the total heat loads in the S D 2 for different moderator materials is displayed on a logarithmic scale. The D 2 0 yields the lowest total heat load resulting in the lowest S D 2 temperature and a corresponding increase in UCN density; UCN loss factors for various con­figurations are presented in Table 1. The S D 2 position, with respect to the proton target, is the same for the first 8 cases. The distance is increased by 11 cm and 4 cm for cases 9 and 10, respectively, in order to reduce the heat load.

The following conclusions can be drawn from the results: (a) the largest S D 2 volume with the highest neutron flux can be accomodated with a D 2 0 reflector, (b) additional precool-ing of the thermal neutrons in a cold moderator does not in­crease the UCN flux obtained from S D 2 , (c) a D 2 0 reflec­tor yields 2.5-3 times more UCN than Graphite or Beryllium moderators (including additional losses due to H 2 0 cooling in the proton target for Be and C).

• 1 • • i i i i i i i

Pb target and . \ next moderators:

30 40 50 R(cm)

Figure 2: Total heat load in SD 2 vs. distance from the proton target.

Table 1: Relative UCN densities inside the trap; t p U j s e refers to the length of the proton pulse on target.

case moderator, S D 2 *pulse loss premoderator temperature,

thickness

*pulse factor

*) 1 D 2 0 , 300K 8K, 15 cm 4 s 1.0 2 D 2 0 , 300K 8 K, 5 cm 4 s 1.9 3 D 2 0 , 300K

LD 2 , 19 K 8K, 15 cm 4 s 1.0 4 D 2 0 , 300K

L D 2 , 19 K 8 K, 5 cm 4 s 1.2 5 C, 300K 8K, 15 cm 1.3s 4.6 6 C,300K

C, 80 K 8K, 15 cm 1.3s 5.0 7 C, 300K

C, 80 K 8K, 5cm 1.3s 7.9 8 C, 300K

C, 80 K 12K, 5cm 4 s 5.3 9 C, 300K 8K, 15 cm

+11 cm distance 4 s 2.0

10 Be, 300 K 8K, 15 cm +4 cm distance

4 s 2.1

*) Loss factor = (UCN density) , normalized to case 1.

REFERENCES [1] A. Fomin et al., PSI Report TM-14-01-01 (2000), and

F. Atchison et al., this Scientific Report (R-00-03).

31

MEASUREMENT OF THE ORTHO-D 2 CONCENTRATION IN THE SINQ COLD SOURCE

F.Atchison1, M. Daum1, R.Henneck1, T.Hofmann1, K. Kirch1,1.Potapov2, A. Serebrov2, H. Spitzer1, J. Wambach1, J. Wimmer1, A. Wokaun1'3, J. Zmeskal*

Paul Scherrer Institut1, St. Petersburg Nuclear Physics Institute2, ETH Zürich3, Osterreichische Akademie der Wissenschaften4

The planned PSI source for ultra-cold neutrons (UCN) will use solid deuterium as a converter for UCN production. Deuterium molecules can in principle be present in ortho-(nuclear spin 0,2) or para-modifications (nuclear spin 1). For the UCN source almost pure ortho-D2 is required because the energy up-scattering for UCN in collisions on para-D2 is about 2 orders of magnitude larger than on ortho-D 2.

Thermal equilibrium conditions yield c0 = 2 /3 at 300K, c0 = 0.95 at 25 K, and c0 > 0.999 at 4K. Whether thermal equilibrium conditions are obtained in cold neutron sources is not clear. The presence of high neutron and photon radi­ation fields can influence both, the conversion rates and the equilibrium composition.

For a liquid D 2 cold neutron source as in SINQ, a spe­cific c0 is much less important because the cross sections for collisions on different spin states are comparable at the relevant neutron energies. Values for c0 in liquid D 2 cold neutron sources have not been investigated in detail. The case is more important for liquid H 2 cold sources, however, there exist also only inconclusive data. Results, which were inferred from neutron flux measurements together with cal­culated expectation values, suggest an equal population of ortho and para states in liquid H 2 [1].

We have measured c0 for D 2 from the SINQ cold neutron source immediately after routine operation. About 1/3 of the D 2 is liquid at 25 K in the cold source and 2/3 are gaseous at room temperature in the tubes and storage tank. After warm­ing up the cold source one obtains a mixture of the tank gas with the formerly cold D 2 . Given c0 of the tank gas and of the mixture, c0 of the liquid D 2 during cold source operation can be deduced. Relaxation times for reconversion into room temperature equilibrium are long and can be measured.

D 2 gas samples were taken from the SINQ cold source gas system before and after shutdown in December 2001. Raman spectra of different samples were analyzed. c0 is obtained from a fit to relative line intensities of rotational transitions belonging to ortho states and para states, respec­tively. Knowing the relevant volume ratios and assuming complete mixture of the gas, from Figs. 2 and 3 one can deduce c0 = 0.86 ± 0.09 for the liquid D 2 in the SINQ cold source. Two prehminary conclusions can be drawn: (i) The result excludes the equal population of ortho and para states, (ii) The result is compatible with c0 = 0.95, i.e. thermal equilibrium in the liquid D 2 . This supports the assumption of thermal equilibrium conditions in the planned UCN source which, compared to SINQ, works at only 1% duty cycle.

REFERENCES

[1] K. Gobrecht, private communication (2001).

Fit States "ne£!o£(<t t îho)at taT: : c to r l r to , " 0.655+4.010 T * 3 2 7 K :

m a t u r e d I I I 91 peel 102 0.002175 0.002249 I13 0.001555 0.001577

135 0.000727 0.000724

146 0.000566 Q.QO0565

100 200 300 400

Figure 1: Rotational Stokes Raman Unes in D 2 taken from a gas cylinder as reference. A fit yields c0 = 0.66 ± 0.01, along with the sample temperature and one intensity scale factor. The horizontal axis is the wavenumber in c m - 1 .

0.4 x10'

0.35 -

0.3

0.25 p

0.2

0.15

0.1

FS St<*s5 !in<s« to rtwiho) atsd T;

c(ortho) - 0.713+-0.009 T - 3 3 9 K

measured fltfëxpect

I02 O001766 0.001803

[13 0000982 0.000973

[24 0002049 0.00199»

[39 0.000463 0.0004Ç7

[46 0000494 0.000495

j i i_ 100 200 300 400 500 600

Figure 2: Sample taken from the SINQ cold source gas tank before shutdown. c0 = 0.71 ± 0.01.

Fit Statosa \Xm& to cfortfto) ana T;

«(ortho) » 0.763+-O.031 T = 330 K

I02 0,000990 0.001079 113 0 .0005» 0.000446 I24 0.001043 0.001172 I35 0.O0Q176 0.000207

0.25

100 200

Figure 3: As Fig.2 but after shutdown. (The statistical accu­racy of this measurement is poor.) c0 = 0.76 ± 0.03.

32

MATHEMATICAL MODEL OF THE NEUTRON EDM EXPERIMENT

M. Daum2, A. Fomin1, R. Henneck2, K. Kirch2, A. Murashkin1,1. Potapov1, A. Serebrov2

R-00-05.1, PNPI 1 - PSI 2

One crucial problem for the EDM measurement by the Ramsey method with ultracold neutrons (UCN) is the sta­bility and homogeneity of the magnetic holding field, which ideally should remain constant over successive measurements with alternating electric field (for details on the new EDM experiment cf.[l]). In order to optimize the magnetic field (~ 2/xT) and the magnetic shielding over the large volume, static field and shielding calculations were carried out us­ing finite element and multiple iteration techniques. As a result, the optimum configuration of the four-layer /x-metal shielding was determined. The relevant axial shielding fac­tor (along the spectrometer axis) depends critically on the length differences of the cylinders DL and is ~2000. Also the residual field inside the shielding was calculated, includ­ing effects due to holes and due to slits between different el­ements of the shielding. The resulting inhomogeneity along the cylinder axis again depends critically on DL and has to be considered in the current distribution of the coils.

]-f=10"'T

-100 0 100 200 300 Distance, R[mm]

Figure 1: Field distribution (in fiT) in the EDM spectrometer.

The field distribution produced by an optimized coil con­figuration (over the full volume of the UCN chambers, R = 30 cm, L = 2 m) is presented in Fig. 1. The inhomogeneities, mainly produced by the gaps necessary for the UCN guides and for HV input, do not exceed 1 nT. Since the UCN av­erage over the volume of each chamber (R = 30 cm, L = 10 cm), the distribution shown comes very close to the re­quired homogeneity DB<0.03 nT between chambers. In any case, correction coils to compensate for residual small inho­mogeneities are foreseen.

0,24.

° 0,20. .O

2 0,16. o '

CO

•a 0,12

0,08.

0,04.

0,00.

2o=1,56-10 e-crrVnA

2n=2,12-10'~a-cm/hA (suppression by factor ~7¿

I I l ~ i —

-3,0x1o 2 7-2,0x1o 2 7-1,0x1o 2 7 0,0 1,0x1o27 2,0x1o 2 7 3,0x1o 2 7

d, ecm/nA

Figure 2: Distribution of the false EDM signal d;eafc (in units of e-cm/nA) due to leakage currents, analyzed for individual chambers (open bars) and for the full system (shaded bars).

As key element, the new spectrometer has a system of eight chambers with a high-voltage electric field (HV) and five chambers without HV. This will allow to investigate and to considerably reduce the influence of various systematic effects. A simulation of the experiment was performed with the purpose of (1) analysis of possible systematic effects, (2) calculation of the suppression of various systematic effects due to the multi-chamber system and (3) selection of the op­timum geometry of UCN chambers, UCN guides, polarizers, analyzers and detectors. The model allows simulating the effective resonance curves averaged over the volume of the chambers and considering spatial magnetic field variation up to 2nd order. The results show that the multi-chamber system indeed fully eliminates first order magnetic field variations, while second order variation effects are reduced by a factor ~ 5 .

The system response with respect to magnetic field varia­tions caused by leakage currents between chamber electrodes (~15 kV/cm) was evaluated with a Monte Carlo code simu­lating various current path possibilities on the basis of a leak­age current of ~ 1 nA (as observed in the ILL EDM experi­ment). In Fig. 2, the distribution of the false EDM signal dleak is shown, caused by leakage currents for two cases: (a) analyzing each chamber separately (open bars), and (b) using an analysis concept which exploits the multi-chamber system (shaded bars). The suppression factor with respect to leakage currents amounts to ~ 7 .

REFERENCES [1] A. Fomin et al., PSI Prop. R-00-05, and E. Alexandrov

et al., this Scientific Report (R-00-05).

33

THE MAGNETIC ENVIRONMENT FOR THE NEUTRON EDM EXPERIMENT

K. Bodek3, M. Daum1, R. Henneck1, K. Kirch1, M. Kuznick3, A. Serebrov2, A. Szelc3

R-00-05.2, PSI 1 - PNPI 2 - CRACOW3 - FRIBOURG - ST. PETERSBURG - ILL - HEIDELBERG

For the planned new measurement of the neutron EDM[ 1 ] at PSI, we expect to improve the sensitivity by about two or­ders of magnitude to 5 • 1 0 _ 2 8 e c m . The most crucial prob­lem is the stability of the magnetic holding field of ~ 2 liT. This is intuitively clear since the dipole moment is extracted from successive measurements, where the electric field di­rection is reversed, while the magnetic holding field is kept constant. Given the expected statistical uncertainty in the new experiment, the requirements for the stability and ho­mogeneity of the magnetic field are quite challenging: (a) temporal stability close to 1 0 ~ 1 4 T (rms) at frequencies of 1 to lOmHz, (b) spatial homogeneity along the solenoid field axis < 1 0 ~ 1 2 T/cm. As a consequence, it was decided to perform a test experiment in order to demonstrate that the necessary conditions for the magnetic field and for the reso­nance can be provided[2].

The design of an effective magnetic shielding requires detailed information on the ambient field and its variation. We have performed such measurements at various places in the experimental hall over a period of 2 months. We used a 3-axial fluxgate meter (Bartington Mag-03, internal noise ~10pT/\ /Hz (rms)) in a 1 Hz readout mode. Typical exam­ples of Bz(t) are shown in Figs. 1 and 2 (x corresponding roughly to the north-south direction) taken at the planned EDM position during night-time (Fig. 1) and working time (Fig. 2). The other two field components are qualitatively similar to Hx(t). While Fig. 1 displays the natural variation of the Earth field, the typical features in Fig. 2 are man-made, e.g. operation of the crane in the main hall (which was inter­rupted during lunch time), a small signal with a period of 500 s, and random spikes produced by cars and bicycles on the PSI internal road at about 10 m distance. The correspond­ing rms values taken from the raw data are 4 nT (Fig. 1) and

26 nT (Fig. 2). If one removes the slow variations by sub­tracting a sliding average one obtains 'residual' rms values of 0.5 nT and 2.6 nT, respectively. Thus, about InT rms appears to be the limit which can be obtained with a sta­bilized Helmholtz coil system surrounding the whole setup. We are developing a 3-axial Helmholtz system, where along 2 axes the ambient field is compensated in fixed mode while the field along the x-axis (= axis of the EDM spectrometer and shielding cylinders) will be actively controlled by flux-gates. Along x, the Helmholtz design is modified and in­cludes 4 coils (instead of 2), which reduces the field inhomo-geneities to below 10% over the full volume of the shield­ing and even better over the volume of the magnetic hold­ing field. We expect to remove the slow variations (t> 3 s) and to reduce the rms to ~ 1 nT in the frequency range 1 to 10 mHz. Fast singular 'spikes' created by bicycles and trucks are less than 100 nTs per integration time of 100 s, compa­rable to the expected stabilized rms and uncritical even when not completely eliminated by the stabilization system. With the ambient field stabilized to ~ 1 nT rms at frequencies of 1 to 10 mHz by the Helmholtz system, the required stability of 1 0 ~ 1 4 T can be achieved by a combination of additional mea­sures: (a) four-fold passive permalloy shielding (reduction factor 2 • 10 3 ) , (b) "shaking" (= continuous demagnetisation of the shielding, reduction factor 5) and (c) active stabiliza­tion of the Ramsey resonance condition (reduction factor 10) on the basis of 16 Cs magnetometers surrounding the HV chambers.

REFERENCES [1] A. Fomin et al., PSI Proposal R-00-05 (2000). [2] A. P. Serebrov et al., PSI Proposal R-00-05.2 (2001),

see also http://ucn.web.psi.ch/proposals.

THURSDAY 23.8.2001 (0:00 - 4:00) [LOCATION A]

1440 2880 4320 5760 8640 10080 11520 7200

TIME [5]

Figure 1 : The magnetic field component B^ (t)during night time (in liT).

Figure 2: The magnetic field component B^t) during working time (in liT).

34

THE MSCB BUS - A FIELD BUS TAILORED TO PARTICLE PHYSICS EXPERIMENTS

S. Ritt1, R. Schmidt1

R-99-05, PSI 1

Particle physics experiments require what is commonly referred to as "slow control". This includes the measurement and control of environment variables such as temperature, pressure and humidity as well as the control of high volt­ages for photomultipliers and wire chambers. While most experiment use an inhomogeneous mix of systems involving RS232, GPIB and PLCs, the MUEGAMMA experiment (R-99-05) will use a new slow control system developed at PSI, called MSCB (Midas Slow Control Bus). This system will be used for the 960 high voltage channels of the experiment, for the control of the liquid xenon xenon calorimeter and for the superconducting solenoid. The integration of all these systems into the central data acquisition and control system is essential for the long-term stability of the experiment. The MSCB system uses a field bus- like architecture, where a number of "nodes" are connected to a serial bus, which is controlled by a central PC. Each node contains ADCs, DACs and digital I/O for measurement and controlling tasks. For critical installations the control PC can be backed up by a secondary PC for redundancy. The PCs are connected to the Midas DAQ system [1], which allows for remote operation through a Web interface, history display, automatic alarm no­tification and for logging of slow control variables to tape. The hardware of a MSCB node is designed around a new generation of microcontrollers, which contain a 8051- com­patible microcontroller core, ADCs, DACs and digital I/O on a single chip. We currently use the ADuC812 [2] from Ana­log Devices and the C8051F000 from Cygnal [3]. The nodes are connected via an RS-485 bus running at 384 kBaud. A segment can contain 256 nodes, and with one layer of re­peaters 65536 nodes can be connected and addressed on a single bus. Two versions of MSCB nodes have been devel­oped. A stand-alone module (Fig. 1) which can be embedded directly on a sensor or on an electronics board is powered from the bus, which uses a 10-wire twisted pair flat ribbon cable for distances up to 500 m. The production cost of such a node is about 50 CHE A development kit for the Cygnal controller which includes a C compiler costs 99 US$.

In addition to the stand-alone module, a 19" rack system which hosts cards containing a MSCB node and signal con­ditioning, has been designed. Cards were made for voltage, current and temperature measurements as well as to control 220V consumers such as heaters. The MSCB bus runs on the back plane of the crate.

Using the local intelligence of the node controller, reg­ulation loops (PID) and interlock systems can be realized without intervention of the central control PC. The nodes run a simple framework for the communication with the host system, which guarantees real-time behaviour. User routines can be added to implement application- specific logic. The nodes can be reprogrammed over the RS-485 bus.

The MSCB protocol was optimised for minimal over­head. A 16-bit value from a node can be read out by sending

Figure 1 : Stand-alone node with an RS-485 transceiver, eight channel 12-bit ADC, two channel 12-bit DAC, 16-bit digital I/O and a temperature sensor. The right connector is for the MSCB bus, the one at the back for an optional LCD display.

a request of three bytes and receiving a reply of four bytes, both including a code (CRC) to avoid data corruption. De­pending on the number of nodes, a MSCB system can either use 8-bit or 16-bit addressing. A node can contain up to 256 "channels" for reading and writing and up to 256 "configu­ration parameters", which are stored in the EEPROM of the node and can for example be used as constants for PID reg­ulation. Each channel and parameter is described by a set of attributes such as name, physical units and status. These attributes are stored in each node and can be queried from the control PC, making the configuration of large networks very simple. A special repeat mode has been defined which allows the readout of a series of nodes in less than 300 ps per node.

For the control PC a "C" library has been developed run­ning under Windows and Linux. Based on this library, a Lab-View driver and a driver for the Midas DAQ system are avail­able. Simple Lab View applications such as a data logger with graphical display have been implemented.

A prototype of the MSCB rack system is currently used for the pressure and high voltage control of the new propor­tional chamber for the SINQ POLDI detector.

The final system will be available from the PSI electron­ics pool in spring 2002 upon request. It can be concluded that the MSCB system is an attractive alternative to GPIB multimeters and to Programmable Logic Controllers with re­spect to cost and integration. For more information visit the MSCB home page at http://midas.psi.ch/mscb.

REFERENCES

[1] MIDAS home page http://midas.psi.ch

[2] http://products.analog.com/products/info.asp?product= AduC812

[3] http://www.cygnal.com/products/C805 lF000.htm

35

FULLY CONFIGURABLE DATA ACQUISITION SYSTEM FOR SINQ INSTRUMENTS

N. Schlumpf, U. Greater1, Ch. Buehler1, P. Rasmussen1, M. Koennecke2, D. Maden3,

PSI/TEM1 - PSI/FUN 2 - PSI/SLS 3

We report on the realization of our fully configurable data acquisition hardware for the SINQ instruments. This sys­tem allows for the collection of the different data entities and event related signals generated by the various detector units. It offers a variety of synchronization options including a time measuring mode for time-of-flight determinations down to resolutions of 100 nsec. Based on configurable logic (FPGA, CPLD) event-rates up to the MHz range can be processed and transmitted to a programmable on-line data reduction system (Histogram Memory).

n-beam t;on<1itfarilntJ System

SIMLL|>l« 4 L : Analyzer Detection-n-beam t;on<1itfarilntJ System

System : System S y stem

590 M e V 8

• Monochro­mators

• Choppers

* Fitters • Analyzer Detectors

• one/two dimensional Detectors

Sample Magnets

Power-

Motors

abs./mcr R**<idvwr».

Analog & Digital l/O's

Additional Steering and Control Units

Magnet Control Units

Motor Control Units

Program­mable

Controller

.Monitors,.

amplifiers :

Tsiminai - Server

33

Figure 1: General layout of the diffraction instruments.

The data acquisition- and instrument control-system is shown in Fig. 1. The concept exploits the philosophy of a modular structure with distributed intelligence. The DAQ task is subdivided into experiment control (DAQ Com­puter), acquisition control (Neutron Counter), position en­coding (e.g. ADC, TDC), data-grabbing (Multi-Detector In­terface, MDI), and data processing (Histogram Memory). The Ethernet connected DAQ Computer controls the various RS232 based subsystems such as motor- and temperature-controllers, Neutron Counter, MDI and programmable logic controller. The Histogram Memory is implemented on a VME Power PC module running a real time operating sys­tem (VxWorks) and is connected to the Ethernet, allowing fast transmission of the histogrammed data to the quick-look facility and to the final data storage medium located on an Instrument Server. A more detailed description can be found in [1].

Up to now the following detection systems have been imple­mented: • delay-line based 2D detectors from EMBL

at AMOR and TriCS [2], • 2D array of 383 single 3 He counter tubes at FOCUS, • 1-D and 2-D 3 He multi-wire proportional chambers

from CERCA at HRPT and SANS [3], • 1-D B F 3 multi-wire proportional chamber

from LMT at DMC.

Each detector type requires a dedicated readout system. Our concept has been developed with the aim to standardize the SINQ DAQ-System and to reduce the specific hardware to position encoding units. Most recently we developed a series of position encoder modules for the delay-line based 2-D de­tectors using sub-nanosecond multi-channel time-to-digital converters (mC-TDC). The mC-TDCs use the propagation delay of individual CMOS gates as fundamental time quanta. The achieved time resolution of 145 psec allows to mea­sure the time-encoded position with an ultimate resolution of ~ 50 /Ltmx50 /LTM. Due to the pipelined TDC architecture event rates exceeding 100 keps can be processed. The mC-TDC electronics further generates low-jitter time-of-flight signals and incorporates an efficient two-stage pileup rejec­tion mechanism. The mC-TDC is described in detail else­where [2]. Fig. 2 shows the measured impulse response of both, the mC-TDC electronics and the entire TriCS instru­ment. The analysis of the impulse profiles of the mC-TDC electronics and the TriCS instrument yield FWHM-values of 0.16 mm and 1.96 mm, respectively. Clearly, the spatial res­olution of the TriCS (and AMOR) instrument is dominated by the spatial resolution of the area detector.

200 -,

CO

c 150 -O

O c 100 -0 l _

"3 50 50

z 0

800 800

AX [TDC - Units]

Figure 2: Impulse response of the TriCS instrument (broader peak from a neutron beam clipped to 300 pmx 300 pm) and the mC-TDC electronics (narrow peak from ñxed pulse delays) . The displayed region is ~ 36x 36 mm2 and covers 5% of the active detector area.

REFERENCES

[1] U. Greutereí ai, ICNS 2001 Proceedings, Appl. Phys. A, in press.

[2] Ch. Buehler et ai, ICNS 2001 Proceedings, Appl. Phys. A, in press.

[3] P. Rasmussen et ai, ICNS 2001 Proceedings, Appl. Phys. A, in press.

36

37

L a b o r a t o r y fo r A s t r o p h y s i c s

38

LABORATORY FOR ASTROPHYSICS

Alex Zehnder and Manuel Güdel

Research in astrophysics strongly focused on the rich harvest from the first two years of observing with the XMM-Newton satellite. After its successful launch at the end of 1999 and an extended calibration and test observation phase during the year 2000, the rather complex multi-telescope satellite proved its full functionality, so that a first suite of 56 science papers could be published by the international XMM-Newton team in a special issue of the Astronomy and Astrophysics journal, comprising a total of 352 pages. Our small astrophysics team at PSI leads or participated in 9 of these articles related mostly to stellar atmospheres and stellar winds, but also to X-ray emission from supernova remnants.

PSFs earlier involvement in the development of XMM-Newton's Reflection Grating Spectrometers now allowed the PSI astrophysics team to participate in the extensive guaranteed time program, part of which was organized previously by our astronomers. Most of the cool and hot-star targets were scheduled and observed during 2000, inducing extensive data analysis efforts and scientific interpretations that will continue during the next years.

Among the internationally recognized highlights of the new findings were results on the composition of stellar atmospheres. Contrary to expectation, the elemental composition of magnetized stellar coronae is not identical to the bulk composition of the star itself, but depends systematically on the level of magnetic activity in the stars. While abundance anomalies have been suggested for several years, XMM-Newton data showed for the first time a systematic trend related to the ionization potential of the elements in active stars. It has further become possible to spectroscopically study densities in stellar plasmas, in particular time variations of the thermal pressure in magnetized plasmas. Further studies related to massive binaries in which colliding winds produce very hot shock-heated plasma, to eclipsing binaries for which the X-ray light curves give hints on the atmospheric structure, and to young and forming stellar clusters for which the large field of view of XMM-Newton proved essential.

Our results were widely distributed through our participation in several X-ray conferences. A large number of proceedings articles, including several invited reviews, give an overview of the results obtained and interpreted so far.

A complementary effort concentrated on high-resolution long-baseline radio interferometry data of young, contracting stars. We have for the first time spatially resolved and imaged a young star that is thought to be at a transition between a "protostar" and a "classical T Tau" star. The data seem to suggest the presence of very strong

(kGauss) magnetic fields in this system, possibly related to the presence of an accretion disc.

There were also strong developments in the field of solar plasmas, mostly in preparation for the upcoming Hessi mission. Theoretical issues concentrated on particle acceleration in irregular magnetic field topologies and on the simulation of the so-called Firehose Instability. These efforts should lead to a better understanding of the sources and mechanisms of energy release in the solar atmosphere, a field of main focus for Hessi.

Meanwhile, the Hessi European Data Center (HEDC) has been completed and inaugurated at ETH Zurich; it will be of prime importance for the users once data are coming in. One of the reports describes the main functionalities of the HEDC.

After the delivery of HESSI Imager in Sept 2000 for integration into the spacecraft, we were forced to wait almost 1 Vi year. Several problems, not related to the HESSI Pegasus rocket, delayed the launch that finally took place February 5, 2002. However the time was used to finish and test the aspect reconstruction software, a deliverable item of PSI.

The cryogenic photon detector development became our main hardware activity. Two post-doctoral physicists joined our team and our long-term goals were defined. We are working on a pixel detector that has single photon counting capability in the optical wavelength regime with position and energy resolution.

The fabrication of Ta strip detectors with two superconducting tunneling junctions as read-out devices is now well under control. Devices could be sold to a commercial company, GenSpec, where they are used successfully in a time-of-flight apparatus to determine the mass of bio-molecules.

Ou work on microcalorimeters using superconducting transition edge thermometer devices gave promising results. Our first Mo/Au device operating at 100 mK gave an energy resolution of 20 eV when illuminated with 6keV photons.

In order to support our research activity, we decided to purchase a dry adiabatic demagnetization refrigerator with a base temperature of 50 mK and a He3 refrigerator. These instruments will be delivered in 2002. We plan to prepare one instrument for observations on an optical telescope.

39

ELEMENTAL ABUNDANCES IN STELLAR CORONAE WITH XMM-NEWTON

M. Audard1, M. Güdel1, and the RGS Consortium2'3'4

PSI 1 - SRON/NL 2 - COLUMBIA UNIV/USA 3 - MSSL/UK 4

The Reflection Grating Spectrometers on board XMM-Newton produce excellent high-resolution X-ray spec­tra to study physical processes occurring in stellar coronae. Coronal abundances in active stars have been found to dis­play a depletion of metal abundances relative to solar photo-spheric abundances. New results from the XMM-Newton RGS show a relation between the abundance of a trace element and its first ionization potential (FIP): the elemen­tal abundances increase with increasing FIP [1]. Although coronal abundances in the Sun show a FIP bias as well, low-FIP elements (FIP < 10 eV) are overabundant by a factor 4 — 6 relative to the high-FIP elements. Such a bias points toward a fractionation mechanism in the solar chromosphere, where the temperature is sufficient to ionize low-FIP ele­ments but leaves high-FIP elements at a neutral stage. The "inverse First Ionization Potential" effect has been found in the most active stars [2]. This FIP bias could be interpreted as an overabundance of high-FIP elements, or as an under-abundance of low-FIP elements. It may however also simply reflect the stellar photospheric composition which is largely unknown or very uncertain in active stars. We have circum­vented this problem and extended our analysis to inactive stars by studying solar analogs of known photospheric com­position (Fig. 1, top). We found a transition from an inverse to a normal First Ionization Potential effect with decreasing activity, or increasing age [2, 3]. Low-FIP elemental abun­dances significantly vary with activity, while the high-FIP composition stays constant (Fig. 1, bottom). There are how­ever suggestions that this scheme may be simplistic: the old, inactive Procyon displays no FIP bias. A successful model of the fractionation mechanism will have to explain the relation between selective enrichment and overall coronal activity.

We have put forward first ideas to explain the inverse FIP effect seen in active stars: downward propagating electrons detected by their gyrosynchrotron emission in active stars could prevent chromospheric ions (mostly low-FIP elements) from escaping into the corona by building up a downward-pointing electric field [3]. As the density of high-energy electrons decreases with decreasing activity, the inverse FIP effect is quenched. During large flares, however, the high-energy electrons heat a significant portion of the chromo­sphere to bring up a near-photospheric mixture of elements into the corona, and this effect has indeed been observed. The new results by XMM-Newton have thus opened a new field of research relevant to the physics of heating and dy­namics of outer stellar atmospheres.

REFERENCES

[1] A. C Brinkman, E. Behar, M. Güdel, et al., Astron. Astrophys. 365, L324 (2001).

13.0 13.5 14.0 14.5 15.0 15.5 wavelength (A)

10.0 ;—i 1 1 • 1 1 1 • 1 1 1 • 1 1 1 1 • 1 • r-

•* :

• • •

L o w - F I P

:

_ i 1 i i i 1 i i i 1 i i i 1 i i i 1 i i

•

i 1 i i

•

1 1 1 .

H i g h - F I P :

2 4 6 8 10 Average Temperature (MK)

12 14

Figure 1: Top: Extracts from XMM-Newton RGS spectra of solar analogs ordered in decreasing activity (or increas­ing age) from top to bottom. The labeled lines are formed at the same temperature, thus different coronal composition is believed to produce the decreasing line ratio (Ne/Fe) with decreasing activity. Bottom: Coronal abundances (normal­ized to O) versus the coronal temperatures, for Fe (low-FIP; top) and Ne (high-FIP; bottom). The data include sources of various activity levels, from inactive to very active stars.

[2] M. Audard & M. Güdel, in New Visions of the X-ray Uni­verse in the XMM-Newton and Chandra Era, in press (2001).

[3] M. Güdel, M. Audard, A. Sres, R. Wehrli, R. Mewe, Astrophys. J., submitted (2001).

40

SPECTROSCOPIC CORONAL DENSITY MEASUREMENTS WITH XMM-NEWTON

M. Güdel1, M. Audard1, M. Horvath1'2, K. W Smith1'2, S. L. Skinner3, J. L. Linsky3, J. J. Drake4

PSI 1 - ETH ZÜRICH 2 - COL UNIV/USA - SAO-Sf A/USA

XMM-Newton's high spectral resolution has been used to measure for the first time the density evolution during a flare on a nearby star by using He-like density-sensitive line triplets of oxygen and neon. Very high electron densities (several times 1 0 n c w - 3 ) are seen to build up and to decay rapidly.

Stellar coronae are thought to ultimately derive their ther­mal energy from magnetic fields anchored in the photosphere. The mechanisms that heat the plasma to 10 6 — 10 7 K are not well understood, however. During flaring episodes, mag­netic reconnection is believed to explosively release energy stored in non-potential magnetic fields. In a standard sce­nario, a large fraction of the energy is channeled into en­ergetic electrons (> 10 keV) that travel along the magnetic fields to lower atmospheric layers where they collide and heat the plasma to coronal temperatures. The resulting overpres­sure drives the material into the coronal loops where it cools by radiation and conduction. A detailed modeling requires precise knowledge of the electron density in the flaring re­gion. Conventional measurements provide a measurement of the emission measure, i.e., the product of the square of the electron density and the volume rather than the individual parameters.

High-resolution X-ray spectroscopy provides access to He-like triplets that are density-sensitive. The triplets con­sidered here consist of a resonance transition (r, I s 2 1 5 o — ls2p1Pi),anintercombinationtransition^, I s 2 1 5 o — l s 2 p 3 P i j 2 ) , and a forbidden transition (/, I s 2 1 5 o — l s2s 3 S i ) at very similar energies. In a coronal plasma, excitation is by col­lisions, while decays are radiative. In a coronal low-density environment, the flux ratio f/i > 1, while a significant in­crease in density can excite electrons from the upper level of the forbidden transition to the upper level of the intercom­bination transition, thus leading to smaller f/i flux ratios. The flux ratio can be used to infer the electron density (e.g.,

D e n s i t y - S e n s i t i v e T r i p l e t s

Figure 1: Examples of the O VII (left) and Ne IX (right) triplets at various phases of the flare (see Fig. 2). Low-density examples (f/i high) are shown in the upper planels, low-density examples in the lower panels.

Figure 2: Time history of the X-ray flux (solid line) and cor­responding density values measured in OVII (error bars, in­dicating 1er errors in flux and the time interval considered along the time axis).

Porquet et al. 2001). The XMM-Newton Reflection Grating Spectrometer cleanly separates the O VII triplet around 22 Â representing plasma of 1 — 3 x 10 6 K. It also separates the triplet of Ne IX (~ 3 - 6 x 10 6 K) although blends with lines from highly ionized iron make line measurements problem­atic.

We obtained high-quality observations of the nearest star apart from the Sun, the M dwarf Próxima Centauri, with XMM-Newton. The observation recorded an extremely strong X-ray flare, increasing the X-ray flux by a factor of ~ 8 0 above the quiescent level and allowing us, for the first time, to measure the evolution of the coronal density.

A rapid increase of the electron density by at least an or­der of magnitude is found for the flare peak times. Densities reach several times 1 0 1 1 c m - 3 and decay rapidly to low lev­els during the flare decay, as seen by a rapid change in the f/i flux ratios (Figure 1). Pre-flare densities are found to be at least an order of magnitude smaller. The density correlates well with the overall X-ray flux (Figure 2), which should be expected since the emissivity of a plasma scales with n2.

REFERENCES

[1] D. Porquet, R. Mewe, J. Dubau, A. J. J. Raassen, J. S. Kaastra, Astron. Astrophys. 376,1113 (2001).

41

VLBI OBSERVATIONS OF T TAURI SOUTH

K.W. Smith1'2, M.Güdel1, M. Pestalozzi3, J. Conway3, A.O. Benz2

PSI 1 - ETH ZÜRICH 2 - ONSALA OBS 3

T Tauri stars are young stars in the process of collapse to­wards the main sequence. Accretion of material onto the star proceeds via a disc. Magnetic processes in the inner regions of the system lead to the formation of collimated jets and wider bipolar outflows. These tend to be more pronounced in younger objects (embedded protostars), but in many cases persist into the Classical T Tauri phase.

The T Tauri system consists of two components lying roughly on a north-south axis and separated by about 0.7". T Tauri North dominates the optical emission. T Tauri south is significantly redder and more embedded. The Southern component dominates the system in the radio, with a flux of 4-5mJy at 3.6cm. Circular polarisation and short timescale variability suggest a non-thermal synchrotron emission mech­anism. The rotation period of the optical component of 2.8 days coupled with a vsini measurement of around 20km/s and a stellar radius estimated (from tracks) to be 4.5R Q im­plies an inclination to the observer's Une of sight of only around 15°. It has been suggested that the peculiarities of the system may be explained by this pole-on view. 6cm MERLIN observations revealed that the T Tauri South emis­sion was divided into two circularly polarised blobs of op­posite helicity (Ray et al, 1997). It was suggested that these might be outflowing material associated with a recent out­burst. The polarisation properties suggest a strong ordered magnetic field associated with the outflow on AU scales.

We observed T Tauri South with the VLBA, incorporat­ing also the phased VLA and the 100m Effelsberg telescope in Bonn. The intention was to probe the inner regions of the system in order to study the collimating mechanism of the jet at higher resolution than previously achieved. We reduced the VLA data separately in order to get a first look at the situ­ation. This revealed that T Tauri South underwent two strong outbursts, brightening by about 50% on a timescale of min­utes. This activity was accompanied by dramatic changes in the helicity of the circular polarisation. The second event ap­pears to be 100% right-hand polarised, something which to our knowledge has never been seen previously in an accret­ing pre-main sequence system (see Figure 1). This indicates a coherent emission mechanism and suggests strong (2-3kG) associated magnetic fields.

Figure 2 shows the real part of the T Tauri south visi­bilities plotted against UV distance for all the VLBI base­lines. There is clear evidence that T Tauri south is resolved. When the data are divided up in time according to the vari­ous phases of activity, the minimum is seen most clearly after the first flare, although the preñare data shows some signs of resolution. The last segment suffers from a lack of signal and an absence of baselines over about 50MA.

We mapped T Tau South before and after the first flare event. Figure 3 shows contour plots of T Tauri South be­fore and after the first brightening. It is clear that the source is much stronger in the second plot. Furthermore, there is

evidence of extension to the northeast. The length scale of this would be between a quarter and half an AU. Such length scales seem long for magnetic structure associated with the star, but may indicate magnetic structures associated with the inner disk. Alternatively, we may be seeing a close binary system.

Figure 1 : Lightcurves for RR and LL polarisations.

UV dlaunc« (H>)

Figure 2: Real part of the visibilities against baseline sepa­ration, (a) all data, (b) before the first flare, (c) between first and second flares, (d) after second flare.

Figure 3: Contour plots of the source in the first half of the experiment (left) and in the second half.

REFERENCES

[1] Ray et al., Nature 385,415 (1997).

42

PARTICLE ACCELERATION IN IRREGULAR MAGNETIC TOPOLOGIES

K. Arzner

High-energy particles are ubiquitous in astrophysical plas­mas such as the Earth magnetosphere or the solar corona. The energies of these particles are many orders of magni­tude above the ambient equilibrium level, and they manifest themselves in the form of non-thermal radiation. The HESSI spacecraft, planned for launch in 2002, will observe hard X rays and gamma ray lines emitted in solar flares with high spectral and spatial resolution, which is needed in the light of preceding flare observations which reveal that accelera­tion of energetic particles takes place within fractions of a second ( ^ 10 keV) or a few seconds ( ^ 1 MeV).

In order to explain this dramatic gain in kinetic energy several models have been proposed, including shocks, mag­netic reconnection, and stochastic acceleration. Most of these models rely on simplified geometries which admit exact or adiabatic motion integrals and the application of perturbative methods. In contrast, the author of the present report investi­gated the motion in a stochastic two-dimensional magnetic field with oß(x,z) > (B) by means of percolation the­ory. Such fields model strong magnetic turbulence, and the motion can be described in terms of an equivalent potential <£> = (Py — qAy)21'2m (see Fig. 1). Clearly, the motion is

0 2 4 e e i o o s 4 e a 10

x/l x/l Figure 1: The investigated two-dimensional stochastic ge­ometry: In-plane magnetic field lines (top) and equivalent potential (bottom), with example trajectory.

restricted to <£> < E with E the particle energy, a statement which represents an alternative to the 'fieldline tying' the­orem of Jones and Jokipii [5]. Applying percolation theory [4] and assuming that Ay is a sign-symmetric random field, it can be shown [1] that there exists a critical energy E®, below which a particle is bounded with probability one:

The boundedness of motion is relevant for mobility questions (i.e., 'cross-field' diffusion), and for the onset of efficient ac­celeration in the presence of an electric field £. Following the latter line of reasoning, the above model was generalized to include an electric field (0,0, £ ) . This amounts to a tilted potential (Fig. 2, left) from which particle runaway occurs if the nearest saddle points have sufficiently declined. In or­der to determine the escape (acceleration-) probability, we consider the connectivity tz(L), i.e., the probability that a randomly chosen point (x, 0) is connected to the line z = L.

Figure 2: Particle escape in the presence of an electric field. Left: energetically forbidden (black) and accessible (white) domains for a Gaussian random field Ay with vari­ance a\ and Gaussian two-point function with correlation length Z=2.8 cells. Right: connectivity tz(L) for different values of the dimensionless electric field e = 2ml/{qa2

A) £. Solid line: Monte Carlo simulation. Dashed: analytical model based on scaling theory. Further parameters used are: Py/(qaA) = 1.5 and 2mE/(q2a2

A) = 1.

For £ = 0, this quantity is believed to decay exponentially, tz(L) ~ e - L / í with £ oc \E - £ ° | - 4 / 3 - a behaviour which is confirmed by extended Monte Carlo simulations (Fig. 2 right, e = 0). For £ > 0, tz (L) can be estimated analytically [2] (Fig. 2 right, dashed) and tz(OO) represents the geomet­rical escape probability. It is found that, averaged over an ensemble of magnetic fields, runaway of initially resting par­ticles occurs if £ > £ c , where £c = kql(B2)/m and the constant depends on the required escape probability.

In the collisionless model, £ c plays a similar role as the Dreicer field [3] in a collisional plasma. Scattering on mag­netic inhomogeneities replaces the Coulomb collisions. Con­trary to the classical Dreicer scenario which favours electron acceleration, the 'collisionless Dreicer field' £ c is lower for ions because these become demagnetized before the elec­trons. The proposed model is attempted to be help under­standing ion acceleration in the (collisionless) solar corona.

REFERENCES

[1] K. Arzner, M. Scholer, R. Treumann, Percolation of charged particle orbits in two-dimensional irregular magnetic fields, to appear in J. Geophys. Res, 2002.

[2] K. Arzner, A percolation model of a "collisionless Dreicer field", in preparation.

[3] Dreicer, H., Electron and ion runaway in a fully ionized gasI/II, Phys. Rev. 117, 329/343 (1960).

[4] M. B. Isichenko, Percolation, statistical topography, and transport in random media Rev. Mod. Phys. 64,961 (1992).

[5] F. C. Jones, J. R. Jokipii, M. G. Baring, Charged-particle motion in electromagnetic fields having at least one ig­norable coordinate, Astrophys. J. 509,238 (1998).

43

TEST-PARTICLE SIMULATION OF THE ELECTRON FIREHOSE SIMULATION

G.Paesold1'2, A.O.Benz1

ETH ZURICH1 - PSI 2

An electron distribution with a temperature anisotropy T\\/T±_ > 1 can lead to the Electron Firehose instability (EFI) (Here parallel and perpendicular denote directions relative to the background magnetic field B0). Since possible particle acceleration mechanisms in solar flares exhibit a preference of energizing particles in parallel direction, such an anisotropy is expected during the impulsive phase of a flare. The EFI is investigated in linearized theory and test-particle simulations. Due to its non-resonant nature, standard theories for resonant wave-particle interaction cannot be applied to this instability. The work is focused on the analysis of time scales and efficiency of the electron isotropization as the plasma reacts to the instability.

It is known from analyses in linearized kinetic theory (Hollweg & Volk [l];Pilipp & Volk [4]) that an anisotropic plasma (T\\/T± > 1) can become unstable to the so-called Electron Firehose instability (EFI). The EFI is a extension of the well known (MHD) Firehose instability, originally men­tioned by Parker [3]. While the Firehose instability is of en­tirely non-resonant nature the EFI involves resonant protons with the electrons remaining non-resonant. It has been estab­lished in a former work (Paesold & Benz [2]) that Electron Firehose (EF) waves can well be excited in the course of the acceleration processes during solar flares. Some of the acceleration processes possibly being responsi­ble for bulk energization during solar flares require a pitch angle scattering mechanism in order to maintain efficiency of acceleration (e.g. transit-time damping). The EFI could deliver such a process as an intrinsic feature of the accelera­tor itself.

Due to its non-resonance, standard theories are not applicable to the problem of electron scattering in a field of EF waves. Test-particle simulations were carried out in order to answer the question whether the EFI is a viable pitch angle scattering mechanism. Figure 1 shows the result of a typical simulation

1 0 0 . 0 0

1 0 . 0 0

*cr> <u jo 1.00

0 . 1 0

0 .01

Variance of Gyrocenter Distribution :

to :

2 0 4 0 6 0 T ime [fi p-']

Figure 1: Time series of the variance of 500 electrons in the field of 530 EF waves.

run. The electron scattering in pitch angle is analyzed in ob­serving the temporal evolution of the variance of an ensem­ble of electrons (500 particles herein), initially distributed in a delta peak in velocity space.

There are two different regimes: a linear increase in vari­ance in the beginning of the scattering process and a region of saturation, where the particles are not further scattered. Two values therefore characterize the scattering process: a saturation time io and a saturation value of the variance a 2

a t . Figure 2 shows the saturation values in variance for fixed v±

S t e a d y S t a t e Value of a2

1 0 0 0 1 0 0 0 0 In i t ia l pa ra l l e l k i ne t i c e n e r g y in k e V / n u c l e o n

Figure 2: Saturation values of a2 for fixed v± vs. initial parallel energy. The vertical dashed lines indicate the thermal perpendicular and parallel energies.

vs. initial electron energy. The values are independent of the initial parallel energy of the electrons which is an indicator of the non-resonance of the electrons. The results of the analysis yield as typical time scales for the scattering process t & 10/flp and for the typical mean square spread in pitch angle of an initial delta peak in velocity space of about ~ 4 deg. These values suggest that the EFI can well deliver a viable pitch angle scattering mechanism for bulk energization mechanisms in solar flares.

REFERENCES

[1] J. V. Hollweg, H. J. Volk,

J. Geophys. Res. 75/28, 5297 (1970),

[2] G. Paesold, A. O. Benz, A&A, 351,741 (1999).

[3] E. N. Parker, 1958, Phys. Rev. 109,1874 (1958).

[4] W. Pilipp, H. J. Volk, J. Plasma Phys. 6, 1 (1971).

44

RADIAL DIFFUSION - CAUSE OF THE RELATIVISTIC ELECTRON ENHANCEMENTS IN THE OUTER RADIATION BELT?

P. Bühler

The Earth's outer radiation belt is highly dynamic. Dur­ing geomagnetic active periods the trapped > 1 MeV elec­tron fluxes can change by several orders of magnitudes within a day or so [1]. Whereas it was known for long time al­ready, that during geomagnetic quiet periods the dynamics of the radiation belts is dominated by so-called radial diffusion and losses due to wave-particle interactions, the mechanisms leading to the fast enhancements is still a subject of debate.

There are two main classes of proposed mechanisms. One states that the source of these electrons is beyond geostation­ary orbit (GEO) and that the enhancements observed within GEO are due to rapid inward diffusion of the source pop­ulation. The other states that there is a local source or ac­celeration mechanism within GEO. Both classes of theories are compatible with the observational fact, that the enhance­ments are promoted by strong, long-lasting geomagnetic ac­tivity [2] - both, radial diffusion and waves, which are po­tential causes for a local heating, are enhanced during such periods.

In case of a local source in the inner magnetosphere one would expect to observe a local peak in the radial distribu­tion of the phase space density (PSD) at fixed first (M) and second (K) adiabatic invariant. Figure 1 shows radial distri­butions of PSD ( M = 2100 MeV/G, K = 0 G1'2 • km) as observed at different times during an enhancement phase with the particle detector REM from PSI [3], which was or­biting the Earth for four years in an equatorial geostationary transfer orbit (GTO).

3 4 5 6 7 L [RJ

Figure 1: L-profiles of the phase space density of trapped electrons in the Earth's outer radiation belt during the re­covery phase of a geomagnetic storm. The density increases within a few hours over a large L-range.

There is obviously no clear local maximum observed, which rules out the dominance of a local source scenario. However, within the temporal resolution given by the orbit period of approximately 10 h, the enhancement seems to take place almost simultaneously over a large radial range. Since the typical time scale for quiet time radial diffusion is of the order of several days, the question arises whether radial dif­fusion alone can account for the observations.

Radial diffusion happens due to the violation of the third

adiabatic invariant under conservation of the first two. Mag­netic and electric field changes with time scales shorter than the drift frequency of the trapped particles are the cause of such violations. And since field variations are most intense during geomagnetic active periods, radial diffusion is expected to be enhanced then.

In order to address this question we numerically solved a lossy-diffusion equation for PSD as function of time and radial parameter L. As boundary condition we imposed the measured values at L = 6.5. Diffusion coefficient and loss time are functions of energy, L, and geomagnetic activity pa­rameter Kp and are based on theoretical estimations and ob­servations.

In Figure 2 observations and model results are compared. The rapid enhancement at L > 4.5 RE is fairly well repro­duced by the model. At lower L-values, where the relative enhancement is much lower, the inward diffusion of electrons must be compensated by losses due to pitch angle scattering. There the results are most sensitive on the chosen model pa­rameters and further investigations are needed.

January February 1995

Figure 2: Observed (squares) and simulated (diamonds) phase space density at different L-values. Using a lossy-diffusion model the rapid enhancement of the density can be reproduced fairly well.

Observations and simulations suggest that at the equa­tor inside GEO, radial diffusion can lead to rapid relativistic electron enhancements as is observed. With this however, the question remains what the origin of the source population be­yond GEO is and how it is produced.

REFERENCES

[1] P. Bühler et al., Observations of the Earth's outer radia­tion belt during magnetic storms, PSI Annual Report Annex m/A, 145 (1997).

[2] P. Bühler et al., Who cares about weak geomagnetic storms, PSI Annual Report Annex 1,46 (1998).

[3] P. Bühler et al., Radiation Environment Monitor, Nucl. lustrum. Meth. A 368, 825 (1996).

45

BROWSING AND PROCESSING HESSI DATA AT THE HESSI EUROPEAN DATA CENTER

Pascal Saint-Hilaire1'4, Etzard Stolte2, Christoph von Praun3, Arnold O. Benz1

ETHZ: Institutes of Astronomy1 and Information Systems 2, Laboratory for Software Technology 3 ; Paul Scherrer Institut4

The High Energy Solar Spectroscopic Imager (HESSI), parts of which have been built at PSI, is a NASA satellite set to be launched by the end of January 2002. To help analyse its data, the Hessi European Data Center (HEDC) was made operational and available to the public this year.

Hessi will do imaging spectroscopy of the Sun in the 3-17000 keV range (hard x-rays and gamma-rays), with un­precedented spectral and spatial resolutions. Even though we are past this cycle's solar maximum, Hessi should still get plenty of powerful and interesting flares. As Hessi's nine sub-collimator grids modulate the received x-ray light, im­ages have to be 'reconstructed' (much as in radio interfer-ometry). This process can take anywhere from a couple of minutes (for a very basic 'back projection') to a couple of hours or more (for a tedious 'pixon' reconstruction). Add to this the fact that imaging should be done at different energy intervals of interest (thermal plasma emission, non-thermal plasma emission, gamma-ray lines,...), and that a flurry of other parameters (such as resolution, both spatial and tempo­ral) are also determinant, and one ends up with a very high amount of time taken just to check whether a single event is worth further investigations or not.

This is where the HEDC comes into play: its purpose is to generate in an automated fashion a hefty amount of quick-look data products, and assemble them in an on-line database that will allow for quick browsing and other useful services. The HEDC was setup as a collaboration between ETHZ's In­stitute of Astronomy and the Department of Computer Sci­ence. Its main uses are:

• Hessi data repository : store all Hessi raw data fits files (they come in at the rate of about 1 GB per day). Those are mirrored hourly from the Space Science Labora­tory, Berkeley, California, and are available immedi­ately to the public via anonymous ftp.

• Database : a catalog of events (solar flares, but also non-solar events such as gamma-ray bursts or electron events) and data products(images, spectra, lightcurves, at different energy ranges and accumulation times) is generated daily in an automated fashion. This database can be accessed via (any) web browser by anyone, in keeping with Hessi's open data policy. Presently, it is populated by event and data products made from sim­ulated data.

• Processing : for owners of an account on HEDC, the possibility of doing on-line processings, i.e. the recon­struction of data products, is offered. A simple HTML interface gives the possibility of using the HEDC ser­ver's CPU time to reconstruct images, lightcurves or spectra, with an easy-to-use limited set of parameters, carefully chosen amongst the forest of parameters avail­able for Hessi data product generation. Users need not remain on-line while the processing is underway,

and the results can be downloaded and/or stored into the database (and hence be accessible to other users as well).

• Miscellaneous : other useful add-ons, like a synop­tic data search engine that looks for quicklook pic­tures from other observatories, in particular the spec­trograms from ETHZ's own Phoenix-2 7m radiotéle­scope in Bleien: this ancillary data is a must-have for scientific work with Hessi data.

As the data pours in, it is being scanned for events : solar flares et altera. Even periods of relative quiet (dubbed 'quiet times') are being recorded, for finer non-solar event searches. For each event, parameters are determined and put into a ta­ble that is used for browse queries: start/end date, total num­ber of counts, maximum energy range recorded, peak count rates in 3-12, 25-50, and > 1000 keV energy bands, offset from Sun center, number of hard X-ray sources, background count rates, nightside flag, ratio of count rates between the 50-100 and the 25-50 keV energy ranges, etc.

HESSI Analyst Result

Figure 1 : Image reconstruction done at HEDC, through the simple use of a web browser (here: Netscape).

For each event, a certain number of data products are generated: those of course produce a picture, along with other parameters that can also be put into a table for later browse queries: start/end date, accumulation time, algorithm used, energy bands, time binning, pixel resolution, image di­mension, sub-collimators used, etc... All those data products can be downloaded as fits files, usable with the standard IDL-based Hessi data analysis software.

HEDC will greatly enhance scientists' ability to find suit­able data sets for research. Of course, thourough analysis will still have to be carried on with the Hessi data analysis software package.

HEDC is accessed at http://www/hedc.ethz.ch, where further informations is also available.

46

THE STATUS OF THE HESSI MISSION AND PREPARATION FOR LAUNCH

M. Fivian1, R. Henneck1, A. Mchedlishvili1, A. Zehnder1, D. Curtis2, D. Pankow3

PSI 1 - UC BERKELEY2 - GSFC GREENBELT3

HESSI is a Small Explorer NASA mission with a sin­gle instrument on a small spin-stabilized spacecraft, to be launched into a low earth orbit with a Pegasus XL rocket. Af­ter integration, the spacecraft has been over-vibrated at JPL in March 2000, which caused significant structural damage. The spacecraft had to be disassembled and all components had to be re-tested and re-qualified, some mechanical struc­tures needed repair. By end of February 2001, the spacecraft was integrated and qualified again. Because of an anomaly at a Pegasus XL launch in October 2000, the rocket needed some modifications, which delayed the HESSI launch date to June 7, 2001. On June 2, the fully integrated rocket could be shipped to Kennedy Space Center, Florida and was ready for launch. But, only one day later, NASA was launching the hypersonic test plane X-43A using a modified booster of the Pegasus XL rocket. The rocket got out of control and had to be destroyed for security reasons. Once again, HESSI was on hold and had to be shipped back to Vandenberg, Califor­nia, since the cause of the X-43A failure couldn't be found before the launch window of HESSI had to be closed around June 20. The spacecraft had to be removed from the rocket and prepared for storage for an unknown amount of time.

From August to December 2001, many tentative launch dates had been announced, but just as many questions con­cerning the launch vehicle were raised. Currently, the HESSI launch is scheduled for February 5, 2002. The Ge-detectors, which had to be cooled with liquid nitrogen for storage, have been warmed up to room temperature and the spacecraft has been mated with the Pegasus XL rocket by end of December.

Once HESSI is in orbit, all the subsystems will be switched on and taken into operation using a well defined procedure. Concerning the contribution of PSI, the imager including the aspect system will be switched on the second day of the mis­sion, followed by a calibration phase of approximately one week. After this first calibration phase, we expect to have an operational imager with a compromised accuracy of the aspect reconstruction, which will need further calibration in order to reach the goal of a pointing accuracy of 0.4 arcsec and a roll angle knowledge of 1 arcmin.

The setup procedure and calibration of the imager and the as­pect system has been carefully planned and rehearsed in the mission operation center at the Space Science Laboratory at UC-Berkeley.

Fig. 1. The fully tested and integrated HESSI spacecraft is mated on top of the Pegasus XL rocket. One fairing is already installed, the other fairing will encapsulate the spacecraft completely. One can see the three openings in the thermal shroud for the Solar Aspect System SAS.

47

THE HESSI ASPECT RECONSTRUCTION

M. Fivian1, R. Henneck1, A. Mchedlishvili1, A. Zehnder1, A. Csillaghy2, G. Hurford2, J. McTiernan2, R. Schwartz3

PSI 1 - UC BERKELEY2 - GSFC GREENBELT3

We describe the reconstruction of the aspect solution of the spin stabilized rotating (15rpm) spacecraft HESSI. The data from the subsystems, the Solar aspect system (SAS) and the roll angle system (RAS) respectively, are included in the telemetry for ground based off-line analysis. The aspect reconstruction software is fully integrated into the HESSI data analysis software and is automatically called once needed.

HESSI will image Solar flares using 9 bi-grid rotating collimators in connection with high-resolution Ge-detectors [1]. In order to reconstruct images using the modulation pat­terns seen on each of the 9 detectors, precise knowledge of the pointing and the roll angle of the spacecraft is needed. [2] Therefore, the aspect system consists of two subsystems, the Solar aspect system (SAS) and the roll angle system (RAS). The measured aspect data are sent to the aspect data proces­sor (ADP), where a compression of a factor of 1000 and a formatting into telemetry packets takes place. When analyz­ing HESSI data, the required aspect data is filtered out of the telemetry files and the aspect solution is calculated for the re­quested time range. The Aspect Solution

Star catalog Ephemerides S/C position

Aspect Solution (x,y p,t)

Figure 1: Flow char t of the aspect solution software. The Solar limbs and the Star events are fitted independently. Us­ing a Star catalog and the known geometry, the position of the Sun center in a spacecraft fixed coordinate system and a list of position angle marks can be calculated. Integration of this information, interpolation and coordinate transformation provides the needed pointing and roll angle information with respect to a inertial coordinate system.

SAS (CCD pixels around the intersection of a Solar image with three linear CCDs) and Star event data from the RAS (CCD pixels induced by passages of Star images over a lin­ear CCD). Fig. 1 shows the flow diagram of the aspect solu­tion software. The Solar limbs and the Star events are fitted independently. Knowing the geometry of all features of the SAS, the position of the Sun center, with respect to a space­craft fixed coordinate system, can be calculated. Similarly, a list of position angle marks can be generated by fitting of the Star events and subsequent comparison with a Star catalog. Integrating this information allows correcting and interpolat­ing of the roll angles. Finally, the coordinates are converted into the required pointing and roll angle format with respect to an inertial coordinate system.

Integration into the Analysis Software

The HESSI analysis software is written in IDL and is in­tegrated into the Solar Software (SSW) package, which can be downloaded from various sites [4]. Once IDL and the SSW is installed on any of the relevant computer platforms, the HESSI analysis software [5] provides a command line and a graphical user interface. The object oriented structure of the software allows fairly simple control of the given pa­rameters. Once a reference to one of the top layered objects (image, light-curve and spectrum) has been created, the con­trol parameters can be set and the data processing method can be called. In particular, an instance of the image object class inherits automatically an instance of the aspect solution object class. Therefore, the reconstruction of an image calls automatically the aspect reconstruction software. This pro­cess has been tested by a so-called end-to-end test. The sig­nals from the aspect sensors and the Ge-detectors have been simulated and were used to stimulate the data processors on the spacecraft. After having the collected data processed by the spacecraft, the antenna, the ground station and the data analysis software, the image has been reconstructed, which showed good agreement with the given input.

REFERENCES

[1] R. P. Lin et al., SPIE Proc. 3442,2 (1998).

[2] R. Henneck et al., SPIE Proc. 3765,771 (1999).

[3] M. Fivian et al, SPIE Proc. 4012,518 (2000).

[4] http://www.lmsal.com/solarsoft/

The transmitted data consists of Solar limb data from the [5] http://hessi.ssl.berkeley.edu/data/software/

48

SIMULATING HESSI'S RESPONSE TO GAMMA RAY BURSTS

C. Wigger1, M. Fivian1, W Hajdas1, D. Smith2, A. Zehnder1

PSI 1 - UC BERKELEY2

We calculated the response of the HESSI spectrometer to Gamma Ray Bursts (GRB) and Cosmic Diffuse Back­ground (CDB) using a complete mass model of the satellite. The detection threshold of GRBs was simulated for given intensities, durations and directions in space. For strong GRBs, the high energy resolution of HESSFs Ge detectors permits narrow spectral features or discrete gamma lines to be resolved in the energy spectra.

The main scientific objectives of the HESSI mission (see hessi.web.psi.ch for list of references) are dynamic solar spec­troscopy and imaging in the energy range from tens of keV to tens of MeV. In parallel, during earth occultation, the satellite will monitor large parts of the sky for non-solar science pur­poses. The observation of GRBs, going off at a rate of about one per day, is one of the most important goals, since even 30 years after their discovery, their origin still remains mys­terious. The average duration of a GRB is ss 10 s, and the average flux is sa 10~ 6 erg c m - 2 s _ 1 , both numbers varying by up to a factor of 10. The energy spectrum can be roughly approximated by dN/dE oc ( l / E ) " 1 6 .

A big advantage of HESSI, compared to other instru­ments measuring GRBs, is the high energy resolution of its germanium detectors. In our studies of HESSFs response to GRBs we use an accurate mass model of the whole space­craft, developed by UCL Berkeley and LAP PSI. Calcula­tions are performed with the help of the GEANT code from CERN. For HESSI, the expected detection rate of GRBs is about two per week. During an average GRB we expect to detect about 200 photons per second in the energy range of 50 keV to 5 MeV. The background, of either cosmic (CDB) or atmospheric origin, has a similar energy spectrum as a GRB, but its photon flux is higher than that of an average GRB. We expect a background photon rate in the order of 700 per second.

Fig. 1 shows the minimal flux of a GRB, needed to in­crease the photon rate significantly over the background rate, as a function of the time bin width.

The simulations shown in Fig. 2 was done for a GRB coming from the side and HESSI behind the earth (with re­spect to the sun). The axis of HESSI always points towards the sun. As the satellite rotates along its axis, a GRB from the side produces modulation patterns in the 9 germanium detec­tors with a period of 4s. The (simulated) number of counts in a subgroup of two detectors is plotted as a function of time. There are two comparable subgroups of detectors, each phase shifted by ss 120°. Since the direction of the burst strongly influences the amplitude of the modulation - in the worst case (i.e. a GRB coming from the back direction), the signal shows no modulation - the burst position can be determined by calculating back.

Fig. 3 shows the energy spectrum for a strong (4 x aver­age) GRB. The burst spectrum was simulated without spec­tral features. During mission operating time, we expect to detect tens of such bursts. The figure demonstrates HESSFs potential to find narrow spectral structures like red shifted annihilation lines or cyclotron absorption patterns.

1 10 time bin width [ s ]

Figure 1 : Minimal GRB flux, for a given time bin, required for detection by HESSI. Conversely, the plot also delivers the minimal time resolution for a given GRB flux.

10 12 seconds

Figure 2: Simulation of the rate modulation in a subgroup of Ge detectors caused by a strong GRB (4 x average) coming from the side. Solid Une: burst and background, dashed Une: level of background.

10'

10

++.

++++, +

' ''Ii" . i . . . . i . . . . i . . . . i . . . . i . . . . i . . . . i . . . . i . I . .h .

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 Energy in MeV

Figure 3: Energy spectrum of a strong GRB after background subtraction. (Simulation)

49

SUPERCONDUCTING TRANSITION EDGE AS ENERGY RESOLVING PHOTON DETECTOR

J. E. Olsen1, E. C. Kirk1, Ph. Lerch1, K Thomsen1, W. Hajdas1, G. C. Hilton2, M. E. Huber2, A. Zehnder1, J. M. Martinis2, H R. Ott3

P S I 1 - M S T B O U L D E R / U S A 2 , E T H Z Ü R I C H 3 ,

We are developing microcalorimeters using the supercon­ducting transition edge of thin films for application as spec­trometers. The absorbed photon energy is converted into heat which slightly warms up the calorimeter. The temperature rise, A T = E/Cv, where E is the photon energy and Cv the heat capacity, is sensed by using the sharp resistance change at the superconducting transition. The device returns to equi­librium within a time of the order of r ss Cv /g where g is the thermal link to a heat bath.

Our devices are made out of Mo/Au bilayers deposited on thin silicon nitride membranes. The proximity effect be­tween Mo and Au allows to tune the transition temperature Tc of the bilayer to be well below the Tc = 900 mK of pure Mo. The transition width measured at low current density is 1-2 mK. The abrupt resistance change near Tc is used as thermo-electrical transducer.

The thermal equilibrium situation is illustrated in Fig. 1. A stiff voltage bias is applied while the current flowing through the device is measured with a SQUID array ampli­fier. Each of these curves, measured for a given value of bias voltage, is the result of a several slow temperature cycles be­tween Tt, = 50 mK, the bath temperature and Tc = 182 mK. The steepness of these curves measures the stiffness of the voltage bias scheme that is achieved to operate this device as detector. The departure from a constant bias voltage occurs when the bath temperature is sufficiently well below Tc and the device's resistance decreases and eventually jumps into the superconducting state.

The temperature excursion AT(t) due to a a photon ab­sorption is departure from the equilibrium situation. An in­crease in electrical resistance, AR(T) = (ÔR(T)/ÔT)AT(t), transduces into a current excursion AI(T, t) measured by the SQUID. The current pulses are integrated and filtered. A his­togram of the time integral of 2000 pulses representing the energy response of ss 500 x 150 x 0.3 microns Mo/Au device is shown in Fig. 2. The width of the Ka peak is about 20 eV giving a resolving power of 290. If the device is operated with Tt, kept well below Tc, the thermal recovery time r is shortened, due to the negative electrothermal feedback. [1]

We measured the spectral density of current noise of the device at several points of operation. Excess noise is clearly present and degrades the energy resolution. We observe that the magnitude of the excess noise increases when the opera­tion point moves along the resistive transition to lower tem­perature.

10 • 1 1

% 10 o Q.

to LU I—

10

1 2

• 1 3

T b « T c

T b = T c

2 4 6 2 4 6 2

10"8 10"7 10"6

Voltage at TES [V]

Figure 1 : Equilibrium power measured in a Mo/Au transition edge sensor as a function of bias voltage. Rn = 120 mi).

200

150

100

50

Mn K„ and K,

0 LL. , 1 <.(AW),tUtl>J.t»iA»i)imt»UrV.,.il4'i,.»iU,iLj

0 1 2 3 4 5 6 7 Energy [keV]

R E F E R E N C E S

[1] A.T. Lee, P. Richards, S.W. Nam, B. Carbera, K. Irwin, Appl. Phys. Lett 69,1801 (1996).

Figure 2: Spectral response of a 500 x 150 microns Mo/Au transition edge device kept at 100 mK and irradiated by 5.9 and 6.4 keV photons.

50

SINGLE MOLECULE DETECTION OF MASSIVE MACROMOLECULES WITH SUPERCONDUCTING STRIP DETECTORS

D. Twerenbold1,2,3, D. Gerber1,3, D.Gritti1, E.C. Kirk2, Ph.Lerch2, J.-L. Vuilleumier1, A.Zehnder2

Institut de Physique Neuchâtel 1 - P S I 2 - GenSpec S A 3

In the last few years, the DNA of many species, including human, has been sequenced. This allows, in principle, to determine the primary structure of all proteins of the respective sequenced species. However, biology is more complex, especially in the higher developed species, where proteins are often posttranslationally modified. In addition, the biological activity is largely determined by networks of proteins and protein complexes.

Mass spectrometry is an important analytical technique for identifying and characterizing proteins. A commonly used method is time-of-flight mass spectrometry, where the proteins are launched by the MALDI method (matrix assisted laser desorption and ionization) using a short laser pulse (figure 1). The charged molecules are accelerated in a voltage U and enter a field-free region (~ 1 meter) with an energy given by the product of the molecule charge and the voltage U. This kinetic energy is independent of molecule mass. The mass can then be determined by the mass dependent velocity.

It is well known that the quantum efficiency of commonly used ionizing detectors decreases exponentially with decreasing velocity (increasing molecule mass). Cryogenic particle detectors are a solution to this problem [1]. The detection sensitivity is 100% on impact and independent on the molecule mass because of the calorimetric nature of the detection mechanism. This also allows to measure the total energy of the individual molecule.

We have incorporated the superconducting strip array detectors of PSI [2] into the Neuchâtel time-of-flight mass spectrometer. As the absorber is decoupled from the quasiparticle STJ sensor, a larger molecule collection area can be achieved (figure 2). In addition, the position of impact can be derived by analyzing the pulse shapes of the two correlated STJ pulses [2]. Figure 3 shows the time-of-flight histogram of a 135'000 Da (1 Da = 1 proton mass) IgG molecule obtained with the PSI strip detectors.

REFERENCES

[ 1 ] D.Twerenbold, D.Gerber, D.Gritti, Y.Gonin, A.Netuschill, F.Rossel, D.Schenker, J.-L.Vuilleumier, Proteomics 1, 66 (2001).

[2] Th.Nussbaumer, Ph.Lerch, E.C.Kirk, A.Zehnder, R.Füchslin, P.F.Meier, H.R.Ott, Phys.Rev. B 61, 9719 (2000).

sample u v | a s e r p u | s e

Ta-strip STJ cryodetector

Fig. 1: MALDI time-of-flight mass spectrometer.

protein (IgG)

epitaxial superconducting Tantal film sapphire substrate

Fig. 2: protein induced quasiparticle pulse.

50 I • 1 • 1 • 1 • 1 • 1 • 1 • 1

time-of-flight [usee]

Fig. 3 : time-of-flight spectrum of 135 kDa IgG with U=12 kV, sinapinic acid matrix and free flight distance of 1.7 meter.

51

OPERATING OF THE PROTON IRRADIATION FACILITY - CONCISE SUMMARY

W. Hajdas, F. Buri, A. Zehnder (PSI), R. Harboe-Sorensen (ESA-ESTEC)

PIF experiments in the year 2001 were further conducted in the areas NEB and PKC2. The beam time allocation of 60 shifts was fully used for ESA, Industrial and PSI related tests. Different experiments were grouped into 31 irradiation blocks resulting in 54 proton and gamma-source exposure days. Number of tests aimed to qualify and calibrate radiation monitors for forthcoming satellite missions and included SREM as well as CCD and RADFET based detectors. New studies were performed for PSI internal research and projects like LISOR and PROSCAN.

PIF experiments in the year 2001, extended through a period from 14 March to 17 December. Researches from 16 projects groups comprising industrial labs, space agencies and scientific institutes were involved in the irradiation tests. Experiments were arranged into 31 irradiation blocks of variable duration within which about 27 different types of tests and calibrations were performed. It resulted in more than 60 proton beam shifts distributed over about 50 days.

Number of PIF exper iments per month in 2001

Figure 1. Monthly use of the PIF facility in 2001.

As in the year 2000, PIF exposures utilized two irradiation areas: NEB and PCK2. The high-energy test site PKC2 proved to be both successful and convenient providing a wide range of beams specially for high intensity testing required by several projects like PROSCAN, LISOR (both from PSI) and LHC(CERN). Beginning of the bio-medical cyclotron construction works in the NA-Area in the year 2002 makes further using of the PIF PKC2 area not possible. Therefore, the facility is to be reinstalled in the GANTRY site of the NA area. A part of the NA3 beam line, upstream of the patient exposure room, can be adopted for the PIF components testing. The low energy site in the NEB area was used not only in the parasitic mode with the OPTIS but took some of free weekends for the device testing. In this area as well, it is planned to move the facility to the new beam line that allows for better optimization of the beam parameters and ensures more user and operator friendly experimental arrangement.

Table 1: Beam time and test area utilisation by PIF PKC2 NEB Total

Beam blocks 15 12 4 31

Shifts 371/2 \m 5 61

IRRADIATION EXPERIMENTS 2001 The trend of larger presence of researchers from Switzerland in PIF was seen already last year and continued during the year 2001 as well. In addition to experiments performed by different groups from CERN and Contraves Space AG, several tests were carried out in frames of PSI internal research and projects. High energy, 600 MeV beam was used to measure radioactive and poisonous isotope production rates in samples needed for the LISOR experiment for the SINQ. High intensity, 250 MeV proton exposures of different materials served for shielding optimisation and calculations of the PROSCAN project. European Space Agency (ESA) reserved beam time was used to characterise several novel radiation monitors e.g. based on the CCDs and RADFETs as well as to test radiation hardness of electronic devices. In addition, the large calibration campaign of 10 SREM monitors (developed by Contraves/ESAPSI collaboration) was successfully finished. Industrial research labs also carried out several large experiments. The Contraves Space AG tested several opto-couplers for space utilisation and OHB-Systems from Germany characterized video controllers for European part of the International Space Station -Columbus.

Table 2: Users and collaborations

No Research Institution

1 ESA / ESTEC, The Netherlands

2 PSI /LISOR (SINQ)

3 PSI / PROSCAN (Radiation Medicine)

4 ETH, Zürich

5 Contraves Space, Zürich (x2)

6 CERN, Genf (x2)

7 HIREX, France

8 OHB-Systems, Germany

9 ASTRIUM, Germany

10 Marconi Applied Technologies, UK (x2)

11 Matra BAe, UK

12 Bosch SatCom, Germany (x2)

13 Université Blaise Pascal, France

14 NMRC, Ireland

The facility obtained in the year 2001 a new, remotely controlled energy dégrader and beam profile sensitive dosimetry for the NEB area as well as computer controlled turn-table for irradiating of the test device at any angle.

52

RADIOISOTOPES PRODUCTION RATE IN HESSI SHIELDING MATERIALS

W. Hajdas, Ch.Eggel, A. Zehnder, Otmar Morath, Norbert Frei, Walter Wittwer (PSI)

Samples of natural Al, Cu, Ti, W and graded Z plates of Sn-Fe-Ta were irradiated at the PSI Proton Irradiation Facility PIF with energies typical to the radiation. Radioactive elements with half-lives ranging from minutes to tens of hours were identified using the off-line gamma ray spectrometry. Nuclear reaction production rates were obtained and compared with previous measurements as well as with calculations based on the ALICE code.

The High Energy Solar Spectroscopic Imager HESSI selected in 1997 as a NASA Small Explorer Mission SMEX, is scheduled for the launch at the beginning of 2002. Low Earth orbit of the satellite will bring an additional gamma ray background induced by trapped protons from the South Atlantic Anomaly. Although mainly low Z materials and light shielding were selected as surroundings of the HESSI germanium spectrometer, their activation is particularly relevant for probing of elements with low abundances and for non-solar science purposes like spectroscopic analysis of weak sources. Many of the proton reactions in conventional satellite shielding are still insufficiently studied in the energy ranges typical for space. Cross sections measured in PSI provide an input for forecasting of both the continuous and discrete backgrounds not only for HESSI but for other gamma ray missions too. Proton exposures experiment was performed in PIF facility and gamma spectroscopy measurements of activated samples were done with the health physics gamma spectrometer. Thin targets made of the natural compositions of shielding elements were irradiated with mono-energetic protons having energies of 50,100 and 200 MeV or using protons with wide energy spectrum (35 MeV -250 MeV), similar to that of the South Atlantic Anomaly. The following materials were tested: Al, Cu, Ti, W and a stack of Sn-Fe-Ta used as an X-ray side shielding - see PSI annex 1998. Applied radiation doses and activation analysis times allowed for determination of the radioisotopes with decay times from few minutes to tens of hours. The following table presents identified elements and their decay times for Tantalum as well as for Tungsten target, where the literature is scarce.

Table 1: Radioisotopes detected in W and Ta targets.

TUNGSTEN TANTALU M

V/i

Re-181 20.0 h W-177 2.3 h Re-182 2.7 d W-176 2.3 h

Re-182M 12.7 h W-174 29.3 m Re-179 19.5 m Ta-175 10.5 h Re-178 13.2 m Ta-174 1.2 h Re-177 14.0 m W-176 2.3 h W-177 2.3 h W-174 29.3 m

Spectra from the gamma-detector were used to determine emission Unes intensities of the radionuclides and calculate their post-exposure activities using standard gamma spectroscopy methods. Production cross sections were

determined knowing proton fluxes and exposure times together with the target mass and decay time of the isotope. For all identified isotopes and the energies that were used in the experiments, the literature cross sections were taken from the Landolt-Börnstein's "Production of Radionuclides at Intermediate Energies". The cross check with the literature data is shown in Figure 1 for 'standard'

24

p+Al—> Na reaction. In general, the agreement is within measurement errors.

p+AI -> Na

- D a t a f r o m l i t e ra tu re PIF m e a s u r e m e n t

100 150 200

Proton energy / MeV

Fig . 1: Cross section check using p+Al—> Na reaction.

The theoretical cross sections were calculated using the ALICE95 code kindly provided by F.Atchison (PSI). They were performed taking into account natural abundances of

174

target elements. An example for two radioisotopes W and Re produced on Tungsten is shown in the Figure below.

p+W-> Re —•—ALICE calc.

• experiment p+w->"V

ALICE calc. • experiment

1 0 0 1 5 0 2 0 0

Proton energy / MeV

Fig . 2 : Comparison of calculations with experiment.

As one can see, ALICE standard calculations can predict a magnitude and trend of the data, thus one can use them for rough background estimations and shielding optimisation. Data analysis from the satellite requires however more rigorous background knowledge.

53

L a b o r a t o r y f o r M u o n S p i n S p e c t r o s c o p y

Foreword

Superconductivity

Semiconductivity and Magnetism

Magnetism

Semiconductors

Developments

54

LABORATORY FOR MUON-SPIN SPECTROSCOPY

Dierk Herlach

Research at the Laboratory for Muon-Spin Spectroscopy (LMU) uses positively and (occasionally) negatively charged muons ( / i + , n~) as local magnetic probes in matter. The experimental techniques of /iSR spectroscopy (Muon-Spin .Rotation, Relaxation, Resonance) are universally applicable because polarised muons can be implanted in any material.

Muons are very sensitive probes of both static and dy­namic magnetic properties of materials: their mean lifetime of 2.2/is and gyromagnetic ratio of 2tt- 135.5 MHz/T make magnetic fields and widths of field distributions accessible in a range of ~10 / iT to several Tesla, and time scales for dynamic properties of pico- to milliseconds. As a 'light iso­tope' of the proton (mß p¿ | m p ) the positive muon can form the hydrogen-like atom Muonium ( / i + e~) which may sub­stitute for hydrogen in insulators and organic materials, thus providing a very sensitive spin label.

At present, the LMU maintains and further develops six state-of-the-art /iSR spectrometers: three for surface muons (4.2 MeV / i + ) , one for decay-channel muons (7-60 MeV / i +

or n~), an avoided-level-crossing (ALC) spectrometer, and the unique low-energy-muon beam and spectrometer (LE-/iSR) for /i+ of tunable energy between 0 and 30 keV. Two instruments are permanently installed at the 7 r M 3 beam which is equipped with a spin rotator and a beam-sharing device (MORE) that allows us to extract one muon at a time from the beam on request of one of the spectrometers, thus pro­viding unique sensitivity to small magnetic field differences and extending the measurable characteristic times into the millisecond range at one nanosecond time resolution.

Five of the instruments are operated as a User Facility for which the /iSR group provides scientific and technical sup­port. In 2001, 83 (of which 10 LE-/iSR) research proposals of groups from PSI, Swiss universities and from abroad have been active, using over 50% of the beam time allocated to all (SR and other) approved experiments at the target M and E beam lines. About 240 scientists from 22 countries have been involved in the active /iSR experiments.

One major project concerning the low energy muon pro­gram is the construction of a new surface-muon beam line in area /iE4. The detailed construction of this beam line has made very good progress in 2001, and some major com­ponents such as the large aperture quadrupoles have been ordered. Besides the various collaborations with external groups, the collaboration with other laboratories within PSI has also been fruitful. For example, in close collaboration with the low temperature facility group a new UHV sample cryostat for LE-/i+ experiments has been developed and suc­cessfully been used during the 2001 beam time. The cryostat was instrumental in the studies of non-local effects in type-I superconductors and also in the search for spontaneous sur­face magnetization in high-temperature superconductors as a consequence of broken time-reversal symmetry, where first

t e s t s w e r e p e r f o r m e d . T h e n e w d a t a - a c q u i s i t i o n s y s t e m a n d

' s l o w c o n t r o l ' o f t h e L E M a p p a r a t u s , w h i c h s i g n i f i c a n t l y i m ­

p r o v e d i t s e f f i c i e n c y a n d r e l i a b i l i t y , h a s g r e a t l y p r o f i t e d f r o m

t h e a v a i l a b i l i t y o f t h e MIDAS s o f t w a r e ( h t t p : / / m i d a s . p s i . c h / )

o r i g i n a l l y d e v e l o p e d f o r t h e ' P i o n B e t a ' e x p e r i m e n t ( s e e L a b ­

o r a t o r y f o r P a r t i c l e P h y s i c s i n t h i s v o l u m e ) .

A p r o p o s a l s u b m i t t e d b y t h e L M U t o t h e E u r o p e a n C o m ­

m i s s i o n w i t h i n t h e p r o g r a m m e ' T r a n s n a t i o n a l A c c e s s t o R e ­

s e a r c h I n f r a s t r u c t u r e s ' h a s r e c e i v e d t o p r a n k i n g b y t h e EC

e x p e r t s . S t a r t i n g i n 2002, t h e r e l a t e d f u n d i n g ( w h i c h , f o r a

p e r i o d o f 28 m o n t h s i s p r o v i d e d b y t h e F e d e r a l O f f i c e f o r

E d u c a t i o n a n d S c i e n c e b e c a u s e o f t h e d e l a y e d r a t i f i c a t i o n o f

t h e S w i s s - E U b i l a t e r a l c o n t r a c t s ) w i l l a l l o w u s t o h i r e a d d i ­

tional s t a f f a n d t o s u p p o r t a s u b s t a n t i a l n u m b e r o f r e s e a r c h e r s

f r o m t h e E U a n d a s s o c i a t e d s t a t e s .

T h e u s e r p r o g r a m s i n v o l v e a l a r g e v a r i e t y o f t o p i c s i n

c o n d e n s e d m a t t e r r e s e a r c h , t h e m a j o r i t y o f t h e p r o p o s a l s b e ­

i n g d e v o t e d t o s u p e r c o n d u c t i v i t y a n d m a g n e t i s m . E f f o r t i s

p u t o n t h e s t u d y o f n e w m a t e r i a l s s u c h a s h i g h s p i n m o l e c u l e s ,

l o w d i m e n s i o n a l m a g n e t i c s y s t e m s , o r g a n i c s u p e r c o n d u c t o r s ,

c o n d u c t i n g p o l y m e r s , l i q u i d c r y s t a l s a n d n o v e l s o l a r c e l l m a ­

t e r i a l s .

I n t h e f o l l o w i n g I ' d l i k e t o m e n t i o n j u s t a f e w o f t h e h i g h ­

l i g h t s , b u t a s t h e r e a d e r m a y s e e b y g o i n g t h r o u g h a l l 37 r e ­

p o r t s , t h e r e a r e m a n y o t h e r s i g n i f i c a n t c o n t r i b u t i o n s o f /iSR

t o t o p i c s o f c u r r e n t i n t e r e s t , s o m e o f w h i c h c l o s e l y r e l a t e d t o

t e c h n o l o g i c a l p r o b l e m s .

L o w e n e r g y m u o n s h a v e r e v e a l e d a n o n - e x p o n e n t i a l d e ­

c a y o f t h e m i c r o s c o p i c m a g n e t i c field b e n e a t h t h e s u r f a c e o f

t h e l o w - / t t y p e - I s u p e r c o n d u c t o r l e a d , a s e x p e c t e d f r o m n o n ­

l o c a l e f f e c t s w h e n t h e d i m e n s i o n o f t h e C o o p e r p a i r s i s o f t h e

o r d e r o f o r l a r g e r t h a n t h e m a g n e t i c p e n e t r a t i o n d e p t h . D i r e c t

m e a s u r e m e n t s w i t h l o w e n e r g y m u o n s o f t h e m a g n e t i c field

p e n e t r a t i n g a Y B a 2 C u 3 0 7 _ < 5 film h a v e c o n f i r m e d t h e o x y g e n

i s o t o p e e f f e c t o n t h e p e n e t r a t i o n d e p t h , w h i c h i m p l i e s t h a t

l a t t i c e v i b r a t i o n s p l a y a n i m p o r t a n t r o l e i n t h e o c c u r r e n c e o f

h i g h - T c s u p e r c o n d u c t i v i t y . F o r t h e first t i m e , b u l k /iSR h a s

s u c c e s s f u l l y b e e n u s e d t o m e a s u r e t h e field d i s t r i b u t i o n c o r ­

r e s p o n d i n g t o m o v i n g v o r t i c e s i n t h e p r e s e n c e o f a t r a n s p o r t

c u r r e n t i n a t y p e - I I s u p e r c o n d u c t o r . I n t h e H e u s l e r s y s t e m

Y b P d 2 S n , e v i d e n c e h a s b e e n f o u n d f o r a n i n t e r p l a y b e t w e e n

m a g n e t i s m a n d s u p e r c o n d u c t i v i t y b y m u o n - s p i n r e l a x a t i o n

s t u d i e s .

T h e o c c u r r e n c e o f s l o w s p i n fluctuations r e m i n i s c e n t o f

q u a n t u m c r i t i c a l d y n a m i c s o r o f d i s o r d e r e d s y s t e m s h a s b e e n

d e t e c t e d i n t h e n o n - F e r m i - l i q u i d m a t e r i a l UCus-^Pdz, a n d

a first o r d e r t r a n s i t i o n o f t h e s p i n fluctuation r a t e h a s b e e n

d i s c o v e r e d i n g e o m e t r i c a l l y f r u s t r a t e d r a r e - e a r t h o x i d e s .

A l s o , f o r t h e first t i m e a v o i d e d - l e v e l - c r o s s i n g (ALC) /iSR

h a s s u c c e s s f u l l y b e e n u s e d i n a n i n d u s t r i a l l y r e l e v a n t c o n t e x t

i n t h e field o f c h e m i s t r y .

55

A STUDY OF VORTEX MOTION IN TYPE-II SUPERCONDUCTORS USING MUON SPIN

ROTATION

D. Charalambous1, E. M. Forgan1, D. Fort1, A. J. Drew2, A. Amato3, R. Khasanov3'4

RA-01-02, BIRMINGHAM1 - St. ANDREWS 2 - PSI 3 - ZÜRICH4

The coupling of vortices to external currents and fields allows one to exert forces on them and hence access the wide field of their dynamical behaviour. We report on /xSR mea­surements from moving vortices in a polycrystalline Pb-In superconductor, carried out using the General Purpose Sur­face muon facility (GPS) at PSI.

Pb-In is a type-II superconductor with a critical temper­ature of Tc = 7K and an upper critical magnetic field of HoHC2 = 0.27 T at 4K. It is an ideal material for studying the dynamics of vortices since it exhibits very low pinning and hence a low critical current: the samples can be annealed at a high temperature in order to reduce bulk pinning and also chemically polished to reduce surface pinning.

When a transport current (density) J is applied to the sample, the vortices experience a Lorentz force F ¿ = J A B , where B is the applied magnetic field. If exceeds the pin­ning force, the vortices begin to flow. This results in energy dissipation and hence the appearance of a voltage at right angles to the direction of vortex motion, known as flux-flow voltage. The dissipation arises from relaxation of the order parameter as well as from the presence of normal currents.

Muon spin rotation (/xSR) is an ideal technique for study­ing the magnetic field probability density p(B) in a super­conductor in the mixed state[l]. We have successfully ap­plied the above technique to measure the p{B) correspond­ing to moving vortices, in the presence of a transport current. We have also calculated the expected p(B) corresponding to moving vortices and found qualitative agreement with our experimental results. Details of the calculations can be found in [2].

Our measurements were carried out using the GPS spec­trometer at PSI. A pulsed current was applied to the sample using a superconducting power supply triggered by a switch­ing circuit. The applied magnetic field was perpendicular to both the transport current and the muon beam, which was polarised so that the muon spin was at 50° to the muon mo­mentum. In order to check for the possibility of sample heat­ing due to the applied current, the data acquisition system was triggered from the current pulses using the appropriate logic, thus allowing for 'current on' and 'current off' mea­surements to be done in a single run. Within our experimen­tal resolution, no sample heating was detected and therefore the observed changes in the p(B) can be attributed to flux-flow alone.

Figure 1 shows the fittedp(£?) lineshapes as a function of the applied current. The fits were obtained using the maxi­mum entropy technique [3]. At high driving currents the /xSR lineshape is motionally narrowed, tending to a single peak at the average field, with two satellites on either side. These correspond to vortex motion along a nearest neighbour di­rection of the vortex lattice, and the central peak is due to motion incommensurate with the vortex lattice. Also visible

6A ; 7A

8A 9A "

10A 11A

y

12A :

• ' » '. i ï

A «'! •I

/ f i l i l í

//>V,I S i ! ;

"" i / / / \v' • \ .... \^ "" i

jj V .

0.125 0.13 0.135 0.14 0.145 0.15 0.155 B/T

Figure 1: Fittedp(£?) lineshapes for an applied field of 0.14 T and 2 K. The pulsed current was applied at 10 Hz.

in figure 1 are sideband peaks, the position of which depends on the vortex velocity. These result from frequency mod­ulation of the muon spin, due to the time-dependent mag­netic field distribution in the sample during flux-flow. The sidebands should therefore appear at multiples of the wash­board frequency. Our calculations show that the amplitude of the sidebands decreases very rapidly with vortex velocity and hence the peaks become very difficult to observe at high applied currents [2].

This experiment forms part of a large research program involving a variety of experimental techniques including small-angle neutron scattering (SANS), neutron spin-echo (NSE), /xSR and we are currently looking into the possibility of us­ing low-energy muons (LEM) to study vortex motion in thin films. These techniques are complementary to each other: SANS probes the structure of the moving vortex lattice, NSE can be used to measure the velocity distribution of the vor­tices in the flux-flow state, /xSR is ideal for studying the mag­netic field probability distribution and LEM could be used to examine vortex motion in ideal 2D samples.

REFERENCES

[1] S. L. Lee et al. (eds), "Muon Science" (SUSSP & Institute of Physics, Bristol, 1998).

[2] D. Charalambous et al, submitted to Phys. Rev. Lett., (2001).

[3] T. M. Riseman and E. M. Forgan, PhysicaB 289,718 (2000).

5 6

F L U X LINE LATTICE OF 3D SUPERCONDUCTORS

P. Dalmas de Réotier1, A. Yaouanc1, P. C. M. Gubbens2, S. Sakarya2 A. Amato3

RA-00-01, CEA GRENOBLE 1 - DELFT 2 - PSI 3

The discovery of high temperature superconductivity in cuprates has refocused attention on the nature of the mixed state of type-II superconductors in general. It is now apparent that the understanding of the physical properties of the vor­tex state in high Tc superconductors requires a better under­standing of that state for 3D conventional superconductors. In recent years surprising discoveries have been made for these latter compounds. The small angle neutron scatterring (SANS) technique has revealed the square flux line lattice (FLL) at high field for RENi 2 B 2 C [1] and V 3 Si [2] and the disordering of the FLL at relatively low field for RENi 2 B 2 C [3] and near the peak effect temperature for Nb [4].

Remarkably, the transverse field //SR technique has con­firmed the STM result [5] that the core size in NbSe 2 shrinks as the field increases in the low field regime [6]. In addition, this /tSR study has proven that the London penetration depth in the FLL phase is field dependent.

Here we report on the preliminary analysis of transverse field //SR measurements performed on the high-/t cubic su­perconductor V3SÍ (T c ~ 16 K). Since the measurements were done for fields not larger that 0.6 T applied along the [100] crystal field direction, the FLL is hexagonal (following SANS results [2]).

1.0 1 1 1 1 1 1 1 1 1 1

ft v 3 s í :

1 Bexl=100mT 0.8 1 T = 2K 0.6

0.4 V. © : 0.2 \ 0.0 ; J 1 . 1 1 . 1

80 100 120 140 160 Magnetic field (mT)

Figure 1: An example of a measured flux-line-lattice field density for V3SÍ at 2 K. Using a field cooling procedure, a magnetic field of 100 mT was applied along a [100] crys-tallographic direction. The field density has been computed from this spectrum using the maximum entropy algorithm. We observe the expected sharp rise of the density at low field, and a long tail at high field, typical of such a density. The sharp and small feature around 100 mT arises from muons stopped in the sample surroundings. The solid line has been computed using the parameters deduced from the fit of the corresponding /tSR spectrum presented in Fig. 2 (taking into acount only the FLL part of the depolarization function, not the background).

In Figure 1 we present a measured typical FLL field den­sity and in Figure 2 the /tSR spectrum from which this den­

sity is computed. The solid line in Figure 2 is the result of a two component fit:

a P | i p ( í ) = a s P | L L ( í ) + a b g , (1)

where the first component describes the density arising from the FLL and the second accounts for the background which is mainly due to the muons in the sample holder. ab g repre­sents less than 5 % of the whole initial asymmetry, a. In the simplest model, P ] p L ( i ) depends on four parameters: the average magnetic field, vortex core size, London penetration depth and size of disorder of the FLL which is usually ac­counted for by convoluting the theoretical FLL field density by a Gaussian function characterized by a width.

The analysis with the simple model of a set of spectra taken at 2 K using a field cooling procedure shows that the London depth is field independent, in sharp contrast to the previous finding for the lamellar compound, NbSe 2 [6]. This preliminary analysis strongly suggests that the observed field dependence of the London depth for NbSe 2 and YBa 2 Cu306 .95 [7] is related to the layered nature of these latter compounds. As expected, the core size shrinks as the field intensity is in­creased.

1—i—i—i—i—i—i—i—i—i—i—i—i—i—i—i—i—i—i—i—r

i i i i i i i i i i i i i i i i i i i i i

0.0 0.5 1.0 1.5 2.0 Time (us)

Figure 2: Transverse field /tSR spectrum recorded at 2 K after field cooling the sample in a field of 100 mT. The solid line is a fit as explained in the main text.

REFERENCES

[1] P. C. Canfield et ai, Phys. Today 51 , No. 10,40 (1998).

[2] M. Yethiraj etal, Phys. Rev. Lett. 82, 5112 (1999).

[3] M. R. Eskildsen et al, Phys. Rev. Lett. 79,487 (1997).

[4] P. L. Gammel etal., Phys. Rev. Lett. 80, 833 (1998).

[5] U. Hartmann et al., SPIE Conf. Proc. 1855,140 (1993).

[6] J. E. Sonier etal., Phys. Rev. Lett. 79,1742 (1997).

[7] J. E. Sonier et al, Phys. Rev. Lett. 83,4156 (1999).

57

MAGNETIC FIELD PROFILE BENEATH THE SURFACE OF Pb AND Nb FILMS

E. Morenzoni1, N. Garifianov1'5, R. Khasanov1'2, H. Luetkens1'4, T. Prokscha1, A. Suter1, M. Horisberger1, E. Kirk1, E. M. Forgan3, D. Ucko3

PSI 1 - ZÜRICH 2 - BIRMINGHAM3 - BRAUNSCHWEIG4 - KAZAN 5

Low-energy /xSR (LE-/xSR) is the most direct technique which can provide the functional dependence of the magnetic field B(z) as a function of the distance z from the surface of a sample. A recent measurement showed that in a high k type II superconductor such as YBa2Cu307_,5 in the Meiss­ner state the microscopic magnetic field decays exponentially with depth z [1]:

E(z) ~ e x p ( - z / A ) . (1)

This measurement provided also the first absolute and model-independent determination of the London penetration length A. In general, however, B(z) does not vary in a simple way with z. The exponential decay of the magnetic field beneath the surface in the Meissner state is an approximation, which is no longer valid if the dimension of the Cooper pairs £ is of the order or larger than A. In this case a non-local re­lation between vector potential and current lead to various effects: the range of magnetic penetration is increased; the field profile deviates from an exponential dependence and for larger depths z the magnetic induction may even change its sign [2, 3]. These effects are especially pronounced in ex­treme type I superconductors such as Al (k = 0.03) and Sn (k = 0.23). But also Pb with k = 0.48 is a possible candi­date for non-exponential behavior, since calculations predict the appearence of effects already for k ~ 1 [2]. In this sys­tem non-local effects have been searched for in the past by polarized neutron reflectometry where one uses the fact that changes of the magnetic induction at the surface will alter the relative specular reflection probability of neutrons polarized parallel or antiparallel to B. However, non-local corrections to the exponential decay of magnetic induction in lead have been shown to be beyond the sensitivity of polarized neutron reflectometry [4]. This is because it is not possible to derive B(z) directly from the measured reflectivities. The informa­tion is obtained instead by calculating these quantities under different model assumptions. By contrast polarized low en­ergy muons of variable energy, which can be implanted in a sample at various depths, are depth dependent magnetic microprobes whose precession spectrum directly deliver the value of the local field.

Muons of energies between 1.5 keV and 28 keV were implanted in a 500-nm thick, zero field cooled Pb film at var­ious temperatures below T c . A field of ~ 100 G was applied parallel to the surface of the film and transverse to the initial muon spin polarization. For a comparison we also investi­

gated a Nb film of 300 nm thickness which has a A com­parable with Pb but where, due to the larger k of 1.28 non­local effects are expected to be suppressed. The films were deposited by a sputtering technique on a quarz (Pb) or sap­phire crystal (Nb). Figure 1 plots the average local magnetic field obtained from the muon spin precession spectrum ver­sus the average implantation depth at different temperatures. Whereas for Nb (not shown) at T = 2.5 K an exponential de­pendence of B(z) is found, for Pb, a reduced magnetic field decay over a depth of the order of the coherence length and an overall non-exponential shape are observed, in qualitative accordance with the prediction of reduced surface screening currents due to non-local effects and deviations from London theory.

1 « 1 •

P b 500 n m .

-•— 2.5 K o 5.0 K

-A— 6.0 K - A — 6.6 K -V - 6.8 K -0 40 80 120 160

Depth (nm)

Figure 1 : Mean magnetic induction versus depth for a 500-nm thick Pb film (with T c = 7.1 K) as function of tempera­ture.

REFERENCES

[1] T. Jacksonera/., Phys. Rev. Lett. 84,4958 (2000).

[2] J. Halbritter, Z. Phys. 243, 201 (1971).

[3] K. E. Drangeid and R. Sommerhalder, Phys. Rev. Lett. 8,467 (1962).

[4] M. P. Nutley er al., Phys. Rev. B 49,15789 (1994).

58

LOW-ENERGY //SR INVESTIGATION OF THE OXYGEN ISOTOPE EFFECT ON THE MAGNETIC PENETRATION DEPTH OF Y B a 2 C u 3 0 7 _ , 5

R. Khasanov1,2, K. Conder2, E. M. Forgan3, N. Garifianov2,4, H. Keller1, H. Luetkens2,5, E. Morenzoni2, T. Prokscha2, A. Suter2

ZÜRICH1 - PSI 2 - BIRMINGHAM3 - KAZAN 4 - BRAUNSCHWEIG5

The pairing mechanism responsible for high-temperature superconductivity (HTSC) remains elusive in spite of the fact that many models have been proposed since its discovery. A fundamental question is whether lattice effects are relevant for the occurrence of high-temperature superconductivity. In order to clarify this point a large number of isotope-effect studies were performed since 1987. It was established that in HTSC - in contrast to conventional (BCS) superconductors where the isotope effect only changes the transition temper­ature T c - the effective charge carrier mass is also isotope dependent. This provides evidence that electron-phonon cou­pling is present in cuprates and that the charge carriers have polaronic character [1,2].

For cuprate superconductors (clean limit) the in-plane pen­etration depth A0fc is simply given by A~fc

2(0) oc ns/m*ab, where ns is the superconducting charge carrier density, and m*ab is the in-plane effective mass of the superconducting charge carriers. Consequently, it follows

Ans/ns - Am*ab/m*ab. (1) AA o - f c

2 (0)/A o - f c

2 (0)

Therefore, a possible mass dependence of m*ab can be tested by investigating the isotope effect on A0¡,, provided that the contribution of ns to the total isotope shift is known. There are several independent experiments, that clearly show that the ns change during isotope exchange is very small [3,4].

Low-energy /xSR (LE-/xSR) represents one of the most direct techniques for A measurements. It allows to profile directly the magnetic field beneath the surface of a supercon­ductor in the Meissner state, with a depth resolution of a few nanometers. It is well known that, for superconductors in the clean limit, a magnetic field applied parallel to the surface of a semi-infinite slab decays exponentially with depth z:

B(z) = B0exp(-z/Xab). (2)

For a film with finite thickness 2t and with flux penetrating from both sides Eq. 2 is modified to

B(z) =B0->sh[(t - z)/Xah]

COSll(t/Xab) (3)

During the experiments the magnetic field was applied parallel to the surface of a c-axis oriented superconducting 600-nm thick YBa2Cu3Û7 film after zero field cooling the film to 5 K. In this geometry, currents flowing in the ab planes determine the profile along the crystal c-axis of the magnetic field inside the film. Muons were implanted at depths from 40 - 150 nm by varying the energy of the incident muons from 5 to 30 keV.

Figure 1 shows the field decay in the Meissner state for an YBa2Cu3Û7 thin film sample with two oxygen isotopes. One can see that for the 1 6 0 sample the magnetic field inside

of the sample decays faster than for the 1 8 0 one. According to the formula (3) this means that Xab for the 1 6 O sample is smaller than for the 1 8 O sample. The calculations of the isotope shift in A a f c give AXab/Xab = 2.5(10)% for T = 4 K and 2.7(15)% for T = 30 K.

10

9

8

p CD 6

- I ' 1 1— —1 '— (a)

T=4K •

\

\ J.(1*O)=151.2(0.8)nm X(1,O)=155.0(1.5)nm

Am=2.5(10)% \

- 1 1 1 1 1 (b)

\ T : =30K-\ Û ,6o

\ * , . 0 .

X('*O)=160.0(2.4)nm V • l(1,0)=164.3(1.8)nm \ Am=2.7(15)% \ 0 50 100

Depth (nm) 50 100

Depth (nm)

Figure 1 : Values of field versus depth for the samples with two different oxygen isotope 1 6 0 and 1 8 0 . (a): T = 4 K and (b): T = 30 K(b). Solid Unes represent fits to Eq. (3).

Our experiments provide strong evidence for an isotope effect on the magnetic penetration depth in optimally doped cuprate superconductors. This implies that lattice vibrations play an important role in the occurrence of high-T c super­conductivity.

REFERENCES

[1] Proc. Int. Workshop on Anharmonic Properties of High- Tc Cuprates, ed. D. Mihailovic, G. Ruani, E. Kaldis, and K. A. Müller (World Scientific, Singapore, 1994), 118.

[2] A. S. Alexandrov and N. F. Mott, Int. J. Mod. Phys. 8, 2075 (1994).

[3] G. M. Zhao et ai, J. Phys.: Condens. Matter 10,9055 (1998).

[4] J. Hofer et al., Phys. Rev. Lett. 184,4192 (2000).

59

EXPERIMENTS ON THE MAGNETIC FLUX LINE LATTICE IN AN ANTIDOT PATTERNED NIOBIUM FILM USING THE PSI LOW-ENERGY MUON FACILITY

E. Forgan1, D. Ucko1, N. Garifianov2*5, R. Khasanov2^, H. Luetkens2*3', E. Morenzoni2, T. Prokscha2, A. Suter2, H. P. Weber2, V. Metlushko6

BIRMINGHAM1 - PSI 2 - BRAUNSCHWEIG3 - ZÜRICH 4 - KAZAN 5 - ILLINOIS6

Low-energy /xSR holds all the advantages of conventional pSR in the study of superconductors and flux lattices, and in addition enables the study of thin film samples, something which is impossible with high energy muons. A study of fluxline structures on a thin film of niobium patterned with a square lattice of holes has been done at the PSI low-energy muon beamline at 7rE3. The sample was prepared at the Uni­versity of Illinois at Chicago.

Previous magnetic force microscopy work has been done on the vortex states in niobium [1, 2]. Simulation studies have also been made [3], studying the effects of both square and triangular lattices. These studies have found not only that fluxlines initially appear at the artificial pinning sites, but that above a certain commensurate field interstitial fluxlines appear between the pinning sites or multiple fluxlines at the pinning sites.

A patterned Nb film, 100 nm thick, with circular holes of ~ 350 nm diameter spaced 1000 nm apart from centre to centre in a square lattice, was covered with a silver layer 70 nm thick. The purpose of this configuration was to have the implanted muons land in the silver and measure the field due to the fluxlines of the vortex lattice. The Nb film was mounted perpendicular to the direction of the beam, with the equipment in perpendicular field (out of the plane) direction. Magnetic fields were applied at integer (n) and half-integer (m/2) multiples of the matching field of one flux quantum per hole, which is 21 G for this film.

2 K, 84 G

60 65 70 75 80 85 90 95 100

Field (G)

Figure 1 : Background corrected Maximum Entropy plot for an applied integer multiple of the matching field.

2 K, 92 G 80 L 1 1 1 1 I 1 1 1 1 I 1 1 1 1 I 1 1 1 1 I 1 1 1 1 I

CÛ

75 80 85 90 95 100 105 110

Field (G)

Figure 2: Background corrected Maximum Entropy plot for an applied half-integer multiple of the matching field.

For applied fields that are an integer multiple of the match­ing field, the strongest part of the field distribution due to the flux lines was observed at a lower field than the back­ground peak. For applied fields a half-integer multiple of the characteristic field, peaks were observed at both sides of the background peak, which is due to an uneven flux quan­tum occupation at the holes (pinning centres). In the figures shown, the background peak has been artificially reduced in order to emphasise the side peaks. It was noted that higher fields (corresponding to higher values of n and m) increased the separation of the side peaks as well as their relative in­tensities. Detailed analysis is in progress.

REFERENCES

[1] V. Metlushkoeia/., Interstitial flux phases in a superconducting niobium film with a square lattice of artificial pinning sites, Phys. Rev. B 60, R12585 (1999).

[2] M. Roseman et al., Flux lattice imaging of a patterned niobium thin film, J. Appl. Phys. 89, 6787 (2001).

[3] C. Reichhardt et al, Commensurate and incommensu­rate vortex states in superconductors with periodic pin­ning arrays, Phys. Rev. B 57,7937 (1998).

60

EXOTIC ANISOTROPIC SUPERCONDUCTORS

S. L. Lee1, A. J. Drew1, U. Divikar1, F. L. Pratt2, E. M. Forgan3, D. Charalambous3, H. Keller4, F. Y. Ogrin5

RA-94-04, ST. ANDREWS 1 -ISIS 2 -BIRMINGHAM3 -ZÜRICH4 -EXETER5

While at first sight there may appear to be little resem­blance between the highly anisotropic model organic su­perconductor /t-(ET)2Cu(SCN)2 (ET-Cu) (T c ~ 10 K) and the high-T c BSCCO, there are in fact an astonishing num­ber of similarities. Both are highly layered superconducting systems, with anisotropy ratios in excess of 100 and layer spacings ~ 15 Â. We have previously demonstrated that de­spite its low Tc, the vortex lattice in ET-Cu is thermally dis­rupted above a melting temperature which lies well below Tc

[1, 2, 3 ,4, 5]. This is possible because of the high anisotropy combined with the very long penetration depth À ~ 6000 Â.

Subtle changes in the structure of ET-Cu crystals with the same nominal composition can produce radical changes in the vortex behaviour. This should not be mistaken for dif­ferences of sample'quality', but rather that different prepara­tions can produce slight distortions which change the overlap of molecular orbitals which provide the (weak) conduction path between the planes of these layered conductors. During the beamtime we were able to characterise the melting Unes for two sets of samples, confirming our earUer suggestions that these are vortex systems which represent two different classes of behaviour. While both have extremely similar T c's and penetration depths, their anisotropics are radically dif­ferent. This changes the ratio of the penetration depth to the Josephson length, so that each belongs to a class of materials where Josephson coupUng is either significant or insignifi­cant in controlling vortex behaviour. The disorder crossover fields are consequently very different, but moreover so are the forms of the melting Unes, which show generic trends ex­pected from each class. This work is currently in preparation for publication. Studies of ET-Cu have also revealed some extremely interesting angular dependent variations of the line width in this system, which we believe to reflect the low field instabiüties of tilted vortices in this highly anisotropic sys­tem.

On the LTF we have carried out work on the BETS salt k-(BEDT-TSF)2FeCl4, which orders antiferromagnetically at ~ 0.5 K, followed by the onset of superconducting order at ~ 0.1 K. We were able to observe both well defined oscil­lations arising from the ordered ferromagnetic moments in addition to the onset of the superconducting transition, from which we could obtain some preUminary information [6].

We also performed low temperature measurements on LaNiSn, which is a structural analogue of the 'Kondo in­sulator' CeNiSn. There has been considerable interest in CeNiSn, since NMR and heat capacity studies suggest ev­idence for a pseudogap with a residual density of states around the Fermi level, as predicted theoretically by Ikeda and Miyake [7]. For pure crystals the system shows increas­ingly metallic behaviour with increasing purity, which makes

it distinct from archetypal Kondo insulators, which show in­creasing low-temperature resistance ratio with increasing pu­rity. The important questions associated with the pseudo-gap in CeNiSn involve the hybridisation between the 4f electrons and the conduction electrons in the orthorhombic structure. Thus LaNiSn is of interest in that it is a non-magnetic ana­logue of this system. The existence of superconductivity has recently been reported in LaNiSn [8], with a Tc ~ 0.65 K.

This year we performed some preUminary measurements on a large single crystal of this system, finding an upper crit­ical field value of i î C 2 (0) s¿ 15 mT and an i î C l (o) ~ 6 mT. The pentration depth is very long (~ 3000 Â), so that the Uneshapes are narrow even well below HC2(T). We have uncovered a number of interesting features of this system, including some novel behaviour concerning the interplay of the intermediate state, Meissner state and mixed state around HcAn

REFERENCES

[1] S. L. Lee, S. J. Blundell, F. L. Pratt, C. M. Aegerter, P. A. Pattenden, K. H. Chow, E. M. Forgan, T. Sasaki, M. Hunt, W. Hayes, H. Keller, Phys. Rev. Lett. 79,1563 (1997).

[2] C. Ager, S. L. Lee, C. M. Aegerter, F. L. Pratt, S. J. Blundell, S. H. Lloyd, T. Sasaki, E. M. Forgan and H. Keller, J. Mag. Mag. Mat. 177-181,561 (1998).

[3] S. J. Blundell, S. L. Lee, F. L. Pratt, C. M. Aegerter, Th. Jestädt, B. W. Lovett, C. Ager, T. Sasaki, V. N. Laukhin, E. M. Forgan and W. Hayes, Synth. Met. 103,1925 (1999).

[4] F. L. Pratt, S. J. Blundell, A. Husmann, I. M. Marshall, B. W. Lovett, W. Hayes, S. L. Lee, C. Ager, F. Y. Ogrin, T. Sasaki, N. Toyota, K. Kanoda, V. N. Laukhin, E. Laukhin, I. Watanabe and K. Nagamine, Physica B 289-290, 396 (2000).

[5] F. L. Pratt, S. L. Lee, C. M. Aegerter, C. Ager, S. H. Lloyd, S. J. Blundell, F. Y. Ogrin, E. M. Forgan, H. Keller, W. Hayes, T. Sasaki, N. Toyota, S. Endo, Synth. Met. 120,1015 (2001).

[6] F. L. Pratt, S. L. Lee, S. J. Blundell, I. M. Marshall, H. Uozakid and N. Toyotad, accepted for publication in Physica B, (2002).

[7] H. Ikeda and K. Miyake, J. Phys. Soc. Jpn. 65, 1769 (1996).

[8] Y. Echizen etat, Solid State Commun. I l l , 153 (1999).

61

MAGNETISM AND SUPERCONDUCTIVITY IN 1212-TYPE RUTHENOCUPRATES

P. W. Klamut1'2, A. Shengelaya3, R. Khasanov3A, I. Savic5, B. Dabrowski1, H. Keller3

RA-97-12, NORTHERN ILLINOIS1 - INTIBS WROCLAW2 - ZÜRICH 3 - PSI 4 - BEOGRAD 5

We have investigated the magnetic and superconducting properties of R u i - ^ S ^ R E Q ^ + z O g - ^ , RuSr2RECu20g (RE = Gd, Eu) and RuS^Gdn.gCeo.iC^Og. The inves­tigated compounds belong to the recently reported series of RuSraGdi-yCeyCuaOg [1] a n d R u i - Ä G d C u a + z O g ^ [2] that in the RuSr2GdCu2 0g weak-ferromagnetic super­conductor parent structure [3] realize electron (y) and hole (x) doping. Measured /xSR characteristics, when combined with the results of magnetic and transport experiments allow us to propose the phase diagram for different hole doping in the 1212-type ruthenocuprates (see Fig. 1). The T N line

200

I—

hole doping — * -Figure 1: The phase diagramm of Ru 1212 system. The T N and T M lines reflects the phase transition to the magneti­cally ordered state, open triangles from zero-field (ZF) /xSR and closed triangles - from magnetization measurements (the asymmetry factors in /xSR measurements confirmed the mag­netic response of the whole volume of the samples). The y m a x j j n e r e p r e s e n t s the superconducting transition temper­ature.

reflects the phase transition to the AFM canted state in the Ru spin system. The origin of the magnetically ordered state found below T M for superconducting x = 0.1, 0.3 and 0.4, although tentatively ascribed to the response of Cu/Ru sub-lattices, remains a subject open for investigation. Other ex­periments indicate an increase of the Cu valence with x [4] and reveal that the properties of the series are consistent with that of the underdoped HTSC.

Recently, the superconductivity has been also reported in the Eu based analogue of Rui_ xSr2GdCu2+ xOg_ z (see Fig. 2). The temperature dependence of a shows an upturn at 60 K due to the superconducting mixed state. The <jsc

(superconducting) at T = 0 can be inferred by cutting off the magnetic contribution raised below 5K and scales well with T C according to the universal Uemura relation for uderdoped HTSC compounds.

The modified synthesis of RuSr2RECu2 0g lead us to non-superconducting materials for both Eu and Gd compo­unds [4]. Subsequent oxygen annealing, analogous to the conditions presented in [3], results in the inducement of su-

Figure 2: The gaussian relaxation rate a vs. T for a super­conducting ( T C = 60 K) sample of R u o . 6 S R 2 E U C U 2 . 4 0 g _ z . Transverse-field /xSR (2 kOe).

perconductivity with T C up to 45 K. As can be seen from Fig. 3, the internal field is about 10% larger in the supercon­ducting material, which simultaneously has a slightly lower T N . This is in agreement with the magnetization measure­ments performed on our superconducting and non-supercon­ducting samples of R U S R 2 G D C U 2 0 g . The low tempera­ture increase of i í ¡ n t observed for R u S r 2 G D C U 2 0 g (Fig. 3) should be associated with the AFM transition present in G d 3 + sublattice and is absent for the analogue Eu compound.

800 ••-••-•SC RuSr2GdCu208 [3] —•— non-SC RuSr„GdCu,00

600

O 1 400 -

200 -

T(K) Figure 3: Temperature dependencies of the internal field (Hint) for non-superconducting samples of RuSr2GdCu2 0g (closed circles) and RuSr2EuCu2 0g (open circles) (ZF /xSR). Closed squares - data for superconducting RuSr2GdCu20g from Ref. [3].

REFERENCES

[1] P. W. Klamut et al, Physica C 350, 24 (2001).

[2] P. W. Klamut et al, Phys. Rev. B 63, 224512 (2001).

[3] C. Bernhard et al, Phys. Rev. B 59,14099 (1999).

[4] P. W. Klamut et al, Physica C 364, 313 (2001).

62

COEXISTENCE OF MAGNETISM AND SUPERCONDUCTIVITY IN R^Ceo .eRuSraCuaO

(R = Eu AND Gd)

A. Shengelaya1, R. Khasanov1'2, H. Keller1, E. Morenzoni2, K Conder2,1. Feiner3, U. Asaf, and I. M. Savic4

RA-90-07, ZÜRICH1 - PSI 2 - JERUSALEM3 - BEOGRAD 4

The hybrid ruthenate-cuprates R i . 4 C e n . 6 R u S r 2 C u 2 0 i o (Ru-1222) and R u S r 2 R C u 2 0 8 (Ru-1212) (R= Sm, Eu, and Gd) have recently attracted much attention because of the co­existence of superconductivity and long-range magnetic or­der [1, 2]. These compounds have a layered structure with alternating CuC>2 and RuC-2 layers. It seems that supercon­ductivity takes place in the Q1O2 layers like in the high-T c

cuprates, whereas magnetic order takes place in the RuC-2 planes. Till now most of the reports have focused on a Ru-1212 phase, where the magnetic transition is observed at Tm

= 133 K and superconductivity sets in at T c=35 K. In the present experiment we focused our attention on a Ru-1222 phase, which is actually the first ruthenate-cuprate where the coexistence of superconductivity and magnetism was found [1]. Both Ru-1212 and Ru-1222 contain similar C u 0 2 and RuC>2 planes. However, in Ru-1222 it is possible to vary the charge carrier concentration in contrast to Ru-1212 which is a stoichiometric compound. Recently, a jump in the specific heat at Tc was observed in Ru-1222, confirming bulk super­conductivity [3]. However, it remains to demonstrate that magnetic order also has bulk character, in order to infer the microscopic coexistence of magnetism and superconductiv­ity. To answer this question we studied Ru-1222 using ZF pSR. The pSR technique is especially suitable for such a study since the positive muon is an extremely sensitive local probe to detect internal magnetic fields and their distribution. In addition, as a real-space probe, pSR can determine the or­dered volume fraction.

Below Tm=90 K Ru-1222 samples show damped oscil­lations due to muon-spin precession in local magnetic fields. A clear oscillation observed in ZF-/1SR spectra implies that the muons sense a well defined internal magnetic field. The pSR spectra were analyzed using the standard function:

A(t) = A1exp(-\t) + A2exp{-At)cos(j^B^t+^), (1)

where 7 M = 851.4 Mrad s _ 1 T _ 1 is the gyromagnetic ratio of the positive muon, £ M the average static internal magnetic field at the muon site.

We observed that a fit to Eq. (1) with a single Bß resulted in a very poor agreement with the spectra. We found that two different local magnetic fields £ M l and Bm satisfactorily fit the spectra below 90 K. This was further confirmed by a Fourier transformation of the time spectra, where two peaks in the magnetic field distribution were observed. Figure 1 presents the internal magnetic fields £ M l and Bm as a func­tion of temperature for the Eu Ru-1222 sample. One can see from Fig. 1 that there is no strong anomaly at the supercon­ducting transition temperature T c =40 K.

70

0 20 40 60 80 100 T(K)

Figure 1 : Temperature dependence of the internal magnetic fields in Eui .4Cen.6RuSr 2 Cu20io at the two muon sites £ M l

and Bm. The solid lines represent fitted curves to the power law B^ (T) = B^ (0)(1 - T/Tm)n*.

It is important to determine whether this magnetic order has a bulk character or occurs only in a small part of the sam­ple. It is possible to extract the volume fraction of the mag­netically ordered phase from the amplitude of the oscillating component of the ZF pSR spectra. Fitting the ZF pSR spec­tra in the magnetic state with Eq. (1), we found that the size of the non-oscillatory and oscillatory components Ai and Ai correspond to l /3P ( t = 0) and 2/3P(t = 0), respectively. This shows that the entire sample volume is magnetically or­dered.

Our ZF pSR results provide conclusive evidence of a uni­form and homogeneous magnetically ordered state in the en­tire sample volume below T T O=90 K in the Eu and Gd Ru-1222 samples. Below T c =40 K the samples become super­conducting without a significant change of the magnetic or­der. Taking into account the specific-heat measurements of Ru-1222 demonstrating bulk superconductivity [3] and the present results, we conclude the microscopic coexistense of magnetism and superconductivity in these ruthenate-cuprates.

REFERENCES

[1] I. Feiner et al, Phys. Rev. B 55, R3374 (1997).

[2] C. Bernhard et al, Phys. Rev. B 59,14099 (1999).

[3] X. H.Chen et al, J. Phys.: Condens. Matter 12,10561 (2000).

63

COEXISTENCE OF SUPERCONDUCTIVITY AND ANTIFERROMAGNETISM IN YbPd 2 Sn

A. Amato, B. Roessli

RA-01-04, PSI

The search for novel pairing mechanisms for the forma­tion of Cooper pairs in superconducting systems has recently received a large stimulation from the discovery of materials exhibiting a coexistence of superconductivity and magnetism (see for example [1]).

One actively pursued avenue, both theoretically and ex­perimentally, is the possibility that the pairing mechanism can be mediated by magnetic fluctuations rather than by phonons. While static magnetic order disappears upon dop­ing in the sc phase of high-T c materials, it pertains in heavy fermion compounds like UPd2Al3, U N Í 2 A I 3 , U R U 2 S Í 2 , and U G e 2 . To clarify the interplay between magnetism and su­perconductivity, it is therefore essential to characterise the magnetic response in such compounds. In particular, a key experimental issue is to show if, in contrast with the Chevrel phases, the same electronic states which become magneti­cally ordered also participate in superconductivity.

Recently [3], coexistence of superconductivity and mag­netic order has been reported for the cubic Heusler com­pounds ErPd2Sn and YbPd 2Sn. YbPd 2Sn is a special case as antiferromagnetism sets in only at very low tempera­tures deep in the superconducting phase. Namely, whereas YbPd2Sn becomes superconducting at T c ~ 2.3 K, a com­mensurate magnetic structure with propagation vector [001] (and Yb-static moments at saturation ris ~ lAriB) is found by neutron diffraction only below T ~ 0.22 K.

The first riSR results obtained in 2001 can be summa­rized as follows. In the zero-field (ZF) spectra, the occur­rence of magnetic fluctuations is clearly seen by cooling the sample below 40 K (see Fig. 1). It is evidenced by a sizeable increase of the exponential depolarisation rate. The dynam­ical character of the magnetic fluctuations is demonstrated by longitudinal-field (LF) measurements where no sizeable influence of the externally applied field (6 kOe) could be de­tected in the paramagnetic state. Very recent neutron mea­surements [3] confirm the presence of q-independent (i.e. on-site) quasi-elastic magnetic fluctuations which show a dra­matic increase below about 40K.

Of importance is the additional increase of the muon de-polarisation rate when cooling the sample into the supercon­ducting state (see Fig. 1). This observation indicates a link between the superconducting order parameter and the mag­netic fluctuations. Interestingly, no sizeable modification of the neutron scattering signal could be observed below this temperature, which points to an increase of the characteristic fluctuation time rather than a change of the involved mag­netic moments.

Measurements under longitudinal fields also demonstrate the interplay between magnetic fluctuations and supercon­ductivity. As shown in Fig. 2, the increase of the muon depo­larization rate below T c is cancelled when the applied longi­tudinal field is higher than B c 2 , i.e. when the superconduct­ing state is suppressed by the applied field.

30

Temperature ( K )

Figure 1: Muon depolarization rate obtained in ZF on YbPd2Sn. Note the increase below Tc

The muSR studies performed to date suggest the impor­tance of the magnetic fluctuations for the superconducting phase occuring below 2.3 K. This points to an unconventional superconducting state characterised by non-phonon pairing mechanism and possibly an non-spherically symmetric su­perconducting order parameter (i.e. L ^ 0).

25 r 1

YbPd2Sn Bc2

N - 2 0 : T 1 .8K

5 -

0°00 0.01 0.02 0.03 0.04 0.05 0.06 Field ( T )

Figure 2: LF dependence of the muon depolarization rate measured at 1.8 K. Note the drop when Bext > -BC2

REFERENCES

[1] N. D. Mathur et al., Nature 394, 39 (1998).

[2] Y. Aokietal.,J. Magn.Magn. Mat. 177-181,559 (1998).

[3] B. Roessli et al., to be published.

64

STUDYING THE MAGNETIC INSTABILITY IN HEAVY-FERMION (U,Th)Pt 3

M. J. Graf1'8, A. de Visser2, C. P. Opeil1, J. C. Cooley3, J. L. Smith3, A. Amato4, C. Baines4, F. N. Gygax5, A. Schenck5

RA-01-06, BOSTON 1 - AMSTERDAM 2 - LANL 3 - PSI 4 - ETH ZÜRICH5

In the heavy-electron system U P t 3 magnetism and super­conductivity are closely related. Recently, we utilized /xSR measurements to demonstrate that the phase diagram of the pseudobinary compounds U ( P t i _ x P d x ) 3 shows an antiferro­magnetic quantum critical point at x c , a / = 0.006 [1]. The critical Pd concentration for the suppression of superconduc­tivity is identical: x C j S C = x c , a / = 0.006 (see Fig. 1). The existence of this mutual critical point in the phase diagram provides new evidence for pairing mediated by ferromag­netic spin fluctuations. To test this conjecture, it is impor­tant to know if the competition between antiferromagnetism and superconductivity is a general property of U P t 3 . In this respect Th is an excellent dopant, as it also induces static antiferromagnetic order.

The aim of these experiments is to investigate the emer­gence of magnetic order in U P t 3 doped by Th, and its rela­tionship to the suppression of superconductivity. Polycrys-talline ( U i _ x T h x ) P t 3 samples were prepared with x = 0, 0.002,0.005,0.01,0.02, and 0.05. During two days of beam time, zero-field measurements were made on x = 0.01 and 0.02 samples (GPS), and the 0.005 sample was studied in a 100 G transverse field using the LTE Other samples were studied resistively at Boston College.

The observed depolarization for samples with x = 0.02 and 0.01 is well-described by the same multicomponent func­tion used for U(Pt,Pd)3 [2]. The x = 0.02 sample exhibits spontaneous oscillations (Fig. 2) for T < T n = 4.9 K. For x = 0.01 , strong depolarization sets in below T n = 3.4 K, and heavily-damped oscillations were observed at 2 K. For x = 0.005, no signature of magnetic ordering is observed in transverse field data taken in the LTF (0.05 K < T < 1.2 K); a weak increase in the depolarization rate is observed, however, at the superconducting transition temperature T c = 0.24 K, as reported for UPt 3 [3].

Magnetic ordering and superconductivity do not appear to coexist for any of the samples studied, consistent with our results for U i P t i - ^ P d ^ . However, as seen in Fig. 1, T n is still rather large for x = 0.01, and one can expect dramatic changes for samples with 0.005 < x < 0.01 if antiferromag­netism and superconductivity are to be mutually exclusive. Studies in this range of concentrations will provide a strin­gent test of the mutual quantum critical point scenario, and may also provide important insights into the distinction be­tween conventional AFM and the anomalous small-moment AFM which coexists with superconductivity. Samples with x = 0.006, 0.007, 0.008, and 0.009 are now being prepared for this study.

5 -

4 -

3 -z Ü

r- 2 -

1 :

0.0 0.5 1.0 1.5 2.0

Impurity Concentration (at. %)

Figure 1: Phase diagram for U ( P t i _ x P d x ) 3 (open circles) and ( U i _ x T h x ) P t 3 (filled circles).

N I

o c <D 3 O"

2 3 4 5

Temperature (K)

Figure 2: Spontaneous precession frequency versus temper­ature for U o . 9 8 T h 0 . o 2 P t 3 -

R E F E R E N C E S

[ 1 ] A. de Visser et al., Phys. Rev. Lett. 85, 3005 (2000).

[2] R. J. Keizer et ai, J. Phys.: Condens. Matter 11 , 8591 (1999).

[3] A. Amato, Rev. Mod. Phys. 69,1119 (1997), and references therein.

65

MAGNETIC-SUPERCONDUCTING MULTILAYERS

A. Drew1, S. L. Lee1 E. Morenzoni2, T. Prokscha2, H. Luetkens2'3, A. Suter2, R. Khasanov2'4, N. Garifianov2'5

ST. ANDREWS 1 - PSI 2 - BRAUNSCHWEIG3 - ZÜRICH 4 - KAZAN 5

The competition between superconducting and magnetic order is a problem of longstanding and continuing interest in condensed matter physics. At a simple level, ferromagnetic order, which will tend to polarise the conduction electrons via the exchange interaction, will not be conducive to the ex­istence of Cooper pairs within a conventional BCS scenario, where electrons form spin singlet pairs. This 'pair breaking' effect will tend to destroy superconductivity, and the coexis­tence of the two forms of order is only found in a relatively small number of compounds. In systems where this coex­istence occurs among the same conduction electrons, this could lead to exotic forms of superconducting order, such as a spin triplet state, which is compatible with ferromagnetic order. The interest in the interaction of magnetism and su­perconductivity is further heightened by the possibility that magnetic excitations may play a key role in the binding of Cooper pairs in exotic systems, playing an analagous role to that of phonons in conventional BCS theory. The ¿¿SR tech­nique has played an extremely significant role in the investi­gation of many systems where magnetism and superconduc­tivity exist.

Magnetic multilayers, with neighbouring magnetic and superconducting layers, afford the possibility to produce mo­del systems with which to probe the interaction of the two competing order parameters. While a significant amount of both theoretical and experimental work has been done on such systems, there are few suitable microscopic methods with which to study them. This is due to the small layer thicknesses which can be grown, which have a practical up­per limit of a few thousand Angstroms for good quality films. The Low-Energy ¿¿SR (LE-¿¿SR) technique is an obvious way to approach this problem, particularly in view of the great success with which it has been applied to looking at sur­face flux profiles in high-T c superconductors [1]. Here it was shown that, as expected in the London limit, the external flux near the surface is screened in an exponential way with depth into the superconductor.

In the last round we had effectively about 48 hours of us­able beamtime in which to perform prehminary experiments on a hybrid multilayer system of ferromagnetic iron and su­perconducting lead. This system was chosen to give very clean, flat interfaces, and the relative thicknesses chosen so that the iron is just starting to exert a measurable effect on the bulk superconducting properties. Above T c , when the lead is not superconducting, by implanting muons in the supercon­ductor close to the ferromagnetic interface, we observed the probability distribution p(B) of Fig. 1. The form of P(B) is highly reminiscent of that expected from an RKKY spin density wave due to the polarisation of the conduction elec­trons by the ordered moments in the iron layer. This signa­ture falls away as the muons penetrate further into the bulk of the non-magnetic metal, as would be expected if this were indeed the origin of the signal. A specific simulation of the

RKKY propagation in this system will have to be performed and compared to much higher statistics data in order to reach any stronger conclusion. Nonetheless, it is encouraging that when the sample is cooled to below the superconducting tran­sition there is a significant smearing of the features of p(B), although intriguing that some characteristics still persist. It is also noteworthy that below T c , with increasing muon pen­etration into the superconducting sample, the simple flux ex­pulsion expected from pure lead is not observed. This may not be unexpected if the influence of the magnetic layer ex­tends well into the superconducting bulk. It will be necessary to perform bulk magnetisation measurements on the particu­lar sample used in the LE-¿¿SR experiment, in order to make quantitative comparison. This was not done prior to the ex­periment in order to preserve the integrity of the sample. We note with interest that theories of the superconducting ground state in magnetic-superconducting multilayers have suggested a combined 'spin density wave' and superconduct­ing character inside the magnetic layers [2]. Here the ex­change field is periodically compensated by oscillations of the pair amplitude. In conclusion, we believe these LE-¿¿SR results, although highly preliminary, are sufficiently encour­aging to warrant further investigation.

0.015 0.02

Internal field B(T)

Figure 1: Probability distribution p(B) in Pb, close to the ferromagnetic interface, both above and below T c . A small downward shift in the average field can be seen below T c due to the expulsion of flux from the sample.

REFERENCES

[1] T. Jackson era/., Phys. Rev. Lett. 84,4958 (2000).

[2] M. G. Khusainov and Yu. N. Proshin et al, Phys. Rev. B 56, R14283 (1997).

66

SLOW MUON EXPERIMENTS ON A SUPERCONDUCTOR / FERROMAGNET Y B a 2 C u 3 0 7 / S r R u 0 3 SUPERLATTICE

Ch. Niedermayer1, C. Bernhard2, H. U. Habermeier2, F. Treubel1, G. Schatz1, N. Garifianov4, R. Khasanov4, H. Luetkens3'4, F. J. Littersfî, E. Morenzoni4, T. Prokscha4, A. Suter4

K O N S T A N Z 1 - M P I S T U T T G A R T 2 - B R A U N S C H W E I G 3 - P S I 4

It has previously been shown that the competition be­tween ferromagnetic (FM) and superconducting (SC) order in superlattices of YBa2Cu30 7 high-T c cuprate supercon­ductor and FM SrRu03 or L a ^ C a ^ M n O s involves a sur­prisingly large length scale of several hundred Angstroems far in excess of the SC coherence length [1]. Furthermore, the mutual interaction between SC and FM not only leads to a strong suppression of both phenomena but also gives rise to a metal/insulator transition that is rather unexpected since the individual layers are metals. Field cooled and zero field cooled DC SQUID magnetization measurements obtained at 5 Oe for the YBa 2 Cu 3 O 7 (400 Â) / SrRuO 3(200 Â) superlat-tice used in our study are displayed in Figure 1. The zero field curve shows a large diamagnetic shift below T c « 65 K, whereas the ferromagnetic transition at Tc u r ie ~ 120 K is more clearly seen in the field cooled curve.

Temperature [K]

Figure 1 : Temperature dependence of the magnetization in an external field of 5 Oe. The zero field curve (blue) shows a large diamagnetic shift below T c « 65 K, whereas the fer­romagnetic transition at Tc u r ie ~ 120 K is more clearly seen in the field cooled curve.

ergy of 8 keV where all muons are stopped within the first Y B a 2 C u s 0 7 layer.

For Tcurie = 120 K > T > T c = 65 K only a moderate de-polarisation rate is observed, which may arise from the stray fields due to the magnetic domain boundaries of the SrRuOs layers. Right below Tc, however, the depolarisation rate ex­hibits a strong and rather sudden increase. In fact, already at 30 K the depolarisation has become so rapid that less than 50 % of the asymmetry remains after the first 10 ns which are not accessible with our present setup. The increase of the depolarisation rate below T c signals a corresponding in­crease of the magnetic moments within the superconducting YBa 2 Cu307 layer. Certainly it cannot be explained due to the formation of a flux-line-lattice in the SC state. This re­sult agrees very well with the observed increase of the spon­taneous magnetisation in dc-magnetometry (see Fig. 2) and implies that the magnetic coupling via the YBa 2 Cu307 layer is strongly enhanced in the SC state. Presently we have no definite explanation for the observed effect which seems to contrast general wisdom that superconductivity tends to re­duce magnetic order.

0.1 T 0.5 T 5 T

Temperature (K) 20 40 60 80 100 120 140 160

Temperature (K)

Another remarkable observation concerns the tempera­ture dependence of the field-cooled magnetisation which ex­hibits a dramatic increase in the SC state (see Figure 2). In marked contrast to the naive expectation that the FM order parameter should be (at least) partially suppressed at the on­set of Superconductivity inside the YBa 2 Cu30 7 layers, the field-cooled magnetisation exhibits a very strong and rather sudden increase below T c .

In order to shed more light on this interesting phenomenon we have employed the technique of low-energy muon-spin-rotation (LEM) and investigated the distribution of local mag­netic fields inside an YBa 2 Cu30 7 layer. Figure 2 presents weak transverse field data (at 100 Oe) at an implantation en-

Figure 2: Left: Temperature dependence o f the magnetiza­t ion i n different external fields. The magnetisation shows a dramatic increase below the supercondcuting transition tem­perature. Right: LE-/iSR data obtained in a transverse field of 100 Oe after implanting the muons into the Y B a 2 C u 3 0 7

layer.

REFERENCES

[1] H. U. Habermeier, G. Christiani, R. K. Kremer, O. Lebedev, G. van-Tendeloo, Physica C 364-365,298 (2001).

67

HIGH FIELD ¿/SR-MEASUREMENTS IN THE MAGNETIC PHASE OF THE HEAVY

FERMION COMPOUND Ce r Ni 3

D. Andreica1, F. N. Gygax2, A. Schenck2, K. Uemo3 and T. Takabatake3

RA-01-07, CLUJ1 - ETH ZÜRICH 2 - HIROSHIMA3

Ce7NÍ3 possesses a complex antiferromagnetic phase be­low 1 .8 K. The three crystallographically inequivalent Ce-sites are associated with differently strong ordered moments of which one: Li(Ce3) ~ 0 . The AF order can be suppressed by a moderate pressure of 0 . 3 3 GPa. Non Fermi liquid (NFL) behavior appears instead around 0 . 4 GPa [ 1 ] . Two muon sites in Ce7NÍ3 were identified in earlier LI+ Knight shift measure­ments with a population ratio of 5 : 1 just above T J V [ 2 ] .

Recently it was discovered that the magnetic phase dia­gram of Ce7Ni 3 in the H-T plane at ambient pressure is also rather complex [ 3 ] . It appears that there is a field induced ferromagnetic phase above 0 . 6 T and below 0 . 6 K. The com­plicated antiferromagnetic phase in zero field seems to be destroyed above 0 . 3 T. Nothing is known about the structure of the intermediate phase. To learn more about this phase we have performed field dependent TF-//SR measurements at 2 0 0 mK and 4 0 0 mK, using the LTF. The field Hext was applied parallel to the c-axis and was varied between 0 . 0 5 T and 1 .5 T. Since one can rotate the LI+ -polarization by only about 45° from horizontal to vertical by the spin rotator there is a sizable LI+ -polarization component parallel to the ap­plied field and a LF-signal can be observed in the forward and backward detectors which followed a simple exponen­tial decay.

In the TF-signal below 0 . 1 5 T only a heavily damped sin­gle frequency component was visible, while above 0 . 1 5 T two frequencies 1/1,1/2 appeared (see Fig. 1 ) with an ampli­tude ratio of ~ 5 : 1 , suggesting that the two frequencies are associated with the two identified muon sites. Above 0 . 3 5 T vi and 1/2 rise linearly with Hext, which implies that Hext

and the internal fields are collinear. Since no further split­ting is seen, the internal fields at each site must arise from a ferromagnetic state.

Most interesting is the spin-lattice relaxation behavior of the muon polarization component along Hext. The spin-lattice relaxation rates are shown in Fig. 2 . Both at 2 0 0 mK and 4 0 0 mK a sharp change happens at 0 . 2 T which seems to indicate some sort of phase transition. This field value is also the critical field above which the splitting of the precession signal into two components develops, indicating the onset of a ferromagnetic component. Pure ferromagnetism is estab­lished at Hext ~ 0 . 3 5 T.

From the point of view of the //SR-measurements the phase diagram shows also a transition at 0 . 2 T for temper­atures between at least 2 0 0 mK and 4 0 0 mK. The onset of ferromagnetism is clearly evident in our data but appears to happen already for Hext ~ 0 . 3 5 T in contrast to other find­ings [ 3 ] . However, we do not see any suppression of mag-

Field (T)

Figure 1: Field dependence of 1/1 and 1/2 at 2 0 0 mK (a) full range, (b) blow up of (a). The solid line represents I/Q =

¿' 1 1 1

A

1 1 1 1 1 1 1 1 1 1 1 û 200 mK ¿' 1 1 1

A 0 400 mK

_ 0 a

-0 •

1 1 1 1 1 1 1

A" &ÔQOÔO0OOOO ~

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 Field (T)

Figure 2 : Field dependence of LF-relaxation rate at 2 0 0 mK and 4 0 0 mK. Note the change at 0 . 2 T.

netic order. Also for Hext > 0 . 3 5 T no anomalies show up in our data up to 1 .5 T.

REFERENCES

[ 1 ] K. Umeo, H. Kadomatsu, T. Takabatake, Phys. Rev. B 5 4 , 1 1 9 4 ( 1 9 9 6 ) .

[ 2 ] A. Schenck, D. Andreica, F. N. Gygax, K. Umeo, T. Takabatake, E. Schreier, A. Kratzer, G. M. Kalvius, J. Phys.: Condens. Matter 1 3 , 4 2 7 7 ( 2 0 0 1 ) .

[ 3 ] K. Umeo, private communication.

68

THE MAGNETIC GROUNDSTATE OF THE KONDO ALLOYS C e N i i ^ C u * BY ¿xSR

N. Marcano1, J. C. Gomez-Sal1, G. M. Kalvius1, D. R. Nookes3, R. Wäppling4, Ch. Baines5

RA-01-08, CANTABRIA1 - TU MÜNCHEN 2 - VIRGINIA STATE3 - UPPSALA 4 - PSI 5

The pseudo-binary system CeNii-^Cu^ is a fine exam­ple to study the competition between Kondo and RKKY in­teractions in the presence of atomic disorder. CeNi stabilizes in the orfhorhombic CrB-type structure (Cmcm) and CeCu in the FeB-type structure (Pnmo). The pseudo-binaries main­tain the FeB-type structure for a; > 0.15. Bulk studies have established a complex magnetic phase diagram where a spin-glass-like precursor state is observed before long range mag­netic order (LRO) sets in [1]. CeCu is a simple antiferro­magnet (AFM) with the moments in the ac plane. CeNi is non magnetic (Pauli paramagnet). Neutron scattering [2] has shown that for x = 0.6 the ground state is ferromag­netic (FM) with b being the easy axis. For 0.9> x >0.6 the magnetic ground state shows complex spin order (e.g. for x = 0.9 an overlay of two spin lattices, one resembling the AFM structure of CeCu, the other a FM structure with mo­ments in the b direction). LRO has been established down to x = 0.4. It certainly vanishes around x = 0.1, but the question was open for x = 0.2 at the onset of this study. Here, we re­port ZF-//SR spectroscopy on polycrystalline samples with x = 0.9,0.6,0.5,0.2 carried out at the LTF facility.

0.25-

0.00-1 . . . 1 0.0 0.5 1.0 1.5 2.0

Time (us"1)

Figure 1: ZF spectra at 0.04K for some CeNii-^Cuj; alloys.

In all alloys studied a LRO state is present at base tem­perature (0.04 K). The pSR response for an LRO magnet is A(t) = A 0 [ | e x p ( - A T i ) c o s ( 2 7 r ^ M i ) + | e x p ( - A L i ) ] . A T and A¿ are the transverse and longitudinal muon spin re­laxation rates, the former being mainly sensitive to the static width of the local field distribution, the latter only to spin-dynamical processes. Fig. 1 shows the ZF-//SR spectra at

0.4 K and Table I gives the fit parameters. Spontaneous spin precession is only seen in the x = 0.9 sample. In all others the transverse signal relaxes monotonically, i.e. XT > uiß = 2TÏVi1 = jßB^. The internal fields listed in Table I have been estimated from spectral simulations.

Table I: pSR spectral parameters at 0.04 K. Compound A 0

Bß(G) A T A L x2

CeNio.iCuo.9 0.26 1200 45 0.09 1.2 CeNi 0.4Cu 0.6 0.27 ~500 45 0.31 1.2 CeNio. 5Cu 0.5 0.23 ~700 80 0.12 1.1 CeNio. 8Cu 0.2 0.24 ~ 7 0 9.1 0.09 1.3

To obtain information on the muon stopping site, we per­formed crystal field potential calculations assuming that the muon selects the largest and 'deepest' interstitial hole (see Fig. 2). Its unit cell coordinates are (0.346,1/4,0.538). Dipole field calculations based on the FM spin structure of [2] gave Bß ~0.95kG per P B - Using porci=0.6 PB from [2] we ob­tain Bß ~ 5 6 0 G in acceptable agreement with the pSR re­sults. B„ ~ 7 0 G for £ = 0.2 then gives U^h ~0.075/xs.

0 .

Figure 2: Muon site (dark dots) in CeNii-^Cuj;.

In summary, all spectra are fully compatible with mag­netic LRO, but local spin disorder must be substantial. The decrease of A T for x = 0.2 reflects the reduction in Ce or­dered moment. In general, the ratio Xr/Bß remains about constant. The disorder in spin structure is little affected by the Ni content. A¿ does not reach zero in most cases at base temperature, indicating the presence of persistent spin fluctu­ations. Those have been observed in other disordered Kondo systems. The large transverse relaxation rate is not compati­ble with a simple FM structure for x = 0.6, especially in view of the fact that the x = 0.9 material with its fairly complex non-linear AFM structure still exhibits resolved spontaneous spin precession. For x = 0.5 FM properties are safely estab­lished by magnetization data, yet the same argument against a simple FM structure applies on the basis of the pSR data. A revision of spin structure data is called for.

REFERENCES

[1] J. GarciaSoldevillaetat, Phys. Rev. B 61,6821 (2000).

[2] J. I. Espeso et ai, Eur. Phys. J. B 18, 625 (2000).

69

FIELD INDUCED MAGNETIZATION DISTRIBUTION AND ANTIFERROQUADRUPOLLAR

ORDER IN C e B 6

A. Schenck1, F. N. Gygax1, S. Kunii2

RA-98-16, ETH-ZÜRICH1 - SENDAI 2

Since the early 80-ties the cubic, dense Kondo compound CeB6 has been the subject of intense and continuing studies due to the puzzles raised by its rich phase diagram which consists of a low temperature antiferromagnetic phase below TV = 2.25 K (phase III), an antiferroquadrupolar phase be­low TQ = 3.3 K (phase II) and a paramagnetic phase above TQ (phase I). In phase II it is claimed that an antiferromag­netic order can be induced by an external field. Recent polar­ized neutron scattering has provided evidence that in phase II and phase I moments are not only induced at the Ce-sites, but also near the B6-molecule [1]. To study in particular phase II in more detail we have performed Knight shift measure­ments at 0.6 T on a newly prepared high quality single crys­tal. We find two components in the TF-signal with ampli­tude ratio 2:1 and an anisotropy ratio of the Knight shifts of 1:2 in the full temperature range covered (2.3 K - 200 K). These features imply that the l i + occupy the interstitial d-sites ( (00 | ) and equivalent). The temperature dependence of the observed precession frequencies for i î e x i | | [ 100 ] and II [110] is displayed in Fig. 1. We notice an abrupt change at TQ, a coincidence of all frequencies independent of the sam­ple orientation at ~ 2.5 K and a reversal of the anisotropy sign below 2.5 K. Above 10 K we find that the extracted Knight shifts scale linearly with the magnetic bulk suscep­tibility. From the slopes we determine a dipolar coupling constant of AZZ = 5.94 kG / /Xß. This is much larger than the value of 3.95 kG//xß calculated for the (/-site. Since the d-site assignment is the only possible one, we are forced to consider the possibility of additional sources for dipole fields. It turns out that negative magnetization placed at the boron sites or the b-, c- or g-sublattice sites are qualitatively in agreement with [1] and also with theoretical predicitons [3]. The abrupt changes at TQ then imply that these additional magnetization densities are strongly affected by the onset of the antiferro­quadrupolar order. Below TQ they start to decrease, change to a positive sign somewhere below TQ, and bring about a cancelation of the total dipolar fields at the /x + at ~ 2.5 K. Following [2] we attribute this behavior to the hybridization of the 4 / and the boron 2s- and 2p-electrons which depends on the relative orientation of the nonspherical 4/-charge dis­tribution with respect to the 2s- and 2p-charge distributions.

The absence of any further splitting of the /xSR-signal below TQ (in contrast to NMR-results [3]) implies that the claimed field induced antiferromagnetic state must be of the simple G-type.

N I

Ü C <D

CT

[100]

[110]

[110] , ^ .

[100] J_LJ_

A , o Signal I • , 0 Signal II

10 1

Temperature (K) 10 2

Figure 1: Temperature dependence of the precession fre­quencies of the two observed components for Hext 11 [001] and Hext 11 [110]. The insert shows a blow up of the low tempera­ture part which demonstrates that all frequencies collaps to a single value at 2.5 K.

REFERENCES

[1] M. Saitoh et ai, proceedings of ORBITAL 2001, to be published in J. Phys. Soc. Jpn.

[2] K. Hanzawa, J. Phys. Soc. Jpn 70,1900 (2000).

[3] M. Kawakami et al, J. Phys. Soc. Jpn 50,432 (1981).

70

STUDY OF THE MAGNETIC PROPERTIES OF C e 3 P d 2 0 S i 6 AND C e 3 P d 2 0 G e 6 COMPOUNDS

V. N. Duginov1, A. V. Gribanov2, K. I. Gritsaj1, A. A. Nezhivoy3, V. N. Nikiforov2, V. Yu. Pomjakushin1, A. N. Ponomarev3, Yu. D. Seropegiri2

RA-97-04, DUBNA 1 - MOSCOW 2 - KURCHATOV3

Magnetic properties of Ce3Pd2oSi6 and Ce3Pd2oGe 6

are very unusual. A pronounce anomaly in the molar mag­netic moment near 60 K and 'superparamagnetic' depen­dence of magnetic moment versus applied field for this com­pound allows to suppose the existence of magnetic transi­tion near this temperature. To explain such unusual behavior of Ce3Pd2oSÍ6 a model of 'molecular' magnetism was sug­gested for one of two cerium sublattices. In Ce3Pd2oGe6 molar magnetic moment obeys Curie-Weiss law down 4.2 K, but the difference A M between Mpc and M z f c begins to develop below 65 K.

After our previous experiments we mentioned that all magnetic anomalies can be observed only at sufficient low magnetic field. In the experiments on the GPD setup we con­centrated our efforts on the detailed study of the magnetic properties of Ce3Pd2oSÍ6 at low magnetic fields. We have performed the TF experiments in the field range 50 - 400 G at the temperatures below 50 K. The temperature dependence of the magnetic field seen by the muons at i î e x t = 300 Oe is shown in Fig. 1.

Ce3Pd20S¡6

4.0770 r

4.0765 -

4.0760 -N

I

4.0755 ->. Ü <D

cr 4.0750 -2Í

4.0745 -

4.0740 -

4.0735 -

Ce3Pd20Si6

- i 1

ï f

10 20 30 Temperature, K

50

Figure 1: The temperature dependence of the muon spin pre­cession frequensy in i f e x t = 300 Oe.

One more result obtained at these experiments is pre­sented on Fig. 2. One can see that there is no difference between FC and ZFC results above 15 K, but the decrease of the temperature leads to the splitting of the FC and ZFC curves. Similar behavior was observed in the macroscopic magnetization measurements of M(T) below 5 K in i f e x t = 10 Oe. We hope to continue the experiments in this direction at the temperatures below 10 K.

The results of the other experiments at low magnetic field need more analysis.

We continued the search of the AF ordering in the Ce3Pd2oGe6 compound below 1 K. Zero-field pSR mea­surements were performed on the LTF setup. The temper-

30 40 50 Temperature, K

Figure 2: The temperature dependence of the muon spin de­polarization rate at the FC and ZFC procedures in i f e x t = 200 Oe.

ature dependence of the muon spin depolarization rate is shown in Fig. 3. The distinct increase of the muon spin depo­larization rate is observed at the temperature of the supposed transition, but the clear muon spin precession signal was not obtained.

Ce3Pd20Ge6

0.25

0.20 N

X

5 S 0.15 c o

I 0.10

oc 0.05

ï ï

0.00 1 1 1 1 1 1 1 1 1 1

0.5 0.55 0.6 0.65 0.7 0.75 0.8 0.85 0.9 0.95 1 Temperature, K

Figure 3: The temperature dependence of the muon spin depolarization rate near the expected AF transition in Ce3Pd2oGe6 at ZF measurements.

The experimental spectra are described quite well by the one component polarization function at the temperatures above 0.5 K. But below this temperature the depolarization function has got the more complicated form.

71

¿/SR MAGNETIC STUDIES OF E r B 1 2

G. M. Kalvius1, D. R. Nockes2, R. Wäppling3, F. Iget*, T. Tahabatahe4,

RA-01-10, TU MÜNCHEN 1 - VIRGINIA STATE2 - UPPSALA 3 - HIROSHIMA4

The crystal structure of RB12 compounds is most easily visualized as a rock salt (NaCI) structure with the rare earth (R) atoms on the Na site and B12 cubo-octahedral clusters centered on the CI site. Bulk magnetic data [1] show an anti­ferromagnetic (AFM) transition at 6.7 K. No information on the ordered spin structure exist. The Curie-Weiss moment is 9.5 P B , i-e. close to the free ion value and for the param­agnetic Curie temperature @ p = —14.6 K is reported. The pSR measurements were carried out at the GPS facility with a sample consisting of a mosaic of non-oriented single crys­tal platelets glued to a Ag backing. ZF-pSR spectra confirm a magnetic transition at 6.5 K. No spontaneous spin preces­sion is visible below Tn (Fig. 1, left). The spectral shape is always dominated by the large transverse (static) relaxation rate At- Thus At and the (dynamic) longitudinal relaxation rate A¿ are the only magnetic parameter to be extracted in the ordered state. There is little change of those two parameters between 4.2 K and 6.4 K ( A T « 45 ps'1, XL « 0.2 ps~v).

0.0 0.2 0.4 0.6 0 2 4 6 8 Time (us)

Figure 1 : ZF spectra in the magnetic and transition regimes.

6 7 8 9 10 11

Temperature (K)

Figure 2: The magnetically ordered fraction.

Between 6.7 K and 9 K one observes a mixture of mag­netically ordered and paramagnetic fractions. An example shows the spectrum at 6.7 K in Fig. 1. At 10.4 K the full para­magnetic response (simple exponential relaxation) is present. The temperature dependence of the magnetic volume frac­tion is plotted in Fig. 2. This behavior together with the fact that the magnetic parameters change little on approach (from below) to T n strongly suggests first order character of the magnetic transition. From spectral simulations we estimate the local field to be on the order of 500 G. This is a low value for the large moment (roughly 1 0 P B ) of Er. Partial field compensation is likely in accordance with AFM order. The condition for relaxation dominance in the transverse part of

the spectrum in an ordered state is At > JßBß emphasiz­ing that the mean local field and its distribution width are approximately of the same magnitude. This indicates sig­nificant spin disorder (probably spin-directional) on a short range scale (< 5 lattice constants), a curious result in view of the fact that we deal with a stoichiometric compound where the magnetic ion (Er) is located on a well defined lattice site.

50K 5K

100K 30K

100K

200K 150K

2 0 0 K V < S ' ^ S * ^ - S i

0 2 4 6 8 0 2 4 6 8

Time ( u s 1 )

Figure 3: ZF spectra of ErBi 2 and YbBi 2 .

The spectra above Tn are fully dominated by electronic (magnetic) relaxation up to 100 K. The strong 1 1 B nuclear relaxation needs to be included only at higher temperatures. Yet, even at 250 K the magnetic relaxation influences signifi­cantly the spectral shape. Spin-spin correlations must be very strong. Typical ZF spectra are shown in Fig. 3 together with data for non magnetic YbBi 2 . The fits shown for ErBi 2 are double (nuclear+electronic) relaxation functions. The fits for YbBi 2 are two nuclear Kubo-Toyabe (KT) patterns (with dif­ferent static widths) of varying relative intensities (see [2]). Above ~ 1 5 0 K only one KT function is present. Such de­tails cannot be extracted from the spectra of ErBi 2 , but their analysis reveals that a nuclear KT function of constant static width (A) will not work. A change of A is needed around 150K. This temperature correlates in the two R B i 2 com­pounds. In YbBi 2 we had suggested motional effects within the B i 2 clusters as the relaxation mechanism [2]. Both, spin and molecular motions are present in ErBi 2 , but more studies are needed to clarify their relations.

REFERENCES

[1] S. Gabáni et al., Acta Phys. Slovaca 48 ,7 5 5 (1998).

[2] G. M. Kalvius et al., Physica B , in press.

72

SLOW SPIN DYNAMICS IN NON-FERMI-LIQUID UCus^Pd* , x = 1.0 AND 1.5

D. E. MacLaughlin1, R. H. Heffner2, O. O. Bernai3, G. J. Nieuwenhuys4, J. E. Sonier2, M. S. Rose1, R. Chauh, M. B. Maple5, B. Andraka6

RA-00-15, RIVERSIDE1 - LANL 2 - LOS ANGELES 3 - LEIDEN 4 - SAN DIEGO 5 - GAINESVILLE6

We have carried out muon spin-lattice relaxation mea­surements in the non-Fermi-liquid (NFL) alloys UCus-^Pd^, x = 1.0 and 1.5 (see also Ref. [1]). A characteristic time-field scaling of the muon asymmetry relaxation function G(t,H) = Git/H1) is observed, which shows that these systems ex­hibit long-lived spin correlations reminiscent of quantum crit­ical dynamics [2] or of disordered materials such as spin glasses [3].

Asymmetry functions G{t) forUCus.sPdi.s andUCu4Pd are given in Figs. 1 and 2, respectively, for temperatures of 0.05 K and 0.5 K. The data are plotted as functions of the

20

10 -

e o

i—i—i i i 11 j 1 1—i—i i i 11 j 1 1—i—i i i 11 j

U C U 3 . 5 P d 1 . 5 (a) 7 = 0 . 0 5 K

• H = 1 3 0 e

• 28 Oe A 100 Oe

250 Oe • 630 Oe O 1 0 0 0 O e

0.01 0.1

20 -

10 -

1 1 1 1 1 1 1 —i—i—i i i i j 1 1 1—i—i i i i j . • „ ( b ) T = 0 . 5 K -

A H = 35 0 e 0 100 Oe T 250 Oe • 1 0 0 0 O e + 2500 Oe

• 1 , , I •

0.01 0.1

Figure 1: Dependence of sample-average muon asymme­try relaxation function G(t) on scaling variable t/H1 in UCu 3 . 5 Pdi. 5 . (a)T 7 = 0.5 ± 0 . 1 .

0.05 K, 7 = 0.7 ± 0 . 1 . (b)T = 0.5 K,

scaling variable t/H7, where 7 is varied to obtain the best scaling, i.e., the most nearly universal behavior. The time-field scaling indicates that the local spin dynamics are char­acterized by a power-law dynamic susceptibility

x"(r,u>)/u> oc uj~ (1)

at low frequencies. It is important to note that no particular form for G(t) is assumed in this analysis.

In UCu3. 5Pdi.5 7 from muon relaxation exhibits a tem­perature dependence, becoming larger at low temperatures: 7(0.5 K) = 0.5 ± 0.1; 7(0.05 K) = 0.7 ± 0.1. This is rem­iniscent of the behavior of spin-glass AgMn above the spin-freezing "glass" temperature T9, where 7 increases as T —>

20 -

10 -

£ 0 I 20 CO

10

UCu 4Pd ' " H D » ( a ) T = 0 . 0 5 K

H=15 0 e 45 Oe 100 Oe 200 Oe 500 Oe 1 0 0 0 O e

(b) 7 = 0 .5K

_ • H = 21 Oe

• 68 Oe A 250 Oe

- 630 Oe

- • 1600 Oe

0.001 0.01 0.1

Figure 2: Dependence of G(t) on f / Í P in UCu 4Pd. (a) T = 0.05 K. (b) T = 0.5 K. At both temperatures 7 = 0.35 ± 0.10.

Tg [3]. It suggests a continuous temperature dependence of 7 in UCu3.5Pdi.5 between the low-temperature muon relax­ation results and the higher-temperature (> 10 K) inelastic neutron scattering (INS) value 7 = 0.33 [2].

In UCu 4Pd, on the other hand, 7 = 0.35 ± 0.10 from muon relaxation at both 0.05 K and 0.5 K (Fig. 2). This value is smaller than in UCu3.sPdi.5, and in agreement with INS experiments above 10 K [2] which give 7 = 0.33 as in UCu3.5Pdi.5. This temperature independence suggests that in UCu4Pd the slow fluctuations are quantum rather than thermal in origin. In UCu3.sPdi.5 the Pd concentration x is closer to the value x « 2 for which a spin-glass phase oc­curs [4], and the proximity of this phase may be reflected in the low-temperature increase of 7 .

Time-field scaling and other aspects of these experiments are discussed in detail elsewhere [1].

REFERENCES

[1] D. E. MacLaughlin et al, Phys. Rev. Lett. 87,066402 (2001); PSI Sei. Rept. 2000,1,60 (2001).

[2] M. C. Aronson et al, Phys. Rev. Lett. 75,725 (1995).

[3] A. Keren et al, Phys. Rev. Lett. 77,1386 (1996).

[4] B. Andraka and G. R. Stewart, Phys. Rev. B 47, 3208 (1993).

73

SPIN DYNAMICS IN SUBSTITUTED MANGANATES

S. J. Blundell1, C. A. Steer1, A. I. Coldea1, F. L. Pratt2,1. M. Marshall1 andJ. F. Mitchell3

RA-97-19, OXFORD 1 - ISIS 2 - ARGONNE 3

Stacks of n pervoskite layers, separated by layers with the rock-salt structure, form the basis of Ruddlesden-Popper (RP) phases. There has been recent significant interest in colossal magnetoresistance (CMR) in both perovskites (n = oo) and layered perovskites (n = 2) based upon Mn. We have used /xSR at PSI to perform detailed measurements of the internal magnetic order in the n = 2 RP manganites La2-2zSri + 2zMn 207 as a function of doping [1,2] This sys­tem possesses an extremely rich phase diagram [3]. Raw muon data are shown in Figure 1 for a range of doping levels.

0.0 0.1 0.2 t (lis)

Figure 1: /xSR data at 1.8 K for La2-2zSri + 2zMn 207. The ground states for the 5 phases are believed to be as follows: ferromagnetic with spins in the plane for x = 0.4, A-type an­tiferromagnetic for x = 0.52, glassy for x = 0.68, C/C* an­tiferromagnetic for a; = 0.82 and G-type antiferromagnetic for x = 0.98.

These systems show greatly differing low temperature ground states as a function of doping, as seen in the greatly different /xSR data. In the x = 0.98, two clear precession signals are visible whose temperature dependence is shown in Figure 2(b). The temperature dependence of the sample

with x = 0.52 is shown in Figure 2(a), which shows an anomaly close to 100 K which may be connected with the competition between two coexisting phases. The x = 0.68 data are also of special interest since no neutron Bragg peaks were observed for this sample. We find that spin freezing occurs as the sample is cooled below a freezing temperature which is about 70 K. These results will be presented in detail elsewhere [1].

T (K) T (K)

Figure 2: Temperature dependence of the internal field for two of the samples shown in Figure 1.

Other /xSR work which we have performed this year (at PSI and ISIS) on magnetic oxides has included magnetoresis-tive sulphides [4], Rh [5] and Ga [6] doped perovskite man­ganites, and frustrated oxides [7].

REFERENCES

[1] A. I. Coldea, C. A. Steer, S. J. Blundell, F. L. Pratt, J. F. Mitchell, in preparation.

[2] A. I. Coldea, Thesis, University of Oxford (2001).

[3] C. D. Ling, J. E. Millburn, J. F. Mitchell, D. N. Argyriou, J. Linton and H. N. Bordallo, Phys. Rev. B 62,15096 (2000).

[4] P. Vaquerio, A. V. Powell, A. I. Coldea, C. A. Steer, I. M. Marshall, S. J. Blundell, J. Singleton and T. Ohtani, Phys. Rev. B 64,132402 (2001).

[5] A. I. Coldea, L. D. Noailles, I. M. Marshall, S. J. Blundell, J. Singleton, P. D. Battle and M. J. Rosseinsky, Phys. Rev. B 62, R6077 (2000).

[6] A. I. Coldea, S. J. Blundell, I. M. Marshall, C. A. Steer, F. L. Pratt, P. D. Battle,L. D. Noaillles and M. J. Rosseinsky, Phys. Rev. B 65,054402 (2002).

[7] I. M. Marshall, S. J. Blundell, F. L. Pratt, A. Husmann, C. A. Steer and W. Hayes, submitted to J. Phys.: Condens. Matter.

74

/x+SR ON FERROELECTROMAGNETIC PEROVSKITES

G. J. Nieuwenhuys1, D. G. Tomuta1, J. Aarts1, J. A. Mydosh1, R. H. Heffner2, D. E. MacLaughlin3

RA-00-07, LEIDEN 1 - LANL 2 - RIVERSIDE3

The REMn03 with RE = Ho, Er, Tm Yb and Lu, Y M n 0 3

and ScMn) 3 crystallize in a hexagonal structure with space group P6 3cm. The other rare-earth manganites attain an or-thorhombic crystal structure (Pnma) and form the now well known class of colossal magnetoresistance materials. The latter have been studied extensively also with the /xSR tech­nique [1].

The hexagonal compounds belong to another interesting class: the ferroelectric materials. They all show ferroelectric-ity at temperatures below about 500 K [2], so for the present purpose they are in a ferroelectric state, which is among oth­ers reflected in the crystal structure in such a way that there is no mirror symmetry with respect to a mirror parallel to the basal plane [3].

At lower temperatures (around 80 K) all the hexagonal compounds order antiferromagnetically. In this antiferro­magnetic state the Mn spins are in the basal plane, making angles of 120° with respect to each other. There are 4 possi­ble arrangements of these spins: P 6 3 c ' m \ P 6 3 ' c m \ P6 3 'c'm and P6 3 cm [4]. The first two magnetic group describe the neutron diffraction results of Lu-, Yb-, Tm- and ErMn0 3 , and Sc- and HoMn0 3 above 50 K, while the last two groups describe Y M n 0 3 and the low temperature phases of Sc- and HoMn0 3 . Neutron diffraction cannot distinguish between e.g. P 6 3 V m and P6 3cm.

As is also evident from our neutron diffraction results [5] the rare earth moments are being aligned due to exchange interaction with the ordered Mn ions [6, 7]. For Tm- and YbMn0 3 this leads to strong diffraction lines, for Ho- and ErMn0 3 these lines are much weaker.

Figure 1 : The spontaneous precession frequency as a func­tion of reduced temperature for LuMn0 3 and ScMn0 3

The aim of the present work is to collect information on the internal magnetic fields, which will help to deduce the magnetic structure in more detail. We have carried out zero-field experiments on all compounds and in particular on Y-, Tm- and YbMn0 3 also on single crystals.

,w v v v

o o 0

o o o o Er V Ho

O o

— I ' 1 ' 1 ' 1 ' 1 ' 1 —

0.0 0.2 0.4 0.6 0.8 1.0 T/TN

Figure 2: The spontaneous precession frequency as a func­tion of reduced temperature for ErMn0 3 and HoMn0 3

Our results can be summarized as follows:

• All compounds show spontaneous precession below T n (see Figs 1 and 2).

• For the lowest temperature in Yb- and TmMn0 3 , the frequency distribution of this precession becomes very broad.

• The frequency decreases in Ho- and ErMn0 3 , but re­mains sharp.

• The transition from one to the other magnetic sym­metry in Ho- and ScMn0 3 is not reflected in the fre­quency of the precession as a function of temperature.

• The internal magnetic field is directed along the crys­tallographic c-axis.

The symmetry of the internal field implies that the im­planted muon occupies a 2a or 4b site since these sites posses a three fold rotation symmetry around the vertical axis. An experiment on a single crystal of TmMn0 3 showed that the Knight shift at 100 K is +2.4 % for the field along the c-axis, which leads to a distance of 1.8 Â between the muon and the rare-earth ion. Calculations of the internal dipole field due to the Mn ordering show that this site can be in agreement with the observed frequencies.

REFERENCES

[1] R. H. Heffner et al, Phys. Rev. B 63,094408 (2001).

[2] G. A. Smolenskii and I. E. Chupis, Sov. Phys. Usp. 25,475 (1982).

[3] E. F. Bertaut and M. Mercier, Phys. Lett. 5,27 (1963); 18,13 (1965).

[4] D. Fröhlich et al, J. Appl. Phys. 85, 4762 (1999).

[5] D. G. Tomuta et al, to be published.

[6] K. Kritayakirana et al, Optics Comm. 1, 95 (1969).

[7] M. Fiebig et al, Phys. Rev. Lett. 88, (2002).

75

¿xSR STUDY ON COBALTITES OF TYPE R B a C o 2 0 5

U. Staub1, A. Amato1, E. Suard2, F. Fauth3, D. Herlach1, V. Caignaert4

RA-01-13, P S I 1 - I L L 2 - E S R F 3 - C P J S M Ä M S M R A C A E N 4

P e r o v s k i t e t y p e m a t e r i a l s a r e f o u n d to h a v e a s e r i e s o f

i n t e r e s t i n g m a g n e t i c a n d e l e c t r o n i c p r o p e r t i e s s u c h as h i g h -

Tc s u p e r c o n d u c t i v i t y , c o l o s s a l m a g n e t o r e s i s t a n c e (CMR) o r

m e t a l - i n s u l a t o r t r a n s i t i o n ( M I ) w i t h c h a r g e , o r b i t a l , and/o r

m a g n e t i c o r d e r i n g . H o B a C o 2 0 5 b e l o n g s t o th i s c l a s s o f m a ­

t e r i a l s a n d e x h i b i t s t w o d i f f e r e n t p h a s e t r a n s i t i o n s a t 340 K

a n d 210 K. A b o v e 340 K, t h e m a t e r i a l i s i n a p a r a m a g n e t i c

i n s u l a t i n g s ta te w i t h s o m e d e g r e e o f h o p p i n g . B e t w e e n 340 K

a n d 210 K, t h e m a t e r i a l i s a n t i f e r r o m a g n e t i c , w i t h a t u r n o v e r

i n r e s i s t i v i t y t o a m o r e i n s u l a t i n g s ta te . A t T o o = 210 K, a

c h a r g e o r d e r t r a n s i t i o n o c c u r s l e a d i n g to a d i s c o n t i n u i t y i n

t h e t e m p e r a t u r e d e p e n d e n c e o f t h e r e s i s t i v i t y . B e l o w T o o

t h e r e s i s t i v i t y c a n b e d e s c r i b e d b y a v a r i a b l e r a n g e h o p p i n g

m o d e l . T h e r e f o r e , T c o is a n a l o g u e to a M I t r a n s i t i o n . T h e

i n t e r e s t i n t h i s m a t e r i a l i s d u e t o i t s r e l a t i v e l y l a r g e CMR e f ­

f e c t f o r C o o x i d e s a n d t h e f a c t t h a t T N > T o o - U s u a l l y ,

T N < T C O ( T M I ) l i k e i n t h e R N Í O 3 m a t e r i a l s , w h e r e f o r

NdNiC-3 t h e m a g n e t i c t r a n s i t i o n i s i n d u c e d a t t h e T M I .

H e r e w e h a v e s t u d i e d t h e m a g n e t i c p r o p e r t i e s w i t h z e r o

field /xSR s p e c t r o s c o p y . F o r T o o < T < T N a s i n g l e f r e ­

q u e n c y i s o b s e r v e d w i t h a p p r o x i m a t e l y h a l f o f t h e e x p e c t e d

a s y m m e t r y f o r a p o l y c r y s t a l l i n e m a t e r i a l . B e l o w T o o a s e c ­

o n d f r e q u e n c y o c c u r s , i n d i c a t i n g tha t a t t h e s e c o n d m u o n

s t o p p i n g s i te t h e r e i s a s i g n i f i c a n t m a g n e t i c field f o r T <

T o o - F i g - 1 s h o w s t h e t e m p e r a t u r e d e p e n d e n c e o f t h e o b ­

s e r v e d f r e q u e n c i e s a n d t h e c o r r e s p o n d i n g r e l a x a t i o n r a t e s .

T h e s i g n i f i c a n t c h a n g e s o f t h e l o c a l field f o r m c l o s e t o z e r o

f o r T > T c o to a p p r o x i m a t e l y 20 M H z c a n b e e x p l a i n e d b y

t h e o c c u r r e n c e o f c h a r g e o rde r . F o r T > T c o a l l t h e C o i o n s

a r e i n t h e s a m e i n t e r m e d i a t e v a l e n c e s ta te o f C o 2 5 + , w h e r e a s

f o r T < T c o t h e C o i o n s t r a n s f o r m i n t o a n o r d e r e d a r r a y o f

C o 2 + a n d C o 3 + i o n s , f o r w h i c h t h e m a g n e t i c s a t u r a t i o n m o ­

m e n t s a r e 2.9 a n d 3.7 ps, r e s p e c t i v e l y [1]. T h i s s h o w s tha t

t h i s m u o n s t o p p i n g s i te i s l i k e l y a t a h i g h e r s y m m e t r y p o s i ­

t i o n a n d tha t t h e i r d i f f e r e n c e i s d i r e c t l y r e l a t e d to t h e d i f f e r ­

e n c e o f t h e t w o d i s t i n c t m a g n e t i c m o m e n t s . T h e m u o n r e l a x ­

a t i o n r a t e c o r r e s p o n d s d i r e c t l y t o t h e m a g n e t i c fluctuations o f

t h e a d d i t i o n a l m a g n e t i c m o m e n t o r d e r i n g a t T c o - T h e o t h e r

m u o n s t o p p i n g s i te c o r r e s p o n d s to a p o s i t i o n , w h e r e t h e i n d i ­

v i d u a l m a g n e t i c fields o f t h e C o i o n s a p p r o x i m a t e l y a d d a n d

a r e s e n s i t i v e t o t h e o r d e r p a r a m e t e r o f t h e s u m o f t h e m a g ­

n e t i c fluctuations o f t h e t o t a l m a g n e t i c m o m e n t s .

140

120

N I 100

w 80

O

S 6 0

D CT 2 40

20

0

I i i i i I i i i i I i i i i I i i i i I i i i i I

f l

f 2

T C O

0 50 100 150 200 250 300 350 T ( K )

Figure 1 : pSR frequencies and relaxation rates observed in H o B a C o 2 C > 5 in zero magnetic fields.

REFERENCES

[1] E. Suard, F. Fauth, V. Caignaert, I. Mirebeau and G. Baldinozzi, Phys. Rev. B 61, R11871 (2000).

76

SPIN FLUCTUATIONS IN GEOMETRICALLY FRUSTRATED RARE EARTH OXIDES

J. A. Hodges1, P. Dalmas de Réotier2, A. Yaouanc2, P. C. M. Gubbens3, S. Sakarya3

RA-01-15, C E A S A C L A Y 1 - CEA G R E N O B L E 2 - D E L F T 3

G e o m e t r i c a l l y d e r i v e d m a g n e t i c f r u s t r a t i o n a r i s e s w h e n t h e s p a t i a l a r r a n g e m e n t o f t h e s p i n s i s s u c h tha t i t p r e v e n t s t h e s i m u l t a n e o u s m i n i m i s a t i o n o f a l l i n t e r a c t i o n e n e r g i e s . I n t h e p y r o c h l o r e s t r u c tu r e c o m p o u n d s R 2 X 2 O 7 , t h e r a r e e a r t h i o n s (R) f o r m a sub- la t t i ce o f c o r n e r s h a r i n g t e t r a h e d r a a n d f o r a n u m b e r o f t h e r a r e e a r t h s , t h e s e c o m p o u n d s h a v e b e e n o b s e r v e d to e x h i b i t f r u s t r a t i o n - r e l a t e d b e h a v i o u r .

A s a f i rst s t ep , w e c h o s e to i n v e s t i g a t e c o m p o u n d s w i t h R = Y b so t h a t 1 7 0 Y b M ö s s b a u e r s p e c t r o s c o p y m e a s u r e m e n t s c o u l d a l s o b e m a d e . T h i s h e l p s to o b t a i n a d e t a i l e d c h a r a c t e r ­i s a t i o n o f t h e c o m p o u n d ' s p h y s i c a l p r o p e r t i e s . H e r e w e d i s ­c u s s d a t a o b t a i n e d f o r Y b 2 T i 2 0 7 a n d Y b 2 G a S b 0 7 . W h e r e a s Y b 2 T Í 2 Ü 7 i s w e l l o r d e r e d c r y s t a l l o g r a p h i c a l l y o n b o t h sub-l a t t i c e s , Y b 2 G a S b 0 7 i s d i s o r d e r e d o n t h e ( n o n - m a g n e t i c ) s e c ­o n d sub- l a t t i c e . F o r b o t h c o m p o u n d s , t h e Y b 3 + i o n c r y s ­t a l field g r o u n d s ta te i s a v e r y w e l l i s o l a t e d K r a m e r s d o u ­b l e t w i t h a p l a n a r a n i s o t r o p y , g^_/gz — 2.5 w h e r e gz a n d g± a r e r e s p e c t i v e l y t h e s p e c t r o s c o p i c f a c t o r s a l o n g a n d p e r ­p e n d i c u l a r t o a l o c a l [111] a x i s . T h e n e t i n t e r - i on i c i n t e r ­a c t i o n i s f e r r o m a g n e t i c i n Y b 2 T i 2 0 7 a n d a n t i f e r r o m a g n e t i c i n Y b 2 G a S b 0 7 . S p e c i f i c h e a t m e a s u r e m e n t s [1] h a v e e v ­i d e n c e d a s h a r p a n o m a l y ( t h e A t r a n s i t i o n ) a t ~ 0.2 K f o r Yf>2TÍ2 0 7 a n d n o a n o m a l y f o r Y b 2 G a S b 0 7 . I n b o t h c a s e s , t h e s h o r t r a n g e c o r r e l a t e d Y b 3 + m a g n e t i c m o m e n t s o f 1.1 5/XB

a r e o r i e n t e d ~ 45° to t h e l o c a l [111] a x i s .

F o r Y b 2 G a S b 0 7 , o v e r t h e w h o l e i n v e s t i g a t e d t e m p e r a ­t u r e r a n g e ( f r o m 21 m K u p to 200 K ) t h e l o n g i t u d i n a l m u o n p o l a r i s a t i o n f u n c t i o n , Pz(t), i s w e l l m o d e l l e d b y a n e x p o ­n e n t i a l f u n c t i o n . T h e r e f o r e t h e s p i n - d y n a m i c s as o b s e r v e d b y t h e s e m e a s u r e m e n t s a r e d e s c r i b e d b y a m u o n sp in- l a t t i c e r e l a x a t i o n r a t e , Xz. W e p r e s e n t XZ(T) i n F i g u r e 1. G o i n g d o w n i n t e m p e r a t u r e , w e f i rs t n o t e t h e s l o w i n g d o w n o f t h e fluctuations s t a r t i ng a t ~ 2 K , f o l l o w e d b y a s a t u r a t i o n b e l o w ~ 0.1 K . T h e s h o r t r a n g e c o r r e l a t e d Y b 3 + s p i n s t h u s c o n t i n u e to fluctuate as T —> 0.

N

i 1.5 -

fa C O

« X « DC

£ 1.0 -

0.5

0.0 -

I— I— I— I

* $ Yb2GaSbO?

• • 10 mT o 25 mT

_1_ _l I

0.01 0.1 1 10 Temperature (K)

100

The behaviour of Y b 2 T i 2 0 7 is far more complicated. In Figure 2 we display some spectra. Whereas for T > 0.275 K, Pz (t) is properly analysed with an exponential function, at lower temperature the shape of Pz (t) changes drastically. As indicated in Figure 2, at 0.20 K, i.e. below the temperature of the known specific heat A-transition, there is no long range magnetic order. We find the transition rather corresponds to a first order change from a regime where the Y b 3 + spin fluc­tuation rate, in the G H z range, follows a thermal excitation law and Pz{t) is an exponential function towards a quan­tum fluctuation regime with a rate, in the M H z range, which is temperature independent and where Pz {t) approximately follows a Kubo-Toyabe dependence.

Yb 2 Ti 2 0 7

B„. = 2 mT

0.00 -ih. 6 8 10 0.0

Time t (us) 0.5

Figure 2: /xSR spectra recorded for Y b 2 T i 2 0 7 . Panel a: /xSR spectra recorded at ISIS in a longitudinal field of 2 mT. Panel b: short time part of a /xSR spectrum recorded at PSI. This data extends to earlier times than does the ISIS data and clearly shows there are no short time oscillations confirm­ing the absence of long range order. The slight difference visible between the ISIS and PSI data at 0.200 K reflects the different temperature and magnetic field history in the two experiments pointing to the first order character of the transi­tion. For the two panels, the solid and dashed lines are fits to the Gaussian-broadened-Gaussian and Kubo-Toyabe models, respectively.

We have also studied G d 2 T Í 2 0 7 and G d 2 S n 2 0 7 . For each compound, we detect the magnetic phase transition seen near 1 K by 1 5 5 Gd Mössbauer measurements. The analysis sug­gests that G d 2 T i 2 0 7 has an incommensurate magnetic struc­ture and as expected for frustrated magnets, there are low-energy magnetic excitations. The response in G d 2 S n 2 0 7 is different from that in G d 2 T i 2 0 7 but low-energy magnetic ex­citations are still present.

REFERENCES

F i g u r e 1: T e m p e r a t u r e d e p e n d e n c e o f t h e m u o n sp in- l a t t i c e

r e l a x a t i o n r a t e Xz a s m e a s u r e d f o r Y b 2 G a S b 0 7 .

[1] H . W . J. B l ö t e , R. F. W i e l i n g a , W . J. H u i s k a m p ,

P h y s i c a 43, 549(1969).

77

ANOMALOUS TEMPERATURE DEPENDENCE OF THE MUON-SPIN RELAXATION IN

5-4-10INTERMETALLIC COMPOUNDS

G. J. Nieuwenhuys1, F. Galli1, J. A. Mydosh1, R. H. Heffner2, D. E. MacLaughlin3, O. O. Bernai4

RA-94-03, LEIDEN 1 - LANL 2 - RIVERSIDE3 - CALIFORNIA STATE LA 4

Metallic compounds with f-electron magnetic ions are of great interest because of their anomalous magnetic behav­ior. Rare-earth ions form good localized moments, leading in itself to fascinating magnetic ordering phenomena. How­ever, sometimes nature surprises us by combining magnetic ordering with properties of the conduction electrons, such as superconductivity, or changes in the lattice such as periodic displacements of the atoms, or even with a combination of the two, a charge-density wave.

The series RE5JJ-4SÍ10 of tetragonal compounds have re­ceived attention over the last decade due to this very combi­nation of ordering phenomena [1]. All compounds crystal­lize in the space group P4/mbm. The compound Lu5lr 4 Siio shows a transition to a commensurate charge-density wave at 83 K and becomes superconducting below 3.9 K [2]. The isostructural compound Er5lr 4 Siio shows upon cooling a tran­sition to an incommensurate periodic lattice distortion or charge-density wave at 155 K followed by a lock-in transition into a commensurate distortion at 55 K, to be completed by a transition to an antiferromagnetic state below 2.8 K [3, 4]. High intensity x-ray diffraction proves that this antiferromag­netic state coexists with the periodic lattice distortion [5].

We have measured the zero-field muon relaxation-rate as a function of temperature for polycrystalline and single-crystal Er 5Ir4Siio. For comparison we have also investigated the Er 5Ir4Geio, which does show an antiferromagnetic tran­sition at 8 K, but does not show any periodic lattice distor­tions or charge-density waves. Both results are displayed in Fig. 1 as rate times temperature versus temperature, since it appeared that the relaxation rate of Er 5Ir4Geio is propor­tional to 1/T. The two charge-density waves are clearly re­vealed in the results for Er5lr 4 Siio-

1000

800

400

200

O O O

O O

• E r J r Si

5 4 10 E r J r „ G e , „

5 4 10

J oo • • • • •<B??g g • • n° D ° D

50 100 150

T[K] 200 250 300

Hartmann et al. [6] have calculated the relaxation rate for magnetic compounds. The result leads to the following expression:

T J(J + 1) Y'2 + -(IfkNF(0))2kBT (1)

Here Ifk describes the interaction between the Er-4f elec­trons and the conduction electrons and is Np (0) the density of states at the Fermi level. The present experimental re­sults show that the relaxation is dominated by the Korringa (proportional to 1/T) term. In Er5lr 4 Siio this term increases when the first (incommensurate) transition occurs; it keeps increasing down to the lock-in transition, after which it in­creases even faster with decreasing temperature. Most prob­ably this has to be ascribed to changes in the density of states at the Fermi level.

Presently, bandstructure calculation are being carried out, which hopefully will confirm our riSR observation.

REFERENCES

[1] H. D. Yang, P. Klavius and R. N. Shelton, Phys. Rev. B 43,7688 (1991).

[2] B. Becker et ai, Phys. Rev. B 59,7266 (1999).

[3] F. Galli et ai, Phys. Rev. Lett. 85,158 (2000).

[4] F. Galli et al.,

Phys. Rev. B 62, 13840 (2000).

[5] F. Galli et al., to be published.

[6] O. Hartmann et al., J. Phys. F: Met. Phys. 16, 1593 (1986).

Figure 1 : The relaxation rate times temperature as a function of temperature for Er 5Ir 4Geio and for Er 5Ir 4Siio

78

l¿SR STUDIES ON GIANT MAGNETORESISTIVE Coo.05Cuo.95

G. M. Kalvius1, E. Schreier1, D. R. Noakes2, R. Wäppling3, U. K. Rössler4, K. Nenkov4, K.-H. Müller4, B. Idzikowski5

RA-01-14, TU MÜNCHEN 1 - VIRGINIA STATE2 - UPPSALA 3 - IFW DRESDEN 4 - POZNAN 5

Granular metals produced from immiscible alloys with a ferromagnetic component (e.g. a few at.% of Co in Cu) are of considerable interest due to their giant magnetoresistance arising from magnetic scattering of conduction electrons at the ferromagnetic precipitates of a few nanometers diameter. The magnetic properties of those systems are often discussed in terms of superparamagnetism of free clusters, but recent ac-susceptibility studies have found spin-glass-like proper­ties [1] which need the presence of frustrated magnetic cou­plings between the precipitates. For a deeper insight into the magnetism of such systems, ZF, LF, and TF pSR experiments were carried out between 2 K and 250 K at the GPS facility. We discuss the results for a sample with 5at.% Co in Cu, produced by melt spinning and annealed for 8 h at 480 °C. Similar studies for different Co concentrations (lat.%,2at.%) and various annealing times (2 h - 72 h) are under way.

S Ä 2 0 K

5kG 2kG

1kG

500G

0

0.0 0.5 1.0 1.5 2.0 2.5 3.0

Time (¡is)

Figure 1: ZF and LF spectra at 5K and 20K. For discussion of fit functions see text.

On the basis of the temperature dependence of pSR spec­tral shape one may distinguish three regions. In the low tem­perature regime (T < 15 K) the ZF and LF spectra can well be described by a Lorentzian Kubo-Toyabe relaxation func­tion (LKT) as shown in Fig. la. At base temperature (1.75 K) the LKT is essentially static, with rising temperatures it be­comes weakly dynamic (see plot of 1/r in Fig. 2). Simul­taneously one observes a decrease of the HWHM ULKT of the Lorentzian field distribution sensed by the muons (in fre­quency units) (see Fig. 2). At T > 1 5 K the spectra exhibit monotonie decay of polarization. 15 K is the temperature where \ a c for this sample attains its maximum. The attempt to fit the spectra at 20 K with a dynamic LKT failed badly, especially in LF (Fig. lb). Since 15 K could be a spin glass transition we next attempted to fit the ZF spectra at 20 K and above with the fast dynamic relaxation function derived in [2] within the Edwards-Anderson (EA) model. Its physical

base is that the local field at each muon site has a static and a fluctuating component, the former being the result of a finite order parameter in the spin auto-correlation function. The EA relaxation was unable to reproduce simultaneously the fast initial decay and the slow decay at late times. From extensive spectral simulations the cause of this failure be­came apparent, that is, the EA relaxation necessarily being the product of a static LKT and a dynamic root exponential component. In contrast, a sum function of dynamic LKT and root exponential relaxation (oc exp[—XSG i ] 0 ' 5 ) worked, in­cluding LF spectra (see Fig. lc). With rising temperatures the LKT fraction rapidly diminishes (see Fig. 2). This ap­proach implies inhomogenous spin freezing. Above ~200 K the relaxation is pure root exponential. The rate XSG remains rather temperature independent around 1.5 ps~4.

C ° 0 . 0 5 C U 0 . 9 5

100

80

: 60

. 40

20

0

• t t t 1 r

•

i-rri ¡

-•-rb 1—1— 1 1—1—

•2 .0A^ i\ •1.5 ^

"•1.0 \

i \ ! c

X A

I) •0.5 ^ p

À\ ÈL a L K T

•o.o°-

1 10 100

30

20

10

T e m p e r a t u r e (K)

Figure 2: Spectral parameters of the LKT fraction (see text).

In summary, the system shows freezing into a spin glass state below 15 K with the precipitates acting as the randomly distributed spins. The static width ULKT is more than an or­der of magnitude larger than in classical spin glasses with single ion moments, reflecting the larger spin cluster mo­ments. The reduction of ULKT with rising temperatures indi­cates the onset of spin dynamics within the clusters, lowering the effective cluster moment by motional averaging. The in-homogenous freezing between 20 K and 200 K most likely reflects the size distribution of precipitates and/or strong het­erogeneity in the spatial arrangement of the magnetic clus­ters. The rather large value of XSG means that fluctuations of cluster spins are still slow even close to room temperatures. The cause are persistent correlations between those spins. A state of free cluster moments is not reached.

REFERENCES

[1] B. Idzikowski et al, Europhys. Lett. 45,714 (2000).

[2] Y. I. Uemura et al, Phys. Rev. B 31, 546 (1985).

79

INTERLAYER EXCHANGE COUPLING IN Fe/Ag/Fe STUDIED BY LE-//SR

H. Luetkens1*2, M. Birke1, E. M. Forgan3, H. Glückler2, R. Khasanov2*6, H. H. Klauss1, J. Korecki5, F. J. Litterst1, E. Morenzoni2, Ch. Niedermayeri, M. Pleines2'11, T. Prokscha2, T. Slezak5, A. Suter2

BRAUNSCHWEIG1 - PSI 2 - BIRMINGHAM3 - KONSTANZ4 - KRAKOW5 - ZÜRICH6

Since the first observation of antiferromagnetic coupling of Fe films separated by a Cr spacer by Grünberg et al. [1] the interlayer exchange coupling (IEC) has been subject of intense research over the last few years. The discovery of os­cillations in the IEC as a function of spacer-layer thickness by Parkin et al. [2] has led to an increased interest in this field o f research. Much experimental efforts have been done to measure precisely the strength and period of the IEC in various systems and a remarkable agreement between theo­retical results and measurements have been achieved, e.g. see [3]. Nevertheless, the vast mayority of the experimental tech­niques used to study the IEC probe the ferromagnetic layers and very little is known about the induced spin polarization in the non-magnetic layer which mediates the coupling.

Low Energy muon spin rotation (LE-/xSR [4]) was used to investigate the oszillating spin polarization in the Ag layer of a 4 nm Fe / 20 nm Ag / 4 nm Fe trilayer. With this sensitive method the magnetic field distribution in the spacer can be obtained with high precision and compared to theory.

The first and most inductive approach to describe the IEC has been the so-called RKKY model. Originally the RKKY interaction describes the coupling of localized magnetic im­purities in a non-magnetic metallic host. The indirect ex­change coupling between the magnetic ions is mediated by a spatially oszillating conduction electron spin polarization of the metal. By proper summation, the RKKY interaction can easily be extended to the coupling of two monoatomic magnetic planes embedded in a non-magnetic metall. The coupling can be related to the topology of the Fermi surface of the spacer material. According to this theory the period of the Oszillation is determined by critical spanning vectors, qc, nested in the Fermie surface. Each of these spanning vectors lead to a different oscillation which have to be superimposed. The attenuation of the coupling is given by the curvature of the Fermie surface at the end points of qc-

Therefore, in the framework of the RKKY model, an ef­fective coupling of the two magnetic planes through a non­magnetic spacer is described as:

with

U = -J(d) M i • M 2

J(d) oc 2 ^ - cos(<^ d + >

(1)

(2)

Here, M¡ is the magnetization of the ferromagnetic layers, J the coupling constant, d the distance between the layers with the exponent (p¿ < 2). Following this approach, the expected field distribution seen by the muon can be calcu­lated assuming B(x) oc J{x). We have convoluted the spa­tial field distribution, B(x), with the muon stopping profile, P(x), shown together in Fig. 1. P(x) has been calculated with the Monte Carlo Code TRIMSP [5] for muons with a kinetic energy of 3 keV which we used in the experiment.

-> x

Figure 1: Muon implantation profile P{x) and calculated spatial field distribution B(x).

100 150 200 Field S (G)

300

Figure 2: LE-/xSR data together with simulation based on the RKKY model.

In Fig. 2 the measured LE-/xSR data together with the simulated probability function P(B) is shown. Detailed ana­lysis is in progress but the main features of P(B) can already be explained by the RKKY model.

REFERENCES

[1] P. Grünberg et al., Phys. Rev. Lett. 57, 2442 (1986).

[2] S. S. P. Parkin et al., Phys. Rev. Lett. 64, 2304 (1990).

[3] M. D. Stiles, J. Magn. Magn. Mat. 200, 322 (1999).

[4] E. Morenzoni, Appl. Magn. Reson. 13, 219 (1997).

[5] W. Eckstein, Computer Simulation of Ion-Solid Interac­tions (Springer Verlag, Berlin, 1991).

80

MAGNETIC FLUCTUATIONS IN ABX 3 HALIDES

P. C. M. Gubbens1, P. Dalmas de Réoñer2, A. Yaouanc2, S. Sakarya1, D. Visser1

RA-00-08, DELFT 1 - CEA GRENOBLE 2

The effects of geometrical frustration on the magnetic or­dering process is a very active field of research. Last year we reported measurements performed on the hexagonal com­pound CsNiBr 3 [1]. Critical paramagnetic fluctuations were found. Therefore frustration does not quench these fluctua­tions, in contrast to the conclusion of a previous NMR work [2].

We have attempted in October 2001 to extend our inves­tigation of the effect of frustration to CsMnBr3. This com­pound forms a three dimensionally ordered magnetic struc­ture below T N = 8.23 K. The magnetic moments are oriented at 120° to each other in the basal plane. This structure arises from geometrical frustration. This compound offers the pos­sibility to probe the effect of chirality on the magnetic fluc­tuations [3].

Playing with the spin rotator, we have performed mea­surements with the initial muon beam polarization, S M , either parallel or perpendicular to the c axis. Below T N , we have not detected any wiggles from the spontaneous local field at the muon site. We interpret that result as arising either from a large field distribution at the muon site or a too large max­imum magnetic field from a modulated magnetic structure. This is in contrast to our previous finding for CsNiBr3 for which the signature of the modulated magnetic structure was found.

In fact, from the pSR technical point of view, this com­pound is difficult. Even in the paramagnetic region, asymme­try is missing for S M 1 c and S M || c. We present in Figure 1 two spectra recorded at 80 K, i.e. far above T N . The spectra are the weighted sum of at least two exponential functions.

We still have to complete the analysis of all the spectra. However, from the presently available results, we already know that it will be difficult to extract quantitative infor­mation from the measurements, simply because of the large damping. Again, this is in contrast to the results obtained previously for CsNiBr 3.

REFERENCES

[1] P. C. M. Gubbens etat, PSI Sei. Rep. 2000,1,67 (2001).

[2] S. Maegawa, Phys. Rev. B 51,15979 (1995).

[3] H. Kawamura, J. Appl. Phys. 63, 3086 (1998).

1—i—i—i—i—j—i—i—i—i—j—i—i—i—i—j—i—i—i—r

0 1 2 3 Time (L IS )

T — 1 — i — 1 — i — 1 — i — 1 — i — 1 — i — 1 — r

j i i i i i i i i i i i L 0.0 0.2 0.4 0.6 0.8 1.0 1.2

Time (L IS )

Figure 1:

Two examples of spectra recorded on a single crystal of CsMnBr3. The direction of the initial muon beam polariza­tion, S M , relative to the c axis is indicated for each spectrum. The spectra have been recorded above the Néel temperature of 8.23 K. The fit presented in the upper panel involves the weighted sum of two exponential relaxation functions. The fit displayed in the lower panel is done with a single expo­nential relaxation function. However, it does not describe the data very well. Two exponential functions are needed to get a good description of that spectrum.

81

MUON-SPIN ROTATION AND MAGNETIZATION STUDY OF METAL-ORGANIC MAGNETS

BASED ON THE DICYANAMIDE ANION

S. J. Blundell1, F. L. Pratt1, Th. Jestädt1, M. Kurmoo3,1. M. Marshall1, K H. Chow4, C. M. Brown5, A. Lappas5, K Prassides5

RA-93-06, OXFORD1 - ISIS 2 - STRASBOURG 3 - LEHIGH4 - SUSSEX 5

In recent years there has been a growing effort aiming to understand molecular-based magnets and to obtain novel molecular magnetic materials with high transition temper­atures [1]. There is also a strong drive towards engineer­ing materials with combined optoelectronic and magneto-optical properties. The dicyanamide ion, [ N = C - N - C = N ] ~ , has been found to be a promising choice as a ligand in as­sembling novel metal-organic ferromagnets and ferrimagnets (see Ref. [2, 3, 4]) because it aligns divalent transition metal ions in such a way that their magnetic orbitals are approx­imately orthogonal. It is a small ligand and so can give rise to well defined structures with large orbital overlaps. It contains delocalized n electrons which enhance indirect exchange (principally superexchange) between metal sites. In our work, we have concentrated on the pure metal com­plexes, M n [ N ( C N ) 2 ] 2 , containing M 1 1 = Ni (d 8 , S = 1), M 1 1

= Co (d 7 , S = 3/2) or M 1 1 = Mn (d 5 , S = 5/2). (Only the Co sample is included in this report.) X-ray diffraction [3] and neutron scattering experiments [5] suggest that these com­pounds are isostructural, and that they adopt an orthorhombic form of the rutile structure [2,3] similar to those of CrCl2 and CuF 2. For the Ni and Co materials, the ground state is fer­romagnetic. Below the ferromagnetic transition temperature the spins are ordered collinearly [5] with magnetic moments of 2.61 pB (Co[N(CN) 2] 2) and 2.21 /x B (Ni[N(CN) 2] 2) ori­ented along the c-axis.

0.0 1 • • ' ' • • • 1 • • ' u

0.0 0.1 0.2 0.3 t (fjs)

Figure 1 : Temperature dependence of the muon asymmetry A(t) for Co[N(CN) 2 ] 2 . The inset shows the temperature de­pendence of the fitted muon precession frequency which is proportional to the internal field at the muon site.

We have fitted our measured asymmetry of Co[N(CN) 2 ] 2

for T < TQ (Figure 1) by the expression

A(t) = A±e~x±t cos(2?7i/i + <p) + Aye -*"* + Ahg (1)

where <p is a phase factor and v = jßB/2n is the Larmor precession frequency and B is the magnetic field at the muon

site. For the fits in the ordered temperature region we have also kept A±/A\\ = 2 fixed. This is because in a polycrys-talline sample, | of the signal is due to regions in which the local field is perpendicular to the initial muon-spin polariza­tion, and I of the signal is due to regions in which the local field is parallel to the initial muon-spin polarization. The fits were performed over the restricted time range from 0 /xs to 0.5 /xs.

We find [6] that the temperature dependences of the re­laxation Aj_ and the oscillation frequency v are similar, and that the inhomogeneous linewidth X±/2niy is approximately constant in the magnetically ordered regime. This might in­dicate that the large damping of the oscillatory signal is due to static depolarization and has its origin in the presence of various muon sites. Because of the very strong damping, functional forms other than Equation 1 could fit the data. Nevertheless, it is clear from the minimum in the lowest tem­perature data shown in Figure 1 that a quasistatic field does develop at the muon site in the ordered state.

The average magnetic field at the muon site as T —y 0 is found to be ~ 0.05 T. We can rule out a muoniated radi­cal state because of longitudinal field data [6], but a number of diamagnetic muon sites in the crystal structure could be possible. However, some dynamic relaxation is also present, since the non-oscillatory component is also relaxing. The damping rates are much larger than those that are found in purely organic magnets, due presumably to the presence of these dynamical effects. Further details on these experiments can be found elsewhere [6].

REFERENCES

[1] O. Kahn (editor), Magnetism: A Supramolecular Func­tion, NATO ASI, Vol. C484, (1996).

[2] S. R. Batten, P. Jensen, B. Moubaraki, K. S. Murray and R. Robson, Chem. Commun. 439, (1998).

[3] M. Kurmoo and C. J. Kepert, New J. Chem. 22, 1515 (1998).

[4] J. L. Manson, C. R. Kmety, Q. Huang, J. W. Lynn, G. M. Bendele, S. Pagóla, P. W. Stephens, L. M. Liable-Sands, A. L. Rheingold, A. J. Epstein and J. S. Miller, Chem. Mater. 10, 2552 (1998).

[5] C. R. Kmety, J. L. Manson, Q. Huang, J. W. Lynn, R. W. Erwin, J. S. Miller and A. J. Epstein, Phys. Rev. B 60, 60 (1999).

[6] T. Jestädt, M. Kurmoo, S. J. Blundell, F. L. Pratt, C. J. Kepert, K. Prassides, B. W. Lovett, I. M. Marshall, A. Husmann, K. H. Chow, R. M. Valladares, C. M. Brown and A. Lappas, J. Phys.: Condens. Matter. 13, 2263 (2001).

82

FINITE SIZE EFFECTS IN SINGLE LAYER SPIN GLASS FILMS STUDIED BY LOW ENERGY MUON SPIN RELAXATION

G. J. Nieuwenhuys1, M. B. S. Hesselberth1, F. Galli1, J. A. Mydosh1, E. Morenzoni2, N. Garifianov2'5, R. Khasanov2'4, H. Luetkens2'3, T. Prokscha2, A. Suter2

LEIDEN 1 - PSI 2 - BRAUNSCHWEIG3 - ZÜRICH4 - KAZAN 5

The freezing of magnetic moments in spin glasses [1] is expected to depend on the sample dimension. For instance, dc-magnetic susceptibility measurements have shown that the apparent spin freezing temperature decreases as the spin glass film thickness is reduced [2]. In order to obtain large enough macroscopic signals most of the measurements in­vestigating finite size effects have been performed on multi-layered films, where the spin glass material is alternated with decoupling layers. The main result of these studies is that freezing decreases down to zero as a critical thickness of about 1 nm is reached. In view of the concentrations of magnetic constituents used, this thickness corresponds with a monolayer of magnetic ions, and thus with a two dimen­sional spin glass. Bulk freezing (as shown via a peak in the ac-susceptibility) is still found in samples of 10 nm.

Polarized muons, which act as microscopic probes of lo­cal moment dynamics, are very well suited for the study of spin glasses, because of their high sensitivity on the appro­priate time window of magnetic fluctuations. By measuring the muon spin relaxation, spin glasses have been investigated by a number of groups [3]. However, up to now, these studies were restricted to the bulk, due to the high energy of the im­planted muons. This limitation has been overcome by the re­cent development of a tunable beam of low energy polarized muons, which can be stopped in materials at variable depths between a few nm up to several hundred nm [4]. We have used this technique to investigate finite size effects in single-layer AuFe, CuMn and AgMn spin glasses. Muon spin relax­ation also probes the dynamics of the magnetism in the sys­tem. The result of these experiments is that already at 20 nm thickness the spin freezing drastically changes character such that fluctuations persist down to the lowest temperature.

Positive muons with energies of 1, 2.5 and 6 keV were implanted in thin samples of AuFe 3 at.% (10,20 and 50 nm), in samples of CuMn 2 at.% (10,20 and 50 nm) using energies of 1.5,2.5 and 7 keV, and in AgMn 5 at.% of 20 nm thickness using an energy of 2.5 keV. The relaxation rate was measured as a function of temperature. In all cases a transverse field of 10 mT was applied to easy the data analysis. Such a magnetic field is too weak to seriously influence the spin freezing over a large temperature range. The result for the thickest sample is very similar to that obtained in bulk samples, also when only the top surface is investigated by using 1 keV muons.

We find for thinner samples not only the expected de­crease of the freezing temperature, but also that the relax­ation rate does not become as large as for the bulk sample (see Figs 1 and 2), reflecting fluctuations to persist down to the lowest temperatures. This result implies that the charac­ter of the spin glass freezing changes dramatically, when one dimension of the sample becomes smaller than about 20 nm.

Ä AuFe 3 at.%

° • • a 10 nm O 20 nm A 50 nm

— 1 1 1 1 1 1 1 1 1 —

0 10 20 30 40 50 T [ K ]

Figure 1: Relaxation rate for AuFe 3 at.% films as a function of temperature.

10-

3. 1:

0.1

1 CuMn 2 at.%

* * t fi * 6

o 10nm A 20nm V 50nm

e 10 20 30

T [ K ]

40 50

Figure 2: Relaxation rate for CuMn 2 at.% films as a function of temperature.

It indicates that for the thinner samples the freezing is far from rigid, in spite of the sharp maximum observed in the ac-susceptibility in multi-layered samples.

REFERENCES

[1] J. A. Mydosh, Spin Glasses: an experimental introduc­tion (Taylor and Francis, London, 1993).

[2] G. G. Kenning et al, Phys. Rev. Lett. 59, 2596 (1987).

[3] Y. Uemurae/a/., Phys. Rev. B 31, 546 (1985).

[4] E. Morenzoni et al, Phys. Rev. Lett. 72, 2793 (1994).

83

OBSERVATION OF CONDON DOMAINS IN ALUMINIUM BY //SR SPECTROSCOPY

G. Soit1, V. S. Egorov2, C. Baines1, D. Herlach1, U. Zimmermann1

RA-94-14, PSI 1 - KURCHATOV2

Dia- and paramagnetic domains were detected in a pure single crystal of aluminium at temperatures T < 1 K and magnetic fields between 1 — 2 T. The domain transition, indicated earlier by the behaviour of helicon excitations in this metal, is thereby spectroscopically confirmed.

In sufficiently pure metal single crystals Landau orbital magnetism leads, at low temperatures, to a magnetic state with oppositely magnetized 'Condon' domains: an intrigu­ing, little explored structure for non-ferromagnetic materials. The key quantity for the formation of Condon domains is the differential magnetic susceptibility x{B) = dM/dB for the given direction and strength of the external magnetic field i f . At low temperatures x as a function of the average micro­scopic field B shows the well known de Haas - van Alphen (dHvA) oscillations. Should, however, the oscillating x{B) reach, in its ascending sections, values larger than 1/47T, the homogeneous magnetic state becomes unstable and dia- and paramagnetic regions appear [1 ,2] . In the domain state the occupation of Landau levels and thereby the magnetizations ±Mp in the two kinds of domains remain 'frozen' as the field H changes, only the volumes of the oppositely magnetized regions vary. In each dHvA oscillation cycle there is a phase transition from the homogeneous to the domain state and an­other one restoring the uniform state. Though each metal (or other, e.g., organic conductor) has, depending on its Fermi surface (FS) and the orientation of i f , characteristic regions in the (B, T) plane where domain formation can be expected, direct observation of the domain state was successful up to now only for the metals Ag, Be, Sn and Pb.

For the study of Condon domains / JSR proved to be a most adequate method [3, 4, 5]: the muons implanted into the bulk material measure the local field in each domain, and the method is well adapted to low temperature single crys­tal studies. The domain state has shown different character­istic features in Be, Sn and Pb, depending on the 'domain active' sections of each FS at different field ranges. As to aluminium, an earlier experiment [6] provided an important, even if indirect indication for domain formation: the temper­ature dependence of the frequency and damping of the heli­con excitations in Al showed a radical change at T ss 1.1 K, which could well be explained by the assumption of domains appearing below this temperature. The present ¡iSR data con­firm this, by giving direct evidence on the presence of do­mains.

The Al single crystal plate in the / J SR experiment was placed normal to the field iî | | [110] (demagnetizing factor n « 1). The domain sections of the dHvA periods are the peak regions in Fig. 1. Here the domain magnetizations ±MP

are not sufficiently large to make AB = &nMp < 6-8 G vis­ible as a doublet splitting in the frequency spectrum of the precessing muons, but the domain formation is nevertheless clearly shown by the periodic, abrupt line broadening.

The frequency F deduced from the data corresponds to the cross section of the 'arm'-like FS sheets cut normal to

their axes in the third BZ (a small deviation from F 7 5 (110) = 286 T arises from an angular offset of the sample).

0.20r

Figure 1: Damping rate A (line broadening) of the / J SR signal at T = 20 mK. The sharp peaks show domain formation with the period AH = H2/F = 36 ± 1 G, implying a frequency F = 278 ± 9 T for the 'domain-active' dHvA mode. This corresponds to mode 75 with FJ5 = 285.7 T.

By tuning the applied field at higher values, periodic do­main formation persists up to ss 1.8 T. Above this field a sec­ond, small amplitude oscillation appears superposed to the 75 mode. The origin of this is not clear: it can be a sign for domains generated by another dHvA mode with frequency F 7 3 = 1250 T, an oscillation predicted but not yet observed at this field direction in dHvA experiments. But it can also be an artifact, a modulation due to the non-ellipsoidal shape of the sample leading to a spatial inhomogeneity of M, which arises with the double frequency 2F7Q of the 76 mode.

REFERENCES

[1] J. H. Condon, Phys. Rev. 145,526 (1966).

[2] D. Shoenberg, Magnetic oscillations in metals (Cambridge University Press, Cambridge 1984).

[3] G. Soit C. Baines, V. S. Egorov, D. Herlach, E. Krasnoperov, U. Zimmermann, Phys. Rev. Lett. 76,2575 (1996).

[4] G. Soit, C. Baines, V. S. Egorov, D. Herlach, U. Zimmermann, Phys. Rev. B 59,6834 (1999).

[5] G. Soit, V. S. Egorov, C. Baines, D. Herlach, U. Zimmermann, Phys. Rev. B 62, Rl 1933 (2000).

[6] V. I. Bozhko, E. P. Volskii, JETP Lett. 26, 223 (1977).

84

piSR IN II-VI SOLAR CELL MATERIALS

N. Ayres de Campos1, J. M. Gil1, H. V.Alberto1, R. C. Vüäo1, J. Piroto Duarte1, S. F. J. Cox2, A. Weidinger3

RA-97-23, COIMBRA1 - ISIS 2 - HMI BERLIN 3

ZnO single crystal. The shallow donor muonium state found in ZnO was first studied in powder samples [1, 2, 3]. The full characterization of the hyperfine interaction param­eters requires, however, the study of this state in oriented single crystals. This was achieved by measuring the orien­tation dependence of the separation of the precession fre­quencies at 5 K on a high purity ZnO single crystal (Fig. 1): AÏSQ = 490(10) MHz, D = 310(10) MHz [4].

Figure 1 : Orientation dependence at 5 K of the line separa­tion of the precession frequencies attributed to the shallow-level Mu state in ZnO.

HgO powder. An anisotropic paramagnetic Mu with a hyperfine constant intermediate between that of Mußfj in Si and the shallow-level Mu state of CdS or ZnO was dis­covered last year in HgO (on a powder sample) at GPS [3, 5]. In order to better model the orientation averaging of the anisotropy below 50 K, and to characterize the changes of the paramagnetic lines along the ionisation process above 150 K, additional TF measurements at 4 kG were performed. The complete set of data is presented in Fig. 2, with the simple analysis considering an effective anisotropy of the para­magnetic muonium.

15'

£ io

rxuDbmmm a m O D,

HgO powder TF 4 kG

O Ô Q Ô O Ô 0 O

50 100 150

Temperature (K) 200

Figure 2: Change with temperature of the effective hyperfine interaction parameters of Mu in HgO powder: Isotropic part A j s o and effective asymmetry parameter Dt^.

CdTe. A deep-level Mu state is formed in CdTe simulta­neously with the shallow-level Mu state. It corresponds to a missing fraction in TF and is repolarised in LF [2]. Dynamic effects are revealed in LF spectra as a temperature and field dependent relaxation, present at temperatures as low as 4 K.

LF and TF measurements performed at temperatures be­low 1 K (in LTF) still show a missing fraction in TF. On the other hand, the relaxation rates in the LF spectra at fields above 100 G are much reduced at these low temperatures. The study of the initial steps of dynamics is envisaged with these low temperature dependence measurements.

ZnSe, ZnS. The chalcogenides ZnSe, ZnS and ZnTe do not present the shallow-level Mu state seen on other II-VI compounds. The largest fraction of asymmetry (80-90%) is missing in TF measurements. In ZnSe and ZnS at 2 K, a normal muonium precession frequency is seen in a frac­tion of the order of 8%. Evidence of important dynamic ef­fects is observed in high longitudinal fields as a fast relaxing component that accounts for the missing fraction [6], and in TF measurements (at ISIS), with changes in the amplitude, phase shifts and relaxations of the diamagnetic fraction peak­ing at around 70 K [7].

A few TF measurements were performed in 2001 at GPS on ZnSe at 50 K, 100 K and 200 K. These confirm the previ­ous observations on the diamagnetic fraction and show that changes occur as well on the normal muonium lines. A de­tailed temperature scan in TF measurements within the tem­perature range of the GPS cryostat is needed to probe the ex­pected involvement of the normal muonium in the dynamic behaviour.

REFERENCES

[1] S. F. J. Cox et al, Phys. Rev. Lett. 86, 2601 (2001).

[2] J. M. Gil et al, Phys. Rev. B 64, 075205 (2001).

[3] S. F. J. Cox et al, J. Phys.: Condens. Matter 13,9001 (2001).

[4] H. V. Alberto et al, Proceedings of the HF1-12 Conference, August 2001, to be published in Hyperfine Interactions.

[5] J. M. Gil et al,

J. Phys.: Condens. Matter 13, L613 (2001).

[6] J. M. Gil et al, PSI Sei. Rept. 2000,1, 81 (2001).

[7] J. M. Gil et al, RBI0499, ISIS 1999 Annual Report.

85

MUONS IN SULPHUR AND SELENIUM

/. D. Reid1, S. F. J. Cox2, C. J. Rhodes3, U. A. Jayasooriya4, U. Zimmermann5

RA-00-18a, UCL 1 - RAL 2 - LIVERPOOL3 - NORWICH4 - PSI 5

Repolarisation measurements at RAL suggested the ex­istence of a radical-like muon state in sulphur[l], but TF ex­periments at PSI found only two coherent diamagnetic states, one with high relaxation rates[2, 3]; ALC experiments gave a weak signal attributed to the AM = 1 resonance of a rad­ical with hfc ~233 MHz[2]. TF measurements in selenium powder showed similar signals with some quantitative differ­ences, while ALC studies revealed a stronger resonance than in sulphur[l]. In 2000 we aimed to investigate more system­atically the behaviour of muons implanted into S and Se.

Experiments used the GPD spectrometer in ¡iEl, with the new LN2-flow Chemistry Cryostat designed to operate above 500 K. Results for sulphur were similar to those previously obtained[3], the finer T scan showing that the "fast" relax­ation attains a broad maximum of ~ 5 0 / i t s - 1 around 270 K. Similarly, extended data were obtained in amorphous sele­nium (a-Se) pellets up to

0.2 • I 0.15

ID

< 0.1 k

3 Hi i t t . j . : • • • • •

• Slow Component • F1 Signal A F2 Signal • Total O Slow Component • Slow Component A Fast Component • Total O Total (liquid)

275

T(K)

Figure 1 : Muon signal amplitudes in melt-cooled c-Se.

0)

T(K)

Figure 2: Relaxation rates of the "fast" muon signals in melt-cooled c-Se: below 200 K - the radical-like signals Fl and F2; above 400 K - the coherent diamagnetic muon signal.

• TFc-Se (melt) OTFc-Se(xirm) • ALC a-Se AALCc-Se(xfrm)

T(K)

Figure 3: Radical hyperfine couplings inferred from muon-spin spectroscopy in Se: squares - ALC (powdered a-Se[l]); triangles - ALC (c-Se pellets from heated a-Se); diamonds -TF (melt-cooled c-Se); circles - TF (c-Se pellets).

360 K, where the sample underwent an exothermic tran­sition to a crystalline form (c-Se).

Most interesting, however, were results obtained in an­other form of c-Se, cooled slowly from the melt. At 300 K only a "slow" diamagnetic signal was seen but on cooling very-quickly relaxing signals were detected and resolved in time-space to be those frequencies expected from a radical with hfc ~220 MHz ! These signals were followed from 80 to 200 K with constant amplitude (Fig. 1) but rapidly-changing depolarisation rates (Fig. 2). The signals were also seen as broad peaks in FFT plots of the early parts of the histograms.

Hints of extremely quickly relaxing components were fi­nally resolvable above 400 K as a single diamagnetic com­ponent whose relaxation fell rapidly with T (Fig. 2). As in sulphur, all relaxation disappeared in the melt with 100% po­larisation contained in a non-relaxing diamagnetic signal.

Radical signals were also seen in transformed c-Se pellets below 200 K in GPS, although relaxations remained constant around 20 / i ts - 1 below 50 K. The pellets also showed ALC resonances; Fig. 3 compares hfc values from various mea­surements. Close agreement of results from different struc­tural forms strongly suggests that the radical is simple, e.g. SeMu, but obviously it can react into a diamagnetic species

much more quickly in disordered a-Se than in the c-Se forms.

REFERENCES [1] S. F. J. Cox et ai, Hyperfine Interactions 106, 85 (1997). [2] S. F. J. Cox and I. D. Reid,

Appl. Magn. Reson. 12, 227 (1997). [3] I. D. Reid and S. F. J. Cox,

Physica B 289-290,620 (2000). [4] I. D. Reid et ai, Magn. Reson. Chem. 38, S3 (2000).

86

MUONS IN SULPHUR AND SELENIUM

/. D. Reid1, S. F. J. Cox2, C. J. Rhodes3, U. A. Jayasooriya4, U. Zimmermann5

RA-00-18b, UCL 1 - RAL 2 - LIVERPOOL3 - NORWICH4 - PSI 5

In 2001 we continued to investigate the radical-like state found in crystalline selenium (c-Se) at low temperatures and the influence of sample preparation on this species. Results from GPS in December 2000 were noticeably different from earlier GPD observations with slightly higher relaxation rates which levelled off around 20 / x s - 1 below 50 K. Since the GPD results used c-Se cooled from the melt, while the GPS data were from amorphous (a-Se) pellets transformed into c-Se by heating above 360 K, we were particularly interested in investigating melt-cooled c-Se below 77 K and in the ALC spectrometer.

Unfortunately, a 7rE3 beamline failure prevented ALC experiments, but a melt-cooled c-Se sample suitable for the Janis cryostat was prepared using the new Chemistry cryostat as an oven. Measurements were made below 150 K and the data fitted to a diamagnetic component at vß and two radical­like signals, Fl and F2. Fig. 1 shows the relaxation rates of Fl and F2, compared with the earlier results; Fig. 2 similarly shows the derived hyperfine couplings, Aß=Fl + F2.

Fast Component relaxation in c-Se

Hyperfine Couplings in Selenium

• F1 (Solid, GPD) S F 2 (Solid, GPD) &F1 (Pellets, GPS) Í&F2 (Pellets, GPS) SDiairagnetic (Solid, GPD) « F1 (Solid, Janis) a F2 (Solidjanis)

f

tmf'm, • m • •

T ( K )

Figure 1: Relaxation rates of "fast" muon signals in c-Se: below 200 K - the radical-like signals Fl and F2; above 400 K - the coherent diamagnetic muon signal vß.

We now believe it unnecessary to invoke a complex series of chemical reactions to explain the apparent transformations between muoniated species in selenium - a simpler model in­volving spin-exchange fits the observations quite well. Fig. 3 (after Abragam[2]) shows the spectra seen when a system jumps between two signals ±r5 = ±120 MHz at various av­erage frequencies il. For small il there are sharp peaks at ±r5, of Lorentzian shape with width il. As il increases the peaks broaden and move towards zero; eventually the wing peaks disappear and a broad central (average) peak arises, sharpening as il further increases to become Lorentzian with a width S2/2il. To first order, muoniated radical frequencies are vß ± Aß/2; spin flip of the muonium electron (e.g. spin exchange with an unpaired electron) will flip the radical be­tween these states. Following the model in Fig. 3, as the rate

T ( K )

Figure 2: Radical hyperfine couplings inferred from muon-spin spectroscopy in Se: squares - ALC (a-Se powder[l]); triangles - ALC (c-Se pellets from heated a-Se); diamonds -TF (melt-cooled c-Se); open circles - TF (transformed c-Se pellets); filled circles - TF (melt-cooled c-Se in Janis).

il of this flip increases the width of the radical signals will increase while the apparent Aß decreases. At higher il the radical signal will disappear, until finally a fast-relaxing sig­nal (width A2

ß/8fi) appears at the average frequency, vß. We are currently developing this model to explain all the results seen in selenium, and have hopes that it can also elucidate our sulphur data.

Frequency (MHz)

Figure 3: Spectra of a system consisting of two frequencies ±120 MHz, jumping between the two at average frequencies fi = 1,10, 20,100,500,1000 and 5000 MHz.

REFERENCES

[1] I. D. Reid et al, Magn. Reson. Chem. 38, S3 (2000).

[2] A. Abragam, The Principles of Nuclear Magnetism (Oxford, 1961).

87

MEASUREMENT OF RELAXATION RATE AND PARAMAGNETIC FREQUENCY SHIFT OF

NEGATIVE MUON SPIN PRECESSION IN SILICON

T. N. Mamedov1, D. Andreica2, D. G. Andrianov3, V. N. Gorelkin4, D. Herlach2, A. V. Stoykov1, U. Zimmermann2

RA-97-25, DUBNA 1 - PSI 2 - MOSCOW 3 , 4

Our earlier measurements [1,2] suggested the existence of peculiarities in the behaviour of the frequency shift of negative muon spin precession in n-type silicon with a low impurity concentration and in p-type silicon with impurity concentration close to n c - the critical concentration cor­responding to the semiconductor-metal transition (the Mott transition). But the accuracy in determination of Alo/loq

(Alo = to(T) — loo, where loq is the muon spin precession frequency in a diamagnetic state of the MA1 acceptor center) was insufficient to conclude on a substantial deviation of the temperature dependence of the frequency shift from the 1 /T-Curie law.

Measurements carried out in 2001 were devoted to a study of the temperature dependence of A w / w q for silicon sam­ples with phosphorus (1.6 • 1 0 1 3 c m - 3 ) and boron (4.1 • 1 0 1 8 c m - 3 ) impurities. Compared with [1, 2] the present measurements were carried out in a wider temperature range and with about two times higher precision. We also per­formed preliminary measurements on polycrystalline Si and on samples under uniaxial stress.

The results give evidence for a substantially different be­haviour of the muon spin precession frequency shift in n- and p-type silicon (see Fig. la):

1) In a nondegenerate n-type silicon sample with phos­phorus impurity 1.6 • 1 0 1 3 c m - 3

A w / w q is inversely pro­portional to temperature at T < 50 K but drops to zero at T > 55 K, which may indicate close to unity probability of ionization of the MAl-acceptor at these temperatures.

Deviations from the Curie law of the temperature depen­dence of Alo/loo could also occur if the relaxation rate u of the magnetic moment of the acceptor center would be of the order of or higher than A/h, where A is the Zeeman splitting of the acceptor center energy levels in the magnetic field. In this case the frequency shift must also depend on the value of the external magnetic field, i.e. Alo/loq = f(T, H).

To find out which of the above mentioned mechanisms is responsible for the deviation of the temperature dependence of Ato/loo from the Curie law, both the temperature and mag­netic field dependence of Ato/too should be studied on sili­con samples with different donor impurity concentrations.

2) In contrast to n-type silicon, in a degenerate silicon sample with boron impurity (4.1 • 1 0 1 8 c m - 3 ) the behaviour of the frequency shift of the muon spin precession does not contradict the 1 /T-dependence at temperatures higher than ~ 50 K, while at T < 40 K there is a substantial deviation of Alo/too from the Curie law.

The temperature dependence of the muon spin relaxation rate A (Fig. lb) measured on the above discussed silicon sam­

ples confirm our earlier results [1, 2]. The present data for the degenerate p-type sample also suggest that A is likely to decrease with temperature at T < 10 K.

16-1

14-

12-

10-Ö

8-

3° 6-'S < 4 -

2-

0-

Sï.P [1.6*10 c m ]

Si:B [4 .1 *10 1 8 cm 3 ]

a)

I f

10 100

T, K

i o Si:P [1.6*10 cm ]

- Si:B [4.1*10 l acm~ 3]

b)

5 6 7 8 910 30 40 50 60 70

T, K

Figure 1 : Temperature dependencies of the frequency shift Alo/too (a) and the relaxation rate A (b) of negative muon spin precession in silicon for samples with phosphorus (1.6 1 0 1 3 c m - 3 ) and boron (4.1 1 0 1 8 c m - 3 ) impurities. The dashed lines serve as guides to the eye.

REFERENCES

[1] T. N. Mamedov, I. L. Chaplygin, V. N. Duginov et al, J. Phys.: Condens. Matter 11, 2849 (1999).

[2] T. N. Mamedov, D. G. Andrianov, D. Herlach et al, JETP Lett. 73, 674 (2001).

88

DYNAMIC SOLVENT EFFECTS PROBED BY MUONIUM IN AQUEOUS SOLUTION

R. Scheuermann, H. Dilger, E. Roduner

RA-01-26, STUTTGART

Kinetic isotope effects (the ratio of isotopomeric reaction rate constants) provide information on the reaction mecha­nism and serve for testing reaction rate theories. The H/D abstraction from the deuterated (DCOO - ) or undeuterated (HCOO - ) formate anion by Mu, H, or D atoms in aque­ous solution is a reaction which is sufficiently simple to al­low ab initio calculations of the structures and of vibrational frequencies and offers the possibility to study six isotopic variations of the anion or the attacking atom and a total of eight different reactions in two isotopomeric solvents (H2O or D2O) on the same potental energy surface. However, the only reactions directly comparable when investigating effects solely attributable to the solvent are those with Mu as the attacking atom. It has to be distinguished between equi­librium effects where the solvent is completely relaxed at all times along the reaction coordinate, and dynamic (non-equilibrium) effects where the solvent cannot follow the re­acting system in its motion across the reaction barrier, and the transition state is not embedded in a relaxed solvent (Kramers' solvent friction [2]).

In previous work [ 1 ] an excellent Arrhenius behaviour for the rate constants in H2O aqueous solution with large kinetic iso­tope effects in particular between Mu and its heavier isotopes was found (Fig. 1), the reaction with Mu being one order of magnitude slower. Calculations based on a simple equilib­rium solvation model which treats the solvent as a contin­uum dielectric predicted the experimental results for H and D reasonably well, and the corresponding energy barrier was entirely attributed to solvent effects. However, in the case of Mu some mismatch with the experimental data (too slow reaction and too low preexponential factor) remained, either due to the simplicity of the equilibrium solvation model or a significant contribution of non-equilibrium solvent effects. Therefore, the reaction of Mu with HCOO~ and DCOO~ (prehminary results) dissolved in D2O was studied. Ow­ing to its larger moment of inertia D 2 0 should relax more slowly and thus lead to a higher activation energy than H2O. However, both the activation energy and the preexponential factor turn out to be smaller in D2O than in H2O (Fig. 1), just opposite as expected if the solvent friction would dom­inate. Moreover, the preexponential factor in D 2 0 is even smaller than predicted from theory for the gas phase, a value which is actually an underestimation as the loss of solvation entropy related to the attacking hydrogen isotope is neglected and an eventual contribution from tunneling is not taken into account.

The new experimental results cannot be explained simply: according to ab initio calculations the barrier is solely deter­mined by the polarisation of the solvent, therefore the very small difference in the dielectric constant of H2O and D2O does not affect the height of the barrier. Both a smaller pre­exponential factor as well as a lower activation energy would be expected if tunneling is favoured in D2O, but at present

there are no other indications why this should happen. A further enhancement of the solvent friction of D 2 0 comes from its 24% higher viscosity compared to H 2 0 and should even more increase the energy barrier. The present results demonstrate the high sensitivity of Mu. Obviously, our un­derstanding of dynamic solvent effects is still incomplete and a further development of theory is required.

• H C O O ' + D ( D 2 0 )

A H C O O + H ( H 2 0 )

O D C O O ' + D ( D 2 0 )

A D C O 0 + H ( H 2 O )

• H C O O + M u ( D j O ) (*)

• H C O O + M u ( H 2 0 )

O D C O O ' + M U ( D , 0 ) (*)

• D C O O ' + M u ( H 2 0 )

3.0 3.2 3.4 1000 KIT

Figure 1 : Arrhenius plot for the eight different reactions ac­cessible by isotopic substitution of the formate anion (pro-tonated or deuterated) or the solvent (light or heavy water). (*): this work, other data from [1].

12.5 n

R-H-Mu (*) R-D-Mu (*)

AS*/(J mol"' K"')

Figure 2: Experimental (symbols) and calculated (lines) Ar­rhenius preexponential factors plotted against the theoretical activation entropy (from [1], (*): this work). Full squares: HCOO"/H 2 0, squares: DCOO"/H 2 0. Full triangles: HCOO"/D 2 0, triangles: DCOO"/D 2 0.

REFERENCES

[1] A. M. Lossack, E. Roduner, D. M. Bartels, Phys. Chem. Chem. Phys. 3, 2031 (2001).

[2] H. A. Kramers, Physica (Utrecht) 7, 284 (1940).

89

LOCAL ENVIRONMENT OF COSURFACTANTS IN SURFACTANT BILAYER SYSTEMS

R. Scheuermann1,1. M. Tucker2, H. Dilger1, B. Beck1, E. Roduner1

RA-00 -21 , STUTTGART1 - UNILEVER RESEARCH PORT SUNLIGHT 2

Surfactants are ampiphilic molecules possessing both wa­ter soluble and oil miscible functional groups. When dis­solved in water at sufficiently high concentrations, self-aggre­gation leads to the formation of mesophases, e.g., regularly separated bilayer 'sheets'. The organisation or distribution of these 'sheets' governs the overall rheology of such lamel­lar systems, and this can be modified by changes in surfactant concentrations or by the addition of cosurfactants. Moreover, mixtures of surfactants are commonplace in order to achieve a desired performance characteristics, e.g., in detergency.

In this work avoided level crossing (ALC) pSR is used to determine the local environment of a muonium substituted radical derived from a cosurfactant in a dialkyl chain sur­factant system (DHTAC 1 ) and its affinity for the aqueous or non-aqueous environment at the bilayer interface. The polar­ity of the environment probed by the radical is quantified by the An resonance positions in water (polar, 100 % aqueous character) or liquid octadecane (non-polar, 0 %).

In previous work it was concluded that in the low-tempe­rature (Lß) phase the muonated cyclohexadienyl radical de­rived from 2-phenylethanol (PEA-Mu) resides preferentially in an aqueous environment, i.e., in the interstitial water sep­arating the bilayers, the close packing of the hydrocarbon chains preventing the radical to penetrate the bilayer. This changes at higher temperatures in the L a phase, where the 'molten' hydrocarbon chains now allow PEA to become in­corporated within the bilayer. Axial alignment leads to the appearence of additional A i resonances at lower fields. In or­der to better define a polarity scale a series of measurements of PEA in different alcohols and in methanol/water mixtures were performed. The results for PEA-Mu are shown in Fig. 1. With increasing hydrocarbon chain length (decreasing polar­ity) of the alcohols or increasing methanol concentration the resonance fields shift to lower field values.

vol. % methanol

carbon chain length (no. C atoms) of alcohol

Figure 1: Polarity of the environment of PEA-Mu in methanol/water mixtures (top) or different alcohols (bottom).

Systematic studies were extended using 3-hexen-l-ol as a cosurfactant. The signature of the ALC spectra obtained

12,3-diheptadecylesterethox-n-propyl-1,1,1-trimethylanimoniumcWoride

in solutions of water or octadecane is quite different (Fig. 2a). Whereas three resonances show up in water, only two resonances can be resolved in octadecane. The small dif­ference of the muon coupling constant of the two isomers (1 MHz at 35 °C in bulk hexenol) is not resolved in ALC experi­ments, the number of observed resonances therefore depends on the number of different proton couplings. The free ro­tation along a C-C bond dynamically averages the coupling constants of the protons involved, explaining the two Unes in octadecane due to two inequivalent sets of protons. In water the three lines can only be explained if three /3-protons be­come inequivalent, i.e., if they are locked in a rigid position with respect to the radical centre. This would correspond to a completely different conformation of the 4-hexyl radical in H 2 0 or C i 8 H 3 8 , a problem which has to be addressed in molecular dynamic simulations.

a) hexenoj/octadecane

Jrexenol/water

10500 11000 11500 12000

B[G] 12500 13000

Figure 2: a) A 0 resonances of hexenol in water or octade­cane. b) ALC spectra of hexenol in DHTAC; shift of the resonance positions is indicated by solid lines.

The ALC spectra obtained on a DHTAC/hexenol solu­tion are shown in Fig. 2b. In the Lß phase the A 0 signature is clearly of aqueous character (3 resonances), no A i reso­nances are observed. This is consistent with our interpreta­tion of the DHTAC/PEA data, the muonated radical residing in the aqueous layer. In the L a phase a concurrent change of A 0 signature combined with the appearence of A i res­onances is evidence of a change in hexenol local environ­ment. Furthermore it is consistent with hexenol incorpora­tion within the hydrophobic environment and axial alignment within the bilayer. This is consistent with previous data col­lected using PEA as a tracer. However, in this instance the interpretation is süghtly compücated by the third A 0 reso­nance when confined to aqueous environments.

90

A COMBINED AVOIDED LEVEL CROSSING - RADIO-FREQUENCY RESONANCE METHOD

N. M. Suleimanov1^, D. Herlach1'3, S. A. Moiseev2, R. G. Mustafin2, J. Cherix1, H-R. Fitze1, P. Sigg1

RA-01-28, PSI 1 - KAZAN 2

In a standard ALC experiment AM = 0 resonances occur at magnetic fields

J3R

2(7M - IN)

where AMU and AN denote the muonium and nuclear hy­perfine constants, and 7 M , 7 n the gyromagnetic ratios of the muon and the adjacent nucleus respectively (see, e.g. [1]). The normal way to assign a resonance line to a nuclear spin participating in it and to estimate the corresponding nuclear hyperfine constant is by computer simulation of the ALC spectra. As this method is model dependent and - especially in cases where several nuclei may be available as candidates for a nearest neighbour to the muon - a variation of many parameters has to be performed to assign the observed line.

We have proposed to combine ALC with radio-frequency (RF) techniques in order to excite transitions between mag­netic energy levels of muonium and nuclear spins involved in the avoided level crossing resonance and act upon the ampli­tude of the ALC resonance line. By means of this "RF-ALC" method the direct identification of the nuclei participating in a given ALC resonance should become possible.

A schematic view of the experimental RF-ALC set-up is shown in Fig. 1. The RF field is generated in a flat wide-band coil. The design of the coil (rectangular shape, dimensions

SC

F n

SC

A - G - R

to the initial muon polarization). The RF power source con­sisted of a FLUKE 606 A synthesized generator (G) and a 500 W wide-band ENI type A-500 amplifier (A), the out­put of which was directly connected to the coil by a 50 ohm coaxial cable. In order to monitor the magnitude of the RF field, a small one-turn pick-up coil was placed near the RF coil and connected to an oscilloscope (O).

First experiments were carried out on the non-conducting polymer polybutadiene (PBD) at ambient temperatures. Data were collected separately with RF-on or RF-off by using the standard ALC-iiSR data acquisition system. Measurements were performed in the frequency range 18.5-19.8 MHz at various levels of RF power. Fig. 2 shows some preliminary results of the test measurements. As may be seen the dif­ference (if any) between the RF-on and RF-off data is very small. However it is too early to draw any conclusions be­cause in the present set up, RF-on and RF-off runs were car­ried out separately with accumulation of large statistics, so that the experimental conditions during RF-on and RF-off runs may be different. Another problem is the heating of the sample due to eddy currents induced in the copper turns of the resonance coil by the RF field. In the case of PBD this caused an appreciable change of the position and form of the resonance line. By using substances in which the molecular dynamics effectively average the hyperfine anisotropy and a more sophisticated data taking system (where the RF-on and RF-off data are taken in short, alternating intervals at each magnetic field) we hope to be able to demonstrate the feasi­bility of the method in 2002.

3 2 -

3 0 -

2 8 -

2 6 -

2 4 -

2 2 -

2 0 -

1 8 -

1 6 -

1 4 -

3

CO <D

+¿ Q. E <

8 B., G

10 - r -

11 i

12

Figure 1 : Schematic view of the experimental RF-ALC set­up. SC: Superconducting solenoid. F, B: Forward and back­ward detector assemblies. O: Oscilloscope. R, G, A: RF Remote control, generator and amplifier.

5x5x0 .4cm 3 , 9 turns) was chosen to optimise the experi­mental conditions with regard to the given constraints (i.e. size of the beam spot, area shadowed by the turns of the coil, and the fact that the RF magnetic field B\ has to be perpen­dicular to the field of the superconducting solenoid (SC) and

Figure 2: Solid circles: RF-on amplitudes (arbitrary units) of the ALC resonance line as a function of RF field strength. Open circles: Corresponding RF-off amplitudes measured at the respective sample temperatures.

REFERENCES

[1] B. D. Patterson, Rev. Mod. Phys. 60, 69 (1988).

91

LOW ENERGY MUON DEVELOPMENTS

T. Prokscha1, R. Khasanov1'3, H. Luetkens1'2, E. Morenzoni1, A. Suter1, H. P. Weber1

PSI 1 - BRAUNSCHWEIG2 - ZÜRICH 3

In 2001, several developments served the constant effort to improve the low energy muon (LE-/X+) program. The base temperatures of the existing moderator and sample croystats were optimized by minimizing the thermal load: the interior surfaces of the cryogenic shields were blackened with CuS, and at the moderator and sample holder, thinner high voltage supplies were employed to decrease the thermal conductivity of the wires. A 6-mm sapphire electrically insulates the sam­ple holder from the cold finger. An optimum thermal conduc­tivity between cold finger and sample holder was achieved by putting 100-/xm thick indium foils between the sapphire and the metal pieces. Tests have shown that this is compat­ible with the UHV requirements of our apparatus. Specially shaped sapphire plates further improved the mechanical con­tact. The base temperatures amount to 6.3 K at the modera­tor, and 4.2 K at the sample holder. In both cryostats open­ings with an area of ~ 25 cm 2 are left to avoid absorption of the LE-/x +, thus giving rise to a non-reduceable load of thermal radiation from outside of the shields. For a further reduction of the sample temperature, a new UHV compatible continuous flow cryostat with a phase separator was devel­oped and built in collaboration with the PSI Low Tempera­ture Facility group (B. van den Brandt, S. Mango). Similar to the existing sample cryostat a sapphire plate is used for elec­tric insulation and the sample can be floated to ±12.5 kV. A sample temperature of 2.5 K was measured under normal experimental conditions.

The temperature of 6.3 K at the moderator allows now growing a stable solid neon (s-Ne) moderator which yields the highest moderation efficiency e M . Compared to a solid nitrogen (s-N 2) moderator, the use of s-Ne or solid argon (s-Ar) as a moderator is complicated by their instability against high voltage discharges. This was improved by replacing the 25-/xm gold-covered tungsten wires in the field defining ac­celerator grids by 50-/xm thick wires. This makes possible the use of s-Ar and s-Ne moderators for stable long term op­eration. We measured for the first time the thickness depen­dence of e M for a s-Ne moderator. A comparison between s-Ne, s-Ar and s-N 2 is shown in Fig. 1. The escape depths [1] amount to 250 nm, 35 nm and 15 nm, respectively. Adding a 10-nm layer of s-N 2 on top of a s-Ar or s-Ne layer im­proves the high voltage stability, and for s-Ar, e M is 15% larger than for a blank s-Ar layer. The maximum extraction voltage of a s-Ne/s-N 2 moderator is ~ 12 kV, whereas for a s-Ar/s-N2 moderator an extraction voltage up to 20 kV is possible. With this moderator we obtain a LE-/x + rate of ~ 670/s at the sample, and ~ 1600/s at the moderator. For s-Ne (12 kV extraction) the corresponding rates are ~ 750/s and ~ 2800/s, respectively. The surface muon rate on the beam counter (2.6 x 2.6 cm 2 ) in the 7rE3 area is estimated to 30 M/s (achromatic mode, Ap/p ~ 7%, 1.8 mA proton current, 6-cm target E). With the 4.2-cm thick target E the LE-/X+ rate is reduced by 25% - 30%.

o

- - A -

—A— —*--A—A— -A--*-

-À-

" A * A = N e

-A--À- • = Ar

- A-

• c£® A 0 = N 2

? / * A ^ A*

. 1 , . , , 1 . , , . 1 , , , , . . . . I . . . . I . . . . I . . . . I . . . . I . . . . I . . . . I . . . . I . . . . I . . . . 0 100 200 300 400 500 600 700 800 900

d (nm)

Figure 1: The moderation efficiency e M as a function of mod­erator thickness d for s-Ne, s-Ar and s-N 2 .

The migration of the old TANDEM data acquisition sys­tem to the new, portable MIDAS system [2] was performed in 2001, including the complete slow control system. Con­trol over the whole experiment is obtained through a Web browser interface. This allows simple operation, especially for new users, and remote control from in- and outside of PSI. The access to CAMAC is obtained via an CAMAC-PC interface. The frontend and backend computers consist of low-cost standard PC's running Windows 98/NT and Linux RH6.2. The computer busy (CB) time due to CAMAC read­out and data transfer was significantly lowered in event-by-event data taking mode. Compared to the TANDEM system the CB time is now four times smaller, thus allowing data tak­ing at higher rates. The old DEC terminal servers for reading and transmission of the slow control data were replaced by a modern Lantronix terminal server.

The LE-p+ apparatus will move in 2003 to the new ded­icated high intensity surface muon beam line in the pE4 area [3]. The installation of the new beam line is scheduled to start at the beginning of 2003. About 50% of this 2 MCHF investment is funded by contributions of the Technical Uni­versity of Braunschweig and the University of Konstanz via the German BMBF, and by contributions of the University of Birmingham (EPSRC) and the University of Zürich, and possibly by the Leiden University.

REFERENCES

[1] T. Prokscha et al,

PSI Sei. Rept. 2000,1,90 (2001).

[2] S. Ritt, http://midas.psi.ch.

[3] E. Morenzoni et al, PSI Sei. Rept. 2000,1,91 (2001).

92

93

L a b o r a t o r y f o r

M i c r o a n d N a n o T e c h n o l o g y Foreword

Nano Factory and X-ray Optics

Silicon Based Nanomaterials and Nanoelectronics

Molecular Nanotechnology

94

LABORATORY FOR MICRO- AND NANOTECHNOLOGY

/. Gobrecht

The year 2001 at the Laboratory for Micro- and Nano­technology (LMN) was characterised by significant scientific output on one hand and a focussing and redirecting of research activities on the other.

I am happy to report some of the scientific highlights here:

• A new process was discovered for the self-assembly of silicon quantum wells on pre-patterned substrates. Intense photoluminescence was observed from these structures.

• 68%-efficient linear zone-plates were realised for focussing of hard X-rays - to our knowledge a world record and of high relevance to X-ray microscopy and efficient use of synchrotron radiation in general.

• Real-time observation of electromigration effects on stress in aluminum interconnect lines were observed for the first time by synchrotron X-ray diffraction imaging.

• A novel mode of self-organisation for binary molecular mixtures in 2-d layers has been observed by high-resolution STM in co-operation with the University of Basel, revealing also some properties of the 2-d solid/gas phase equilibrium.

In the area of Si/SiGe nanomaterials important progress can be reported on developing the technologies and gaining the scientific insights which are necessary towards our long term goal of realising efficient light emission from silicon-based structures. In the area of micro and nanostructuring, activities were concentrated on either synchrotron X-ray related work or on co-operations with industry and universities ('base-lab' function).

The Molecular Nanotechnology group successfully concluded several projects during 2001. The "Nanojunc-tion-Lab" is nearly completed and two related proposals were submitted and passed evaluation. Additional effort was put in defining new projects showing a high degree of synergy to other PSI research priorities.

Joint work with industrial companies intensified in 2001. There were seven new projects funded and started within the priority program "TOP Nano 21" with a total number of 12 industrial and 9 academic partners. High-quality results were achieved in this "base-laboratory" area, some of which could not be reported on in this volume. The good progress in these projects is confirmed by the positive feedback from our partners. A success in technology transfer was the selling of one of our patent applications to a biochemical company in Switzerland.

The internal base-laboratory services saw among other things a significant increase of support by LMN in design and assembly of various detectors used for synchrotron- or space borne X-ray, heavy element or particle detection. Our aim for the future is to establish a closer co-operation and knowledge sharing between these various detector activities.

As can be seen from the above, a significant part of LMN's research activities has been redirected during 2001 towards use and application of synchrotron radiation. This is in view of the now completed Swiss Light Source at PSI which offers unique research opportunities, particularly when taking advantage of the synergies with the capabilities in micro- and nanostructuring of materials established at LMN. In fall of 2001, PSI approved a large proposal submitted by LMN in cooperation with the SLS and BIO departments and external partners on "templated self-assembly of nanomaterials" which will include the setting up of a beamline-split at SLS for X-ray interference lithography.

Another engagement of LMN towards research at PSF s large facilities is the start of a co-operation with SLS and DESY (Hamburg) on the project "Electro-optical auto­correlation interferometer for longitudinal electron beam analysis", the aim of which is the control and improvement of electron-bunch processes in new generation accelerators and light sources.

It is a great pleasure for me to report two awards obtained by LMN personnel: G. Dehlinger and L. Diehl were awarded the "IBM-Prize" of the Swiss Physical Society for their work on intersubband quantum-cascade light emission from Si-SiGe structures. Together with authors from the ENE dept., B. Bitnar, H. Sigg and G. Palfinger received the "best poster award" (out of over 600 posters displayed) at the 17111 European Photovoltaic Solar Energy Conference for their poster on advances in TPV-systems.

I would like to take the opportunity to thank all LMN staff for their engaged scientific work, for successful fund raising and for taking great care about our academic and industrial partners. Equally I thank the PSI directorate for the continuous support and all our research partners for the fruitful cooperation.

Enjoy reading the following pages!

95

LENSES FOR HARD X-RAYS WITH ULTRA-HIGH DIFFRACTION EFFICIENCY

B. Nöhammer, A. Dolocan, B. Haas, L. Heyderman, C. David (PSI), R. Widmer (IBM), M. Burghammer, C. Riekel (ESRF), H.P. Herzig (Uni Neuchâtel),

In order to increase the diffraction efficiency of diffractive x-ray optics we have developed a structuring process for the fabrication of blazed silicon Fresnel zone plates with staircase zone profiles. The efficiency of linear zone plates was measured using synchrotron radiation. We obtained values of up to 68 %for 12.4 keV photon energy, which is clearly beyond any value reported so far for diffractive x-ray optics.

Zone plates are important optical devices for x-ray optics and are useful in many types of set-ups where high flux density in a spot and high resolution imaging of an object is required. Up to now mostly binary zone plates (Rayleigh-Wood phase-reversal zone plates) are used, which have proved to give high resolution compared to refractive or reflective focusing optics, but normally have rather moderate diffraction efficiencies (typically between 10 and 20%). In order to increase the diffraction efficiency, we fabricated linear zone plates made of silicon, using a staircase (blazed) profile for the grating-structures (see Fig. 1), which can give diffraction efficiencies much higher than those of conventional binary zone plates.

The zone plates are defined using two accurately aligned electron-beam lithography steps resulting in a combined Cr/Al mask (see Fig. 1). The blazed structure profiles are formed by stepwise reactive ion etching of the silicon substrate and selectively removal of the Cr/Al mask layers [1]. The zone plates are fabricated on approximately 10 um thick silicon membranes formed by photo lithography and reactive ion etching to provide sufficient transmission for

a) Fabrication of AI/Cr-mask using e-beam lithography

M Cr

Si

b) RIE- of Si; dry-etching of Cr not protected by Al

c)RŒof Si; wet-etching of Al

d) RIE of Si; removal of residual Cr

L

hard x-rays. We were able to achieve a good approximation of the optimal grating profile for 1.5 urn structure height and grating periods down to 800 nm (see Fig. 1). Thus, the diffraction hmited spatial resolution of our lenses is limited by the smallest structure period to about 500 nm.

Fig. 2 : SEM-picture of a blazed linear zone plate giving ultra-high diffraction efficiency.

Our blazed zone plates were tested at beamline ID 13 of the European Synchrotron Radiation Facility (ESRF), Grenoble. The zone plates were tilted with respect to the x-ray beam to increase the effective structure height [2]. Using x-rays with 12.4 keV photon energy we were able to obtain diffraction efficiencies of up to 68 % which is higher than any value reported so far for x-ray zone plates.

Due to the demanding structuring process, the obtainable resolution is not as good as for zone plates with binary structures. The excellent efficiency of our blazed zone plates makes them suited for applications where high flux rather than ultimate resolution is required. This issue is of special importance when two orthogonal linear zone plates are used in series as in the case of coherence-matched microfocusing (see C. David et al., this annual report).

This work was funded by the Swiss National Science Foundation under contract No. 21-57085.99

Fig. 1: Fabrication process of blazed Fresnel zone plates and SEM-picture of the resulting structures.

REFERENCES

[1] C. David, Microelectronic Engineering 53, 677 (2000).

[2] C. David, B. Nöhammer, E. Ziegler, Applied Physics Letters 79, 1088 (2001).

96

COHERENCE MATCHED MICROFOCUSING OF HARD X-RAYS

C. David, B. Nöhammer, A. Dolocan, B. Haas, A. Grubelnik (PSI), M. Burghammer, C. Riekel (ESRF)

We developed a novel arrangement of two linear Fresnel lenses for the focusing of hard x-rays. By appropriately choosing the lens geometries, the aperture of the device can be matched to the coherently illuminated area of a specific x-ray source, which results in an increased flux density in the focal spot. Such a set-up was tested at the European Synchrotron Radiation Facility (ESRF), the gain influx density was found to be 105 for 12.4 keV photons.

A Fresnel zone plate (like all lenses) has to be coherently illuminated in order to give diffraction limited resolution. Usually the spatial coherence of synchrotron sources is very different in the horizontal and vertical directions due to the asymmetry of the source size. The shape of a coherently illuminated area is therefore elongated and not matched to a lens with a round aperture. If a round lens is small enough to be completely illuminated with coherent light, only a small fraction of the coherent photons are collected. On the other hand, if the lens is made large enough to collect all coherent photons, a diffraction limited focusing is possible only in one direction.

Fig. 1: Coherence matched focusing by two linear lenses. All coherent photons can be collected.

To match a microfocusing optic to the spatial coherence of an asymmetrical source, the horizontal and vertical focusing has to be performed by two separated linear lenses (see Fig. 1). In this case, all coherent photons can be focused into a diffraction limited, symmetrical spot. The ratio of the focal lengths should be identical to the source asymmetry b/a, i.e. the ratio of the source sizes in the horizontal and vertical directions. The gain in flux compared to a coherently illuminated round lens (i.e. with a maximum diameter of a) is also in the order of b/a, for a typical undulator beam line it usually is in the range of 4 to 10. However, in the case of focusing with Fresnel zone plates, the presence of a second lens in the beam results in additional losses due to the limited diffraction efficiency.

Recently, we developed a method for the fabrication of linear zone plates by wet chemical etching <110> oriented silicon substrates (see Fig. 2 top). By tilting the lenses with respect to the x-ray beam (see Fig. 2 below) the effective height of the diffracting structures can be significantly increased making the lenses suited for focusing of hard x-rays [1]. We tested a combination of two such lenses with 100 nm outermost zone width on beamline ID 13 of the ESRF. To match the dimensions of the x-ray undulator source at 12.4 keV photon energy, the focal lengths of the vertically and the horizontally focusing lens were chosen to

Fig. 2: Linear Fresnel zone plate with 100 nm outermost zone width made by wet chemical etching of <110> oriented silicon (top). The effective structure height of a linear zone plate can be increased by tilting with respect to the x-ray beam (below).

be 200 mm and 50 mm repectively. By scanning a test object with electroplated gold structures, we were able to determine the spatial resolution of the setup. Although the absorption of the test structures was only in the order of 6%, we were able to resolve structures down to 200 nm in both scanning directions. The fact that this value does not match the expected resolving power of around 100 nm is probably due to mechanical instabilities of the set-up.

The efficiency of each of the two lenses was measured to be 24%, meaning that the complete set-up has a diffraction efficiency of just below 6%. Due to good match to the beamlines coherence properties, a flux of around 109

photons per second was achieved. This corresponds to a flux density in the order of 10 1 0 phot/sec/um2, which corresponds to a gain of 105 compared to the incoming flux density of the beam line. Future work will focus on the implementation of blazed Fresnel lenses with greatly improved efficiency (see B. Nöhammer et al., this annual report) into the coherence-matched focusing scheme.

REFERENCE

[1] C. David, B. Nöhammer, E. Ziegler, Appl. Phys. Lett. 79,1088 (2001).

97

A SHEARING INTERFEROMETER FOR HARD X-RAYS

C. David, B. Nöhammer, H H. Solak, A. Dolocan, B. Haas (PSI), R. Widmer (IBM), E. Ziegler (ESRF)

A novel type of x-ray interferometer has been developed. We used two phase gratings and a Bragg-crystal to analyze the wave front distortions of hard x-rays. The resulting Moiré-pattern reveals the local amount of the phase shift between two wave fronts. The method has potential application for the characterization of x-ray optics or for phase imaging in micro-radiography.

The improved quality of modern synchrotron sources has led to a greatly increased coherence of the produced x-rays. On one hand this opens up the possibility to perform a large number of completely new scientific experiments. On the other hand the problem to maintain the quality of the generated radiation throughout all optical components of a beam line arises. The most sensitive method to measure the distortion of a wave front relies on the use of interfero­meters. A set-up for a Mach-Zehnder type interferometer for hard x-rays was introduced by Bonse and Hart [1]. It consists of three partially transmitting Bragg crystals used as beam splitter and recombining elements. The main technical difficulty of the Bonse-Hart set-up lies in the extreme demands with respect to the mechanical stability of the optical components.

We have developed a different kind of set-up, which is known from visible light optics as shearing interferometer. Here, the incoming plane light wave is not split into two completely separated branches but merely sheared by a small angle. For this purpose we fabricated Silicon diffractive optics with high aspect ratio structures by electron-beam lithography and wet chemical etching [2].

incoming x-rays

Fig. 1: Schematic view of the shearing interferometer set­up consisting of two gratings and a Bragg-crystal.

We tested this interferometer on the Optics beam-line of the ESRF for several photon energies between 12.4 and 24.8 keV. The basic set-up is depicted in Fig. 1. The first grating splits the incoming wave into the +l s t and - I s ' diffraction orders. The interference of these two wave-fronts results in a pattern of interference lines, which is analyzed by the second diffraction grating. The relative phase of the two beams determines how the incoming intensity will be distributed over the analyzer's diffraction orders. We used a Bragg crystal to separate the zeroth diffraction order. By a slight angular misalignment of the two gratings one obtains an interferogram of Moiré-lines. Distortions of the incoming wave front will result in a deformation of this Moiré-pattern. We plan to use this effect to map out the

Fig. 2: Shearing interferograms of 100 and 200 |tm poly­styrene spheres taken at 12.4 keV photon energy. Experimental results (a, b) and simulations (c).

quality of optical components such as mirrors situated upstream of the interferometer.

Another interesting application is the imaging of phase objects. We used 100 and 200 |tm diameter polystyrene spheres as well defined phase objects to investigate this effect (see Fig. 2). A change of the orientation of the Moiré-lines is observed, which is directly linked to the difference in phase of the two interfering beams. The obtained interferograms are in excellent agreement with numerical simulations. This shows, that a reconstruction of unknown phase objects from such images should be possible. In the hard x-ray region, the phase shift cross sections of light elements are much larger than the absorption cross sections. Thus, the contrast of x-ray micrographs taken in amplitude contrast is very low. The developed technique might therefore be suited to visualize an object with enhanced contrast. This would make it possible to reduce the applied doses in x-ray micro­radiography.

R E F E R E N C E

[1] U. Bonse, M. Hart, Appl. Phys. Lett. 6,155 (1965).

[2] C. David, B. Nöhammer, E. Ziegler, Appl. Phys. Lett. 79,1088 (2001).

98

MULTIPLE BEAM INTERFERENCE LITHOGRAPHY IN THE EUV AND VISIBLE REGIONS

H. H. Solak, C. David, J. Gobrecht (PSI), F. Cerrina, L. Wang (Univ. of Wisconsin-Madison)

Two-dimensional periodic structures over large areas are obtained by recording the interference pattern of three or more mutually coherent beams. The created patterns have potential applications in production of photonic crystals, magnetic dot arrays, and templates for guided self-assembly of nano-particles and macromolecules to name a few. The technique offers high contrast images, different pattern symmetries, and insensitivity to misalignment

Interference lithography is widely used to produce periodic patterns over large areas. In most applications interference fringes of two mutually coherent beams are recorded to obtain one-dimensional grating patterns. For applications that require two-dimensional periodic patterns interference lithography offers alternative routes. In the multiple-exposure scheme the substrate is exposed a number of times with two-beam interference patterns to obtain two-dimensional structures. For example, the substrate can be rotated by 90° between two exposures to record a square array of holes. Alternatively multiple beams can be used to form a two-dimensional pattern in a single exposure. The latter technique yields images with higher contrast with concomitant increase in process latitude.

We have developed an interference lithography scheme based on transmission diffraction gratings'. The method is schematically illustrated in Figure 1. A spatially coherent beam is diffracted by linear gratings symmetrically placed on a transparent substrate. The diffracted beams form a two-dimensional interference pattern in the central region where a photoresist-coated sample is placed for recording the pattern.

Fig. 1: Schematic of multiple-wave interference lithography. Sizes of gratings and the distances are chosen to avoid interference by undesired diffraction orders.

The contrast and shape of the image depends in general on relative intensity, phase and polarization of the interfering beams. In particular when the number of beams is four or more, the relative phase between the beams drastically affects the intensity profile. This sensitivity on phase directly translates into similar requirements on alignment of the interfering beams. Our approach based on transmission diffraction gratings overcomes these difficulties related to the phase control and alignment of the interfering beams. The diffracted beams from the gratings possess certain

phase relations, dictated by the relative positions of the gratings on the substrate. The required phase relation between the beams is hard-coded in the electron beam created pattern. In addition the system is insensitive to static misalignments.

We have performed experiments in the visible and EUV ranges demonstrating the feasibility of the method. Diffrac­tion gratings on quartz plates and Si 3N 4 membranes were used for the two wavelength regions respectively. In both cases gratings were written with electron beam lithography and etched into Cr films. Figures 2(a) and (b) show examples of square arrays of holes in photoresist obtained with this technique. The gratings were designed so as to yield the maximum image contrast in both cases.

• •H IHI i l l l l l ^ ^ ^ M C l l

Fig. 2: SEM micrographs of square arrays of holes obtained with four-beam interference lithography. (a) 1.77 um period array with 442 nm laser light. (b) 141 nm period array with 13 nm undulator radiation.

The EUV exposures were done on an undulator beamline at the Synchrotron Radiation Center of the University of Wisconsin. The short wavelength of the EUV radiation offers the possibility of going to extremely small periodicities, down to 10-20nm range. Periodic patterns with such high resolution are currently not available from existing lithography technologies in useful quantities. Therefore a project is currently underway to build an X-ray Interference Lithography (XIL) system at the Swiss Light Source (SLS). This project takes advantage of the unique coherence properties of the SLS, which provides fully coherent radiation up to about 100 eV photon energy.

REFERENCE

[1] H. H. Solak, C. David, J. Gobrecht, L. Wang, F. Cerrina, Micro- and Nano-Engineering MNE 2001, Grenoble, 16-19 September (2001).

99

NANO-STRUCTURED AR-SURFACES REPLICATED BY HOT EMBOSSING

C. David, E. Deckardt, D. Bächle (PSI), M. Schnieper, J. Söchtig, C. Zschokke (CSEM-Z)

We developed a fabrication technique of anti-reflective structures for applications in the visible and UV spectral range. We used electron-beam lithography and electroforming to produce a Ni stamper for the hot embossing into polycarbonate (PC) sheets. Optical measurements on the replicated PC gratings showed that the reflectivity has been reduced significantly.

Light reflection from surfaces such as lenses, displays or computer monitors, can significantly deteriorate the optical performance of a device by causing stray light or by degrading the transmission of optical components. Anti-reflective (AR) surfaces are therefore widely used. They mostly consist of vacuum-deposited coatings of dielectric material layers. The reflectivity of such a surface is zero, when the waves reflected from the two interfaces (substrate-coating and coating-surrounding medium) cancel out, i.e. they have equal amplitude and a half-wavelength phase shift (see Fig. la).

As an alternative, the same effect can be achieved by

a) dielectric AR-coating

A

b) sub-wavelength AR-grating

1.) E-beam exposure and development

4.) Ag metallisation and Ni electrofoiming

l.) Cr reactive ion etch and resist ashing

5.) PC hot embossing

3.) Quartz reactive ion etching and Cr removal

6.) Replicated AR grating

Fig. 1: Schematic view of a conventional AR-coating (a) and a nano-structured AR-surface (b).

patterning the surface with a grating pattern. When the period A of the grating is smaller than the wavelength, the incident light is not diffracted in a classical sense. The grating patterned layer rather acts as a layer with an effective refractive index n e f f with n 0 < n e f f< n2. By choosing appropriate values for the grating depth d and the line width, the conditions for suppressed reflectivity can be fulfilled. Compared to conventional dielectric coatings, anti-reflective (AR) gratings have a number of potential advantages, depending on the specific application: (i) AR gratings can cover a wide wavelength range with a single surface pattern, (ii) The surface relief can be replicated into polymers by fast, low-cost mass production techniques such as injection moulding or hot embossing, (iii) The principle of AR gratings also works for UV light, where the choice of dielectric coating materials with low absorption becomes very limited. Especially for intense, pulsed UV sources, AR gratings can withstand substantially higher fluences.

In this work, the second and third issue were addressed within a collaboration with the industrial partners Leica Geosystems and SwissOptic, Switzerland. We used elec­tron-beam lithography for the origination of various AR-gratings optimized for wavelengths around 550 nm and around 250 nm. The grating structures are transferred into a quartz master by reactive ion etching and then replicated into a nickel stamper by electroforming (see Fig. 2). This

Fig. 2: Pattern transfer process for the origination and replication of AR-gratings (top). Cross-sections of quartz masters with 160 and 120 nm period (below).

stamper is used for hot embossing into 1 mm thick polycar­bonate (PC) sheets at 150°C. Figure 2 shows an SEM image of the quartz master.

The reflectivities of DUV AR-surfaces were measured for both polarizations along (TE) and perpendicular (TM) to the grating lines. As an example, the obtained data for a grating with 120 nm period is shown in Fig. 3. Although the experimental curves only roughly match the theoretical calculations based on rigorous diffraction theory, a significant reduction compared to an unpatterned surface was obtained.

unpatterned surface

measured values TE polarization

measured values / »•••••••*•*

TM polarization •*•••*****

\ . . . • • - • • * * * * / ^ c ^ i ^ calculated values "calculated values T E polarization TM polarization

2 5 0 3 0 0 3 5 0 4 0 0 4 5 0 wave leng th [ nm]

5 0 0 5 5 0

Fig. 3: Calculated and measured reflectivities of a AR surface with 120 nm period.

FUNDING: KTI (SEGOEM), TOP NAN021 (NODE 1).

100

REAL-TIME OBSERVATION OF ELECTROMIGRATION INDUCED STRAIN IN INTERCONNECT LINES WITH IMAGING X-RAY TOPOGRAPHY

H. H. Solak, C. David, J. Gobrecht (PSI), M. Drakopoulos (ESRF, France)

Al interconnect lines suffer from reliability problems due to the often coupled electromigration and mechanical stress phenomena. We have developed a new technique - Imaging X-ray Topography - to study the evolution of strain in interconnects during the electromigration process. High spatial resolution x-ray topograms were obtained using in house developed diffractive x-ray optics as imaging elements.

Mechanical stress related failure of metal interconnect lines in integrated circuits is an important reliability problem. The electromigration process - movement of conductor atoms due to high-density electrical currents - influences the stress in metal lines. Electromigration causes stress changes by accumulating atoms in certain regions, and depleting them in others. However there have been very few verifying experimental measurements due to the difficulties of stress measurement with the required (1-10 um) spatial resolution 1 2 . X-rays with sufficient brightness form modern synchrotron sources and high-resolution x-ray optics have now made these measurements possible.

Strained '' Lattice

CCD \ Detector hv %

Fig. 1: Si (400) Bragg reflected x-rays from the sample are imaged onto a detector surface by an FZP lens. A high density electrical current passes through the metal Une, which is held at 250-275°C.

X-ray topography is a technique where imperfections in a crystal lattice - such as dislocations and strain fields - are observed as changes in the intensity of Bragg reflected x-rays. Normally the area of interest is illuminated with x-rays and a detector is placed in close proximity to the sample to record the "topography" of the lattice planes. In conventional x-ray topography, the finite distance between the sample and detector limits the resolution. Our imaging technique overcomes this problem since a real image of the intensity distribution on the sample surface is formed on the detector surface by the x-ray lens.

The samples consisted of Al lines patterned on Si (100) wafers. 8 keV monochromatic x-rays from the undulator beamline ID22 at the ESRF were incident on the sample as illustrated in Figure 1. The sample was aligned for the (400) Bragg reflection from the substrate. A Fresnel Zone Plate (FZP) is placed in the Bragg reflected beam, which forms a magnified image of the sample in the detector

Fig. 1: Evolution of stress in an Al interconnect line due to electromigration. The strain migrates up­wards towards the anode end. The two bright round areas are due to the strong stress created by tungsten contacts.

plane. A high-density electrical current is passed through the sample line, which is held at an elevated temperature by integrated heaters on the Si chip. The strain due to the electromigration process influences the underlying substra­te lattice. These distortions were imaged over a period of several hours to follow the evolution of the process. The FZP had zones as fine as 80 nm wide etched into a Ge film providing ample spatial resolution potential3.

Figure 2 shows three images of a 50 um long 2 um wide Une obtained at three distinct stages of the electromigration process. The first image was acquired after electron flow in the top to bottom direction has already created a strain concentration near the lower half of the Une. The following two images show the same sample after the current flow direction was reversed. After the reversal the strained area moved gradually upwards as seen in the second and third images respectively. A detailed analysis of the data is currently underway. We beUeve this is the first time the electromigration induced stress evolution has been observed in real time with a full field imaging technique.

The staff of LMN is gratefully acknowledged for their help in the preparation of samples.

REFERENCES

[1] I. A. Blech, J. Appl. Phys. 47, 1203 (1976).

[2] H. H. Solak, Y. Vladimirsky, F. Cerrina, B. Lai, W. Yun, Z. Cai, P. Ilinski, D. Legnini, W. Rodrigues, J. Appl. Phys. 86, 884 (1999).

[3] C. David, B. KauUch, R. Barett, M. Salome, J. Susini, Appl. Phys. Lett. 77, 3851 (2000).

101

DEVELOPING A TOOLBOX FOR NANO-REPLICATION

H. Schift, D.Bächle, E. Deckardt, J. Gobrecht, L.J. Heyderman, (PSI), M. Gale, J. Söchtig (CSEM), W. Raupach, D. Simoneta (FHAargau), M. Gabriel, J. Krummenacher (AWM), T. Hessler, C. Leister, (Leister), J.-F. Moser,

W. Tompkin (OVD), T. Callenbach, K. Eggmann (Weidmann)

Replication is a key technology for the fabrication of nano structured surfaces. It combines very high resolution capability with low-cost, mass production potential. NanoRep is an alliance project intended to create a technology base for nanoreplication in Switzerland by combining compentences of research institutes and industrial partners.

During the last few years, research institutes and industry in Switzerland developed a considerable number of tools for nanoreplication. Some of the processes have reached maturity, and consequently can be directly used for industrial applications. However, many of them have not yet proved stable nanostructuring ability or need further improvements. Our aim is to develop replication for use as a fabrication process of nanostructured components for research and industrial applications. For this we need a technology toolbox compromising technology (master fabrication, replication, pattern transfer), analytical tools, and professional process equipment.

hot e m b o s s i n g i n j ec t i on m o l d i n g

f S

mm. • stamp with surface relief

UV c a s t i n g

mmf

!:<lîli

IT pWIM ro l l e m b o s s i n g |

Fig. 1: Nanoreplication processes used by the partners in the NanoRep alliance.

Within the framework of TOPNano21, a network of partners in research and industry has the aim to complete the toolbox and make a comparative characterization of different replication technologies. The academic partners will carry out advanced R&D and the results will be made available to Swiss industry and to other TOP NANO 21 projects. This will have a major impact in enabling prototype nanostructured elements and devices to be fabricated and replicated. The industry partners will contribute with their extensive knowledge in tool fabrication, polymer processing and post-processing. They will gain experience in production technology for nanostructured surfaces, which will help them move into this field and produce products based on this technology.

PSI and CSEM have fabricated mold inserts for all the replication technologies of the project partners. The master

contained structures with lateral sizes down to 100 nm and aspect ratios of about 1. PSI was using electron beam exposure for structure definition. The original structures were then etched into a hard master and replicated by CSEM into Nickel shims by electroforming. The electro-forming technology enabled us to fabricate identical copies from the original stamps, but with a different shim thickness adapted to the requirements of every partner. Every partner was then using its own processes for the replication of the nanostructures. Finally the replication fidelity of the structures was measured and the results compared. The results can be summed up as follows:

• Every partner was able to perform replication tests with his own specific process using nanostructured stamps. Processes used were injection molding (AWM, WEIDMANN, FHA/KATZ), hot embossing (PSI, CSEM), UV casting (LEISTER, CSEM), roll embossing (OVD), see figure 1.

• The samples were measured with scanning probe techniques (measurement of surface profile) and optical methods (measurement of diffraction efficiency). All the replication processes used, although different in setup, materials, industrial scale and replication speed (throughput), show clear evidence that sub-um struc­tures can be replicated. Differences in replication fidelity became evident at structure sizes smaller than 200 nm but cannot yet been attributed to limits of the replication processes. Some processes showed that replication of sizes smaller than 100 nm was possible.

• Critical points in the process chain were identified and further progress can be expected by optimizing structure design, measurement procedures and by fine tuning of processes.

The NanoRep network is now continued (NanoRep2). The new project is scheduled from August 2001 to July 2002. With SPT ROTH (Lyss) a new industrial partner was included in the network, which allows us to add ceramic injection molding (CIM) to the replication methods used.

FUNDING: Swiss Priority Program TOP NAN021.

REFERENCE

[1] Annual report of TOP NAN021 meeting, Bern, October 16, (2001) (http://www.ethrat.ch/topnano21/).

102

CHEMICAL NANOPATTERNING USING HOT EMBOSSING LITHOGRAPHY

H. Schift, J. Gobrecht, L.J. Heyderman, C. Podeste, K. Vogelsang (PSI)

We demonstrate the patterning of silanes on silicon substrates using hot embossing and lift-off. Periodic structures with feature sizes < 500 nm have been replicated. We are expecting this method to be easily applicable for a range of different chemicals and for structure sizes down to 100 nm.

Nanoimprint technologies offer a variety of surface pat­terning possibilities and have been developed during the last few years to an impressive maturity. Hot embossing lithography (HEL) has proven its potential for structuring resists with high aspect ratios by thermoplastic molding and is an important fabrication process for topographic nano-structures down to a lateral resolution of some 10s of nm. The process is parallel and can be carried out with high throughput at a low cost.

Chemical surface coatings allow control over wettability, adhesion, chemical reactivity, electrical conduction, and mass transport to the underlying substrate. Silanes are often used for this task (silanisation), because they are covalently binding onto the surface. Self-assembled monolayers (SAMs) can be used as a resist-forming ink. Also func­tional biomolecules can be coated on artificial surfaces to be used for biosensors, for cell studies and tissue engi­neering applications. For many practical applications, pat­terned chemical surface coatings are needed [1].

pressure & heat stamp

thermoplastic film substrate

]~i n c opened window to substrate

-silane - thermoplastic film

structured silane layer

Fig. 1: Process scheme for achieving local chemical contrast using Hot Embossing Lithography, silane deposition and lift-off.

We developed a process with which chemical contrast can be obtained using hot embossing lithography and lift-off (Figure 1). First a thin thermoplastic film is coated onto a substrate and embossed. Then resist windows are opened by an oxygen plasma flash to remove the residual layer at the bottom of the embossed resist. A chemical coating is then applied from the gas phase or by immersion in a solution. The resist is dissolved away in acetone. As a result a chemical surface modification restricted to the areas of the resist openings is obtained. The wetting behavior was found to be different for the regions with different surface properties. Structures with urn-dimensions can be easily visualized using an optical microscope

(Figure 2). We are expecting this method to be easily appli­cable for a range of different chemicals and for structure sizes down to 100 nm.

20 \im

r f f f f

f f f f , f f

? r f r r f

r if t r •11

Fig. 2: Above: Micrograph of an embossed resist struc­ture (dark) on an oxidized silicon substrate (bright). Below: After chemical coating with a fluorinated silane and lift-off, the local difference in wetting behavior can be visualized by exposing the structure to humidity .

Hot embossing lithography provides a high resolution unmatched by other imprint methods. Silanes are available with various functional head groups. The process can be developed for the tailored topographical and/or chemical patterning of surfaces on the nanoscale. Diverse optical, electronic and mechanical devices can be fabricated this way.

REFERENCE

[1] H. Sorribas, C. Padeste L. Tiefenauer, Biomaterials 23, 893 (2002).

103

TRANSPORT OF NANOSPHERES IN FLUIDS

L.J. Heyderman, D. Bächle, F. Glaus, B. Ketterer, H. Schifi, C. David, J. Gobrecht (PSI), B.P. Cahill, A. Stemmer (ETHZ)

The transport of latex nanospheres by application of four-phase travelling-wave signals in a spiral electrode has been investigated. The electrodes were manufactured by electron beam writing and lift-off. Careful electrode design and mixture of aqueous suspensions resulted in the desired electric field induced motion of the nanospheres.

The controlled displacement of sub-um sized dielectric particles is of growing interest for the development of lab-on-a-chip applications for transportation, intermixing and separation. The transport of particles can be achieved using dielectrophoresis, which is the motion of dielectric particles in dielectric media due to polarisation by a non-uniform alternating electric field. In the present study, we have investigated the transport of latex nanospheres above a spiral electrode on application of travelling wave signals. The electrode design (avoiding areas of charge concen­tration and using materials resistant to the dielectric fluid), electric field (size, frequency and waveform), the particle surface conductivity and radius, and the conductivity of dielectric medium must be carefully chosen to control the motion of the particles.

Fig. 1: Four-electrode spiral structure.

Electrode structures including four neighbouring spiral electrodes with 750 nm linewidth and 750 nm gaps between electrodes were fabricated (Figure 1). First, the spiral electrode design was exposed in a 150 nm thick layer of PMMA on a silicon substrate with a S i 0 2 insulating layer using a LEICA LION LV1 electron beam writer. This machine is equipped with continuous path control allowing structuring of large areas without stitching errors. Lines of various widths are added using a defocused exposure. The exposed areas were then transferred into an evaporated 10 nm titanium/70 nm aluminium layer using lift-off. The thin layer of titanium provided good adhesion of the aluminium to the substrate. Electrodes have also been produced using hot embossing lithography and in combination with electroplating, it is possible to provide

large volumes of Nickel electrodes which are thicker and have narrower interelectrode gaps.

A channel was formed between the chip and a microscope cover slip using a spacer. A suspension of 500 nm latex spheres in pure water was introduced into the cavity by means of capillary forces. A four-phase voltage supply was used to apply high frequency travelling wave signals to the electrodes. The voltage applied to each electrode is 90° phase shifted to that applied to a neighbouring electrode.

Between 10 kHz and 1 MHz, radial movement of spheres towards the centre or edge of the spiral was observed. The spheres travelled in the same direction as the travelling wave. In Figure 2, the particles move towards the center from both the bottom and top halves of the spiral. The motion of two of the spheres is indicated by arrows.

Fig. 2: Series of frames showing the transport of latex nanospheres to the centre of the spiral on applying a 1 MHz signal.

Our initial motivation was to transport the particles by means of travelling-wave dielectrophoresis. However, the observed effects justify further investigation.

FUNDING: ETHZ Polyproject NANO II, PSI

REFERENCES

[1] L.J. Heyderman, H. Schift, C. David, B. Ketterer, M. Auf der Maur, J. Gobrecht, Microelectronic Engineering, 54,229 (2000).

[2] D. C. Politano, P. V. Prati, S. J. Woo, O. J. Homan, F. M. Moesner, A. Stemmer, Dielectrophoretic Handling of Mesoscopic Objects, Proc. 4th Conf. on Motion and Vibration Control, 1139 (1998).

104

PHOTOLUMINESCENCE AND RESONANT TUNNELING OF Si/SiGe QUANTUM WELLS GROWN ON RELAXED 50%/50% SiGe VIRTUAL SUBSTRATE

H. Sigg, L. Diehl, S. Mentese, D. Grützmacher, E. Müller, S. Stutz, PSI, U. Gennser, (LPN-CNRS, F), D. Bensahel (STMicroelectronics, F), J. Faist (University of Neuchâtel)

Layer homogeneity and interface interdiffusion under annealing at T <650 C is studied by photoluminescence from quantum layers of, respectively, SilxGex with x = 0.8 and Si grown on a relaxed buffer. The appearance of resonant tunnelling in double barrier diodes is evidence for the high quality of interfaces and Si barrier layers.

For the successful development of a Si based quantum cascade laser, various spectroscopy tools are required to characterise the quality of the grown SiGe layers and their interfaces. Layer thickness and composition can for example be investigated by photoluminescence (PL). This technique has the added advantage that in the case of symmetrically strained Si/SiGe quantum wells (QW's) -the building block for the future cascade structures -information on the confinement in both the Si and SiGe layers is obtained (type II band alignment). Here PL investigations are discussed together with vertical transport studies of double barrier structures.

Samples for this study have been grown by MBE under the same condition as is currently used for cascade struc­tures. Low growth rate at T ~350 °C is applied to prevent the formation of Ge islands and misfit dislocations. The substrate consists of a step graded relaxed buffer which has been flattend by chemical mechanical polishing. Substrates have been grown by CVD at STMicro­electronics.

The PL is measured at T~2 K using laser excitation at 488 nm wavelength. The PL light has been collected by a f/1.5 optic and has been analyzed and detected by a Fourier transform spectrometer and InSb photodiode cooled to LN2 temperatures, respectively. A strong PL peak is observed at energies between 0.5 eV (for a Si/SiGe sample of 18Â/35Â thicknesses) to 0.65 eV (10Â/25Â). Red-shifted by an energy of ~55 meV, the phonon energy in

e 4

S 2

0

0.4

T = 2 K

Position (mm)

- H O W : S/SiSs 10A/25À

- H 0 4 2 : Si/SiGe 15Â/25Â

gap reqombination

0.5 0.9

Fig. 1:

0.6 0.7 0.8

Energy (eV)

PL spectra of Si/SiGe taken at T = 2 K. The band-line up of the conduction band (at the A point in k-space) and the heavy hole (HH) valence band (at the T-point) is shown in the inset, left hand side. The energy vs position on the sample is given in the inset, right hand side.

strained Si, a second but weaker replica is observed. This phonon replica, together with the confinement shift identifies the PL as the spatially indirect recombination of electrons and holes confined in the adjacent Si/SiGe layers. As the transition energy is considerably lower than the bandgaps in the strained Si and SiGe, these measure­ments provide the immediate evidence for type II band-alignment. The PL feature at 0.8 eV is independent of the QW layer thickness and is related to defects, probably misfit dislocations.

The observed PL energy shift of 2.5 meV over 1 cm (ra­dially, from the centre of the wafer, see inset Fig.1) corresponds to a variation in the molecular flux of approximately 0.3 %. Since changes in the Ge flux lead to both, (strain induced) bandgap variations as well as confinement shifts, the PL energy depends largely on the Ge deposition rate. From PL performed on samples isochronally annealed for 5 min, the temperature for which interdiffusion sets in is found to be between 600 and 650 °C. But, as expected for strain symmetrized structures, the linewidth of the (slightly shifted) PL is not increased be­cause no defects are introduced yet at these temperatures.

0 A 100 ri 11111111111111111111111111111111111111111111111111111111111

-1.50 -1.25 -1.00 -0.75 -0.50 -0.25 0.25 0.50 0.75 1.00 1.25

Vo l tage [V]

Fig. 2: Tunneling current vs. voltage for an asymmetric double barrier structure. The inset depicts the energy diagram.

Vertical transport studies through double barrier structures (DBS) are undertaken to study the injection properties from HH and LH states. Initial experiments on DBS with Si barriers and a strained SiGe injector show well resolved transmission resonances. The asymmetry in the I-V (Fig.2) reflects the asymmetric injector configuration.

FUNDING: PSI, SNF

105

INTERSUBBAND ABSORPTION MEASUREMENTS PERFORMED ON P-TYPE Si/Si 0 2 Ge 0 8 QUANTUM WELLS GROWN ON Si 0 5 Ge 0 5 VIRTUAL SUBSTRATES.

L. Diehl, H.Sigg, G. Dehlinger, D. Grützmacher, E. Müller, S. Stutz, B. Haas (PSI), T. Fromherz (Univ. Linz), U. Gennser, I. Sagnes (CNRS), D. Bensahel, (STMicroelectwnics), J. Faist (Univ. Neuchâtel)

Intersubband absorption measurements on modulation doped Si/Si02Ge0S quantum wells, grown on Si05Ge05 virtual substrate, have been performed up to room temperature. Several resonances are observed experimentally and identified using a 6 band k p model. The well-resolved absorption signals indicate the suitability of virtual substrates for the realization of a Si/SiGe QC laser.

Quantum cascade lasers (QCLs) have attracted an in­creasing attention since the first experimental demonstra­tion in 1994 because of their potential applications, e.g. for molecular spectroscopy. The III-V material sytem, typically InGaAs/InAlAs, is the material of choice for the realization of QCls. Among the other possible combination of materials, Si/SiGe based structures are of particular interest, because of their possible compatibility with the well-established CMOS-technology.

Recently, we have reported. (Ref. 1) on intersubband electroluminescence in the 9 um range from p-type Si/SiGe cascaded structures grown by MBE pseudomorphically on Si (100) substrates. But improvements of the devices are drastically limited by the large strain present in the crystal. The use of SiGe pseudo-substrates is a way of circum­venting this problem, since alternating Si-and Ge-rich layers can result in a low net strain if the overall concentra­tion of Ge in the heterostructure and the one of the SiGe pseudo-substrate are matched. There is however a lack of knowledge concerning the growth of such heterostructures and some physical parameters, such as the bandoffsets.

Here we report on intersubband absorption measurements performed on modulation doped quantum wells grown by MBE on a Si/Si 0 5 Ge 0 5 pseudosubstrate. The samples are a repetition of four Si/Si 0 2 Ge 0 8 QWs, embedded in two 18 Á Si barriers. Ohmic contacts were fabricated by Al evapora­tion and a 900x900 urn2 Ti/Al Schottky gate is then evapo­rated. It is used to modulate the carrier population in the quantum wells and consequently the intersubband absorp­tion. It can therefore be discriminated from the non-modu­lated thermal background using lock-in technique.

Polarization dependent absorption measurements, obtained at 14K for a structure with 35 Â wide QWs, are displayed on Fig. la). Three peaks, which can be observed up to room temperature, are clearly distinguished at energies ranging from 250 to 550 meV. The result of a 6 band k*p model, also shown on Fig. lb), is in excellent agreement with the experimental data, and allows to make the following assignment for the different resonances. The strongest peak, a heavy hole to heavy hole transition, occurs in TM polarization only, according to the well-established polarization selection rules. The blue shift of this peak, as the QW width is decreased from 35 to 25 A, is well reproduced in our model. The energy of 325 meV obtained with the thinnest QW, corresponds to a wave­length of 3.8 urn, and is to our knowledge, the shortest

wavelength measured for a intersubband transition between HH states in the valence band of Si/SiGe heterostructures.

The features in the spectra, observed when the light is TE polarized, are due to a complex interplay between heavy, light and split-off states. The coupling of these resonances together with unconfined states, leads to interesting Fano interference effects. Despite the complexity of this situa­tion, our model can reproduce accurately the experimental data showing that the set of physical parameters used are well-determined.

H "

r* /

a) Simulation -6 band k-p model :

— TM polarization : — TE polarization

b) Exr je r j r r ie r i t ^ j jggu l te ~~

m kam ™

; T= 14 K :

/

150 200 280 300 3SÜ 400 450 SOD SSO 600

Energy [meV)

Fig. 1: Comparison between measurement and theoretical predictions for a sample with 35 A wide QW.

In summary, intersubband absorption measurements have been performed on Si/Si 0 2 Ge 0 8 modulation doped QWs grown by MBE on Si/Si 0 5 Ge 0 5 relaxed buffer layers. Transitions between HH and LH-SO states are observed up to room temperature. Bandstructure calculations are found to accurately predict details of the complicated energy level structure. The well-resolved absorption signals give an indication of the suitability of relaxed buffer layers for the realization of a Si/SiGe QC laser.

REFERENCE

[1] G. Dehlinger, L. Diehl, U. Gennser, H. Sigg, J. Faist, K. Ensslin, D.Grützmacher, E. Müller, Science 290, 2277 (2000).

106

THERMOPHOTOVOLTAICS - FROM DEVELOPMENT TOWARDS APPLICATION

B. Bitnar, W. Durisch, G. Palfinger, J.-C. Mayor, H. Sigg, D. Grützmacher, J. Gobrecht (PSI)

Thermophotovoltaics (TPV) - a technique for the conversion of heat into electricity by the use of photocells - can be applied for the development of an electrically self-powered domestic boiler. A small prototype TPV system was built and theoretically modelled to optimise the system design. With that knowledge a large demonstration system was fabricated, which will be mounted into a commercial domestic boiler.

Thermophotovoltaics (TPV) is a technique to convert heat into electricity by the use of a radiation emitter and photocells. An application of TPV is its integration into domestic boilers to generate the electrical power necessary for the operation of the boiler. In peripheral/mountainous regions TPV boilers can safeguard a very high heat supply security.

We built a small TPV prototype system, working with an Yb 2O s selective emitter and silicon solar cells (for details see [1]). This system produced 48 W electrical power with 2 kW thermal input power. The ratio of electricity to heat t| s y s was 2.4 %, a record value for silicon TPV systems.

This system was studied in detail and optimised by deve­loping a simulation model of the system. Fig. 1 shows the cylindrically symmetric model schematically. It includes the components emitter, filter, photocells and axial reflec­tors, whose optical spectra are used as input parameters for the simulation. The balance of the energy fluxes Q, is calculated numerically. Together with a combustion model, the electrical output power P e l can be calculated as a func­tion of the thermal input power Pth.

Fig . l : System model, for details see text.

Tab. 1 gives the result of the simulation of the prototype system. The good agreement with the experimental data (better 3 %) demonstrates the high quality of the simulation. Further simulations show, that removing one axial reflector reduces the output by 10%. The replacement of the used quartz filter by an infrared reflective Sn0 2 filter, which is still under development, should increase the output by around 10 %. The model also allows estimations of the maximum electricity to heat ratio achievable with the prototype system. Either by using a perfect filter (trans-mittance 100 % for convertible and reflectance 100 % for the remaining radiation), or by the use of a heat recuperator to preheat the combustion air with heat from the exhaust gas, an electricity to heat ratio of about 10 % should be achievable.

P,h [kW] T [K] em L J

P., [W] t U % ]

Sim. 1.96 1777 47 2.4

Exp. 1.96 - 48 2.4

Table 1: Results of simulation (Sim.) and experiment (Exp.), T e m is the calculated emitter temperature.

In a further step, a larger demonstration system was built, based on a 20 kW methane burner. This system was mounted into a commercial domestic heating boiler from HO VAL AG, Vaduz (FL), which is shown in Fig. 2.

Fig. 2 : TPV system mounted into a domestic heating boiler from HO VAL AG.

To be compatible with the existing boiler technology, no axial reflectors could be used and the module consists of relatively inexpensive solar cells, compared to the proto­type system. A detailed description of the system together with cost estimations for the electricity generated with this boiler, are given in [2]. During laboratory tests, the demon­stration system achieved 121 W electrical power at 12 kW thermal power, enough to run a boiler independently of the electricity grid. For the near future, detailed tests of the complete system are planned and the grid independent operation of the boiler will be demonstrated.

FUNDING: PSI, BFE.

REFERENCES

[1] W. Durisch, B. Bitnar, J.-C. Mayor, F. von Roth, H. Sigg, H. R. Tschudi, J. Gobrecht, 17th EPVSEC (2001), in print.

[2] G. Palfinger, B. Bitnar, W. Durisch, J.-C. Mayor, D. Grützmacher, J. Gobrecht, 17th EPVSEC (2001), in print.

107

TOWARDS SiGe LOW BANDGAP PHOTOCELLS GROWN BY UHV-CVD

G. Palfinger, B. Bitnar, H. Sigg, E. Müller, S. Stutz, D. Grützmacher (PSI), G. Willeke (FHG-ISE)

SiGe low bandgap photocells can for example increase the electricity output of a thermophotovoltaic system. For their development, the absorption of SiGe layers or dots have to be known. The absorption measurement by multiple internal reflection anda first result, indicating the extension of the absorption up to 1450 nm, is presented.

Thermophotovoltaics (TPV) is the conversion of heat into electricity by means of a radiation emitter and photocells. Ideally, the radiation spectrum of the emitter is matched to the photocells and the radiation power is maximized. Mono-crystalline silicon photocells absorb only light with a wavelength of less than about 1100 nm. At a typical emitter temperature of 2000 K, the maximum blackbody radiation density is at a wavelength of 1450 nm. Hence, TPV systems based on with a bandgap significantly lower than Si cells can achieve up to 3 times higher efficiencies than TPV systems based on mono-crystalline silicon cells, leading to a significant cost reduction of TPV generated electricity if the price of the low bandgap cells is in the same order of magnitude as that of mono-crystalline silicon cells [1]. The production of SiGe photocells can be expected inexpensive because they are processed on the base of the mainstream silicon technology.

In order to enhance the absorption of mono-crystalline silicon photocells towards longer wavelengths significantly, SiGe layers or dots with high germanium content should be put into the cell. As the strain causing lattice mismatch between silicon and germanium is about 4 %, only thin layers of SiGe on silicon can be grown epitaxially. The resulting critical layer thickness, the growth rates and the quality of the grown layers have been determined for our UHV-CVD reactor at 550 °C by analysing a series of samples with TEM and X-ray diffractometry. Fig. 1 shows a TEM picture of a stack of 10 Si/Si 0 f i f iGe 0, 4 layers.

20 nm

Fig. 1: TEM picture of 5.3 nm thick Si 0 6 6 Ge 0 3 4 layers (dark) with 5.4 nm thick Si buffer layers. Due to strain, the layers relax into a wavy structure.

One of the most important material parameters for the development of a photocell is its absorption. However, even figures for pure germanium varies by one order of magnitude between different sources found in literature. Data for bulk SiGe are even less accurate and the effects of confinement and strain are not taken into account. Therefore, a set-up has been developed to measure the

absorption of SiGe structures and to study the influence of confinement and strain on the absorption. As the grown layers are rather thin, the absorption of the SiGe layers is low, respectively. To get a measurable absorption, the light has to pass the layers multiple times. This is achieved by the set-up, which is schematically drawn in Fig. 2: The ray of light enters the sample via the 45° polished front, where it is refracted. Afterwards, it is 200 times internally totally reflected between the bottom and the top of our sample of the size 20 x 38 x 0.38 mm.

Fig. 2 : Top view (left) and side view (right) of a ray of light passing through the sample.

A first result of the absorption measurement is shown in Fig. 3. The transmission of a silicon sample with SiGe layers shown in Fig. 1 is compared with one without these layers. Clearly visible is that the absorption in the SiGe sample extends to a wavelength of 1450 nm.

100

wavelength X [nm]

Fig. 3 : First result of a measurement on a silicon (solid line) and a Si 0 6 6 Ge 0 3 4 (dotted line) sample.

REFERENCE

[1] G. Palfinger, B. Bitnar, W. Durisch, J. C. Mayor, D. Grützmacher, J. Gobrecht, „Cost Estimates of Electricity from a TPV Residential Heating System", Proc. 17* EPVSEC (2001), in print.

108

SELF ASSEMBLED VERTICAL SILICON QUANTUM WELLS FORMED BY THE GROWTH OF Si 0 8 Ge 0 J ON PATTERNED SUBSTRATES

A. Beyer, E. Müller, S. Stutz, H. Sigg, C. David, B. Ketterer, D. Grützmacher (PSI), K. Ensslin (ETHZ)

A new mechanism was found for the formation of nanometer sized structures in the silicon germanium material system. The growth ofSi0SGe02 on a special line shaped mesa pattern on a Si (001) surface leads to the formation of a vertical Si rich quantum well (VSQW). All investigated samples with a VSQW show the same adjacent facets. These were determined combining cross-sectional TEM and top view SEM images to (15 3 23) surfaces.

Quantum confinement effects are widely utilized, in order to improve the optical properties. The self assembling formation of nanometer sized structures is an attractive way for their creation. We have found a new self assembly mechanism for forming to form a VSQW in the Si Ge material system.

Fig. 1: Cross-sectional TEM image sequence from the SiGe with embedded quantum structures grown on the line shaped mesa patterned Si wafer.

The VSQW was found after the growth of S i 0 8 Ge 0 2 by MBE on a special line shaped mesa pattern. The pattern was created by e-beam lithography on Si (001) wafers. 2 nm deep and about 1.7 |0,m wide trenches were etched to define 300 nm wide line shaped mesas. The lines were aligned 15° off to the [100] direction. Si and Ge were deposited by e-beam evaporation using a substrate temperature of 620°C. First a 1.2 |Jm thick Si 0 8 Ge 0 2 step graded buffer layer was grown. On top of this buffer layer Ge islands have been deposited using 7 monolayers of pure Ge, followed by a 2.5 nm thick silicon layer and a 20 nm

thick Si 0 g Ge 0 2 spacer layer. These three growth steps were repeated 10 times.

Cross sectional TEM images from this sample are shown in Fig. 1. A vertical bright thin line through the center of the mesa structure is visible, indicating an enrichment of Si. This 17 nm thick VSQW was observed in two more samples, which were fabricated in the same way. All three samples show the same adjacent facets, indicating their importance. The angle between the two adjacent facets in the shown TEM images was determined to (112.6±0.3)°, by averaging ten measurements.

Fig. 2: SEM top view image from the structure shown in Fig. 1.

The SEM top view image in Fig. 2 reveals an additional information about the facets. In the centre appears a thin line, which is twisted to the mesa line of about 4°. This line is assigned to the top corner in Fig. 1. With these angels the facet was determined to the (15 3 23) surface. This surface was found to be very stable [1]. Moreover this facet is observed for Ge dome clusters [2]. Thus the formation of the VSQW is potentially driven by a reduction of the (15 3 23) surface energy due to a raise of the Ge content in this facet, i.e. the mean free path of Si adatoms on this surface appears to be larger than that for Ge.

FUNDING: SNF, PSI.

REFERENCE

[1] Zheng Gai, Xiaowei Li, R.G. Zhao, W.S. Yang, Phys. Rev. B 57, R15060 (1998).

[2] F.M. Ross, R.M. Tromp, M.C. Reuter, Sience286, 1931 (1999).

109

LOW TEMPERATURE GROWTH OF STRAIN COMPENSATED Si/SiGe QUANTUM WELLS ON RELAXED Si 0 5 Ge 0 5 BUFFER LAYERS

D. Grützmacher, G. Dehlinger, S. Mentese, E. Müller, S. Tsujino, T. Neiger (PSI), D. Bensahel (STMicroelectronics))

To achieve maximum freedom for the design of quantum cascade structures using intersubband transitions in the valence band of SiGe quantum wells, multiple quantum well and cascade structures with 80% of Ge in the wells have been deposited on relaxed Si05Ge05 buffer layers. Low temperature molecular beam epitaxy at T=300°C has proven to be a suitable technique to deposit structures of high structural perfection.

The aim of this study is to develop a growth sequence for Si/SiGe multiple quantum well and superlattice structures, which are suitable for the fabrication of Si based quantum cascade lasers. This device relies on intersubband transitions in the valence band of SiGe quantum wells Proper design is requested to align the subbands to injector and extractor states under bias conditions. Furthermore a large band offset between the SiGe well and the Si barrier is required to minimize thermal escape. Consequently SiGe quantum wells with high Ge concentration and pure Si barriers have to be deposited on relaxed SiGe buffer layers. In addition, the growth of Si under tensile and SiGe under compressive strain on relaxed buffer layers leads to a strain compensation allowing for huge numbers of quantum cascades. Moreover the relaxed buffer will improve the waveguide properties of the structure. Here we study the deposition of Si/SiGe multiple quantum well (MQW) and cascade (QC) structures with 80% Ge in the wells on relaxed buffer layers with a Ge concentration of 50%. The buffer layers were CVD grown and have been obtained from ST microelectronics in Grenoble. After the growth of the step graded buffer and prior to the deposition of the final Si 0 5 Ge 0 5 relaxed layer they have been polished to minimize surface roughness induced by stacked dislo­cations.

Fig. 1 shows cross sectional TEM micrographs of Si/Si 0 2 Ge 0 8 MQW's grown at 330°C on relaxed buffer layers. The structure shown in Fig. la contains Si 0 2 Ge 0 8

wells sandwiched between 1.8 nm wide Si layers and separated by 30 nm wide Si 0 5 Ge 0 5 spacer layers. The second sample (Fig. lb) contains a Si/ S i 0 2 Ge 0 8 MQW structure with 1.8 nm wide Si barriers and 2.5 nm wide wells grown under identical growth conditions.

Fig. 1: High resolution cross sectional TEM images of Si/SiGe MQW's grown on relaxed SiGe buffer layers at 330°C.

Whereas the MQW depicted in Fig. la has smooth and abrupt interfaces the MQW shown in Fig. 2a exhibits an increased waviness of the interfaces towards the top. Strain fields of small thickness or compositional fluctuations in the SiGe wells, which induce islanding in the consecutive layers and consequently amplify themselves, can explain this effect.

Fig. 2: a) High resolution TEM images and b) reciprocal space map at the 224 reflex of a 3 period Si/SiGe cascade structure grown on a relaxed SiGe buffer layers at 300°C.

A further reduction in temperature reduces the surface mobility of ad-atoms and decreases the tendency of islanding in SiGe layers with high concentrations. The 3 period Si/Si 0 2 Ge o s cascade structure shown in the TEM of Fig 2a was grown at 300°C. Abrupt interfaces are observed throughout the complete stacks of layers. The structural perfection is reflected in the x-ray data. Fig. 2b shows a reciprocal space map at the 224 reflex showing a large number of high order diffraction peaks. They line up with the buffer layer peak, indicating the strain symmetry in the structure. X-ray diffraction measurements were also performed at the 004 reflex. Excellent agreement was obtained between the measured rocking curve and a simulation assuming the design parameters for thickness and compositions of the individual layers. The results prove excellent control of various complex SiGe quantum well and cacscade structures, required for the successful development of a Si based quantum cascade laser.

REFERENCE

[1] G. Dehlinger, L. Diehl, U. Gennser, H. Sigg, J. Faist, K. Ensslin, D.Grützmacher, E. Müller, Science 290, 2277 (2000).

110

SHAPE TRANSFORMATION OF Ge CLUSTERS ON Si (100) SUBSTRATES

O. Kirfel, E. Müller, D. Grützmacher (PSI), K. Kern (EPFL)

The shape and composition of Ge clusters on Si do not only depend on the conditions during the formation of the clusters itself. The overgrowth of Ge clusters with Si to embed the Ge clusters in a Si crystal can lead to shape and composition changes. As the electronic properties depend on those physical values, we have investigated the changes by Scanning tunneling microscopy.

The deposition and formation of Ge clusters on Si surfaces are of high interest for opto-electronic applications, as theoretical model calculations show, that the reduction in size of the clusters down to ~10nm might lead to an increase of the radiative recombination processes [1]. The experiments have shown, that the necessary overgrowth of Ge dots with a Si layer to embed them in the Si crystal, can lead to changes in shape and composition of clusters, affecting the radiative recombination probability.

We have investigated the shape of the Ge clusters with a Scanning Tunneling Microscope (STM) prior and after the overgrowth with Si. Here we present two samples. Both contain Ge islands grown at 620°C from 6.5ML of Ge deposited on a lOOnm thick Si buffer layer grown at 750°C. Whereas the fist sample contains no Si cap layer, 5ML of Si was deposited at 620°C on top of the islands in the second sample.

(105)

{15 3 23}

{1 1 3}

{105}

Fig. 1: Empty state image (+3.0V, 272pA) of Ge clusters (6.5ML @ 620°C). Dome and hut clusters with typical facets are present.

The sample without a cap layer is grown in a regime, where dome and hut clusters exist simultaneously, as can be seen in figure 1. The dome clusters have {105}, {15 3 23} and {113} facets, which are frequently observed for Ge dome clusters [2]. The hut clusters have the typical {105} facets. The side lengths of the huts (30-60nm) and the diameters of the domes (48-68nm) are in a comparable range. Even though the base widths are comparable, the heights of the hut clusters (3.8-7.6nm) are by a factor of about two smaller than those of the domes (7.6-11.5nm).

A STM scan of the sample capped with 5ML of Si is shown in figure 2. Only hut clusters with the {105} facets are observed. This indicates a shape transformation from the initial uncapped dome clusters to final hut clusters due to the capping of the dome clusters with 5ML Si. The shape

transformation is reflected in the diameter and height distributions. The diameter range is shifted to higher values (45nm to 102nm), indicating a mass transport from the top of the initial dome clusters to the pedestals of the finally formed hut clusters resulting in larger bases for those clusters.

Fig. 2: Empty state image (+3.0V, 192pA) of Ge clusters (6.5ML @ 620°C) with a Si cap layer (5.0ML @ 620°C). Only hut clusters can be found.

The mass transport leads to a shrinking of the height of the initial dome clusters. A height range of 2.9-8.9nm is obtained, which are lower values than those of the uncapped domes (7.7-11.5nm).

To reveal the impact of the Si deposition on the initially uncapped hut clusters a more careful analysis of the data is required. The heights of the uncapped hut clusters are in the range of the capped clusters. As the diameter range of the capped hut clusters (48-103nm) starts at a higher value than those for the uncapped hut clusters (30-60nm), we believe that the Si of the capping layer intermixes with the initial uncapped hut clusters. Since the {105} facet is shallow this increase in size leads to a more pronounced increase in diameter than in height of the islands.

Both, the shape transformation which results in higher aspect ratios and the intermixing of clusters with Si are bothering for opto-electronic devices. Therefore growth techniques have to be developed, which can suppress these phenomena.

REFERENCE

[1] B. Delley, E. F. Steigmeier, Phys. Rev. B 47 (3), 1397 (1993).

[2] F. M. Ross, R. M. Tromp, M. C. Reuter, Science 286,1931 (1999).

1 1 1

LOW-TEMPERATURE OVERGROWTH OF Ge CLUSTERS ON Si(OOl) WITH PRESERVATION OF THEIR MORPHOLOGY

E. Müller, O. Kitfei, D. Grützmacher (PSI), A. Rastelli, H. von Känel (ETHZ)

Coherently strained Ge-clusters on Si(001 ) were overgrown with Si at temperatures between 300°C and 650°C. By transmission electron microscopy the clusters were found to strongly flatten and intermix at temperatures above about 450°C. By contrast, a good preservation of the original morphology as well as a recovery of aflat Si surface were achieved by low temperature capping at 300°C followed by Si growth at 550°C

In the Stranski-Krastanow growth mode Ge islands are formed on top of Si(OOl). The self-assembly of such islands offers a way to overcome the limitations of litho­graphy when growing zero-dimensional structures on a nanometer scale. For applications the islands have to be covered by at least some nanometers of silicon. Trans­mission electron microscopic images of capped SiGe clus­ters, however, illustrate the occurrence of drastic changes of their shapes due to Si overgrowth at temperatures typical for the epitaxial growth of Si/SiGe heterostructures.

o 20 nm

Fig. 1: Shape changes of Ge dome clusters upon Si overgrowth: high-resolution transmission electron microscopic images and elemental maps (Si-rich areas are bright), respectively, of Ge dome clusters without coverage (a, b), capped with 3 ML Si (c, d) and covered with 5 ML Si (e, f).

In [110] projection, Ge dome clusters grown at temperatures of 500 - 650°C (Fig. la) have contact angles to the Si substrate of 26° - 27°. This is in the range of angles expected for {113} and {15 3 23} facets [1,2]. According to elemental maps the Si-distribution within uncovered Ge islands is nearly uniform (Fig. lb). At a Si-coverage of 3 monolayers (ML) first indications of a shape change are visible (Fig lc). New facets with contact angles of typically 11° start growing at the pedestal of the islands. They can probably be attributed to a {117}-type facet. In the Si-map, the brighter contrast of the new shallow facet (arrowed) indicates a higher Si content compared to the rest of the island due to alloying (Fig. ld). After a Si-coverage of 5 ML the Ge islands have lost about half of their height and a (001) top facet has formed (Fig. le). Most contact angles are about 8°, indicating the presence of {105} facets known from Ge hut clusters. On the elemental map strong alloying can be recognised in those parts of the dots, which

have formed during Si-coverage, i.e. the shallow edges, while in the center a Ge-rich, dark core remains (Fig. If).

Sinces such shape changes have a measurable effect on physical properties [3,4] attempts were made to preserve the morphology. Again the Ge clusters were grown at temperatures of 500 - 650°C, but they were covered at lower temperatures in order to reduce the surface mobility of the atoms and therefore the intermixing of Si and Ge during growth (Fig. 2). At a temperature of 450°C first indications of a slightly reduced mophology change were found (Fig. 2b). But only at a temperature as low as 300°C a nearly full preservation of the shape of the Ge clusters was achieved. Continuing the Si-overgrowth at 300°C the Si-surface follows the profile of the Ge layer (Fig. 2c). In order to re-establish a flat Si surface (as it is needed e.g. for a next layer of Ge islands) the growth temperature was raised after a Si coverage of 30 nm from 300°C to the initial value of 550°C. After the growth of another 30 nm of Si a flat surface was established without appreciably changing the shape of the burried Ge-clusters (Fig. 2d).

Fig. 2: Ge dome clusters covered with Si at a temperature of a) T = 550°C, b) T = 450°C, c) T = 300°C, d) T = 300°C for the first 30 nm and T = 550°C for the second 30 nm of coverage, respectively.

REFERENCES

[1] F. M. Ross, R. M. Tromp, and M. C. Reuter, Science 286, 1931 (1999).

[2] Z. Gai, X. Li, R. G. Zhao and W. S. Yang, Phys. Rev. B 57, R15060 (1998).

[3] J. P. Liu, J. Z. Wang, D. D. Huang, J. P. Li, D Z. Sun, M. Y. Kong, J. Crystal Growth 207, 150 (1999).

[4] O. G. Schmidt, U. Denker, K. Eberl, O. Kienzle, F. Ernst, Appl. Phys. Lett. 74, 269 (1999).

112

ULTRATHIN NANOPORE MEMBRANES FOR BIOANALYSIS

L. Tiefenauer, B. Ketterer, B. Haas, K. Vogelsang, L. Heyderman, (PSI), O. Dubochet (Leister Process Technol.)

The aim of this feasibility study is to explore the technology for the fabrication of thin membranes with pores below 100 nm diameters. The key process is the transfer of nanodots patterns to PMMA resist by the hot embossing technique. The resulting nanochips can be used for many bioanalytical applications.

Protein assemblies in biological bilayer membranes are in a size range of 5 to 200 nm. Therefore, stable and thin material membranes with pore diameters below 100 nm are desired for bioanalytical application on a single molecule level. The production of such membranes of macroscopic extensions is a technological challenge. Since the limit of conventional contact photolithograpy is around 8 00nm, other techniques are required for a high production rate of nanostructures in the future. In this study we have applied the hot embossing technique to produce 3D-nanostructures.

defects occur. This means that the fabrication procedure is suitable to generate pore arrays into a very thin membrane.

The fabrication process for «awo-pores is sketched in the insert of Fig. 2 including the following steps: 3.1 & 3.2 stamping, 3.3 dry etching, 3.4 resist stripping, 3.5 wet etching. The resist is very thin and impurities or in-homogenities in the material used have a big influence on the quality of the transfer process. As an example, the transfer of the 90 nm structures on PMMA can be incomplete as shown in Fig. 3.

Fig. 1: Nanochip with four nanopore membranes.

A picture of a nanochip ( lx l cm) is presented in Fig.l. The four membranes (white squares) on the chip can be seen by the naked eye. Although the membranes are only 300 nm thick, they are quite stable. In each of the four membranes arrays of pores were produced. We tried different arrays (2x2, 5x5) of various diameters (2 um, 1 um, 800 nm).

3.2

Fig. 3 : Nanopatterns produced by hot embossing in a PMMA resist (period 250 nm, pore diameter 90 nm).

When using an alternative resist, the surface of the resist becomes rough after stamping (Fig. 4). Here a pretreatment of the stamp surface and an improved stamping technique may be required.

8 a&sKhiji

Fig. 2: Membrane and the key processes for the fabrication of nanopores (insert)

In Fig. 2 a section of the membrane is shown with pores of 1 urn diameter, which are arranged in 5x5 arrays. These pores were produced by photolithographic techniques. The picture shows that the pores were very uniform and that no

Fig. 4 : Nanopatterns produced by hot embossing in an alternative resist (period 250 nm, pore diameter 90 nm).

These results demonstrate that hot embossing technique is suitable for nanochip production. However, many para­meters are more critical in nano-structuring processes and therefore require more time for optimization.

FUNDING: TopNAN021, PSI.

113

NANOPATTERNED MATERIALS FOR CELL ADHESION STUDIES

L. Heyderman, B. Ketterer, K. Vogelsang, L. Tiefenauer (PSI), M. Textor (ETH)

Cell adhesion on surfaces is dependent on the chemistry of the material as well as the topography. Molecules of interest bind selectively to titanium oxide. In order to investigate cell adhesion processes on a molecular level material-contrast features of nanometer dimensions will be generated using hot embossing techniques.

Little is known how cells react to adhesion contrasts in the nanometer range. In this project various features are generated aimed at directing or confining cells to predefined places. It is expected that the alignment of intracellular cytoskeleton is different, whether cells are cultured for instance on unconnected or connected nano-lines of metal oxide, respectively (see Fig. 1). The resulting cytoskeleton structure will determine directly many cell functions.

Adaptation of the cytoskeleton to the nanostructures

Fig. 1: Expected influence of nano-structures on cell adhesion. Black structures promote adhesion.

In a molecular view cell membrane proteins are responsible for adhesion processes and a clustering process is induced through cell-adhesive areas on the surface. Clustered proteins on the cell membrane are recognized as so-called focal adhesion points. Thus, the focal points on cells will directly be related to surfaces structures. Different patterns as sketched in Fig. 2 are generated on chips to be used for cell cultures and allow us to assess the impact of different nanostructures on cell functions.

— Nanolines 200 nm wide

- Micropads for ceils, 20 urn

I unconnected, | I anisotropic

Topography

Nanovalley

connected, isotropic Nanohill

The production of a sufficient amount of chips, which each has some hundreds of micro- and nano-structured features, is a technological challenge. The landing pads for cells will be 20 um, whereas the adjacent lines will only be 200 nm wide. The features will either be 20 nm above (hill) or below (valley) the mean surface level (see Fig. 2). Although many micro- and nano-structuring techniques are routine, their combination is difficult. A precise alignment of nano- to micro-patterns and the stability of the structured resist during the fabrication processes are major problems when different structuring techniques are combined.

As an alternative the transfer of the entire structure in one step will be developed in this project. First the micro- and the nanostructures are defined by e-beam and a stamp is produced allowing us to structure the thin resist on a whole wafer using hot embossing technique. Inhomogenities in the 300 nm thin resist have to be prevented on the whole area. First results are encouraging that well defined nanopatterns on large areas can be generated (Fig. 3). After etching nanovalleys and nanohills of metal oxides will be present on the surfaces, to which cell adhesion molecules bind selectively.

Fig. 3 : The embossed nano-lines structures in the resist are visible in the center.

This technological oriented fundamental project is an essential part in a framework. The modification and characterization of the surfaces are carried out by the group of M. Textor and cell adhesion studies are performed in the laboratory of J. Hubbell at the ETH. A close collaboration between the involved groups is required in order to realize such interdisciplinary experiments.

Fig. 2: Various design of micro- and nanopatterns for cell culture studies.

FUNDING: TopNAN021, PSI.

114

CHARGE TRANSPORT EFFECTS IN ELECTRODE COATINGS OF STREPTAVIDIN-FERROCENE CONJUGATES

B. Steiger, A. Grubelnik, C. Padeste, L. Tiefenauer (PSI)

The charge transport through electrode coatings of streptavidin-ferrocene conjugates was examined by cyclic voltammetry. The coatings exhibited fast charge transport. The rate of charge transport was compared to the rate of the electrocatalytic reduction ofH202 by microperoxidase-11 bound at the coating-solution interface.

Defined layers of streptavidin-ferrocene conjugates (Fc1 6-SAv) have been immobilized on electrodes in an effort to develop biosensors utilizing electrocatalysis as detection principle. In order to obtain optimal catalytic efficiencies that will give the optimum sensor performance, it is essen­tial to identify current-limiting processes. A key factor is the current density, iE, that measures the rate of electro­chemical charge transport (CT) through the coating. Cyclic voltammetry (CV) was used to study CT processes and to determine /E.

Fig. 1 shows CVs of a coating of 4 layers of Fc 1 6SAv at different scan rates (v). The anodic and cathodic current peaks (/p) are symmetrically shaped over the range of v = 0.025 - 1 V s 1 (A). A plot of ip vs. scan rate, v, is linear (B), and the charge under the peaks is independent of v. This is the expected behavior for fast CT through the coating where the total population of electroactive sites remains at or near thermodynamic equiUbrium at each applied potential.

P o t e n t i a l , m V v s . A g / A g C I S c a n R a t e , V s" 1

Fig. 1: (A) CV of an electrode coating containing 1.6 x 10"'°mol cm"2 of Fc sites (4 layers of Fc l 6SAv). (B) / in (A) vs. v.

Significant alterations in the shape of the CV („tailing") are observed at higher scan rates as shown for v = 8 - 51 V s"' (Fig. 2A). A plot of / vs. square root V is now linear (Fig. 2B). This means that the rate of CT is slower than the experimental time scale.

The slope of the plot in Fig. 2B was used to calculate iE. Analogous CV measurements with 1, 2, and 3 layers of Fc 1 6SAv resulted iE values for thinner coatings (Fig. 3). It can be seen that the theoretically generated iB-N dependence (dashed Une) is in good agreement with the observed values.

1 0 0 0 . ,

£ 8 0 0 . \

9" 6 0 0 - \

1 4 0 0 - V N & I 2 0 0 - - - - -

" o - L ^ — . — . — . — 1 2 3 4 5

N u m b e r of P r o t e i n L a y e r s , N

Fig. 3 : Current density (/E) that measures the rate of CT vs. number (TV) of layers of Fc l 6SAv.

Microperoxidase-11 (MP-11) is often employed for the preparation of bioelectrodes for the detection of H 2 0 2 . The performance of the electrocatalytic reduction of H 2 0 , by a monolayer of MP-11 immobilized on an electrode is known. The catalytic activity of MP-11 was used to probe /E as rate-controlling factor. MP-11 can be bound on top of the Fc 1 6SAv multilayers via biotin binding. Fig. 4 represents the limitation of the electrocatalytic activity by different values of iE. It can be seen that, up to ca. 10 mM of H 2 0 2 , the catalytic activity of MP-11 is not significantly limited by iE. The fast charge transport behavior of Fc 1 6SAv layers makes this component attractive to build up electrocatalytic systems on electrodes.

0 . 0 1 0 .1 1

[ H 2 0 2 ] , M

Fig. 4 : /E-modified catalytic activity of 5 x 10 1 2 mol cm"2

MP-11 immobilized on (Fc 1 6SAv)N vs. [H 2 0 2 ] .

Fig. 2: (A) Repeat of CV's of Fig. 2 at v = of 8, 10, 20, 34 ,41, and 51 V s"1. (B) / in (A) vs. vm.

115

MOLECULAR ARCHITECTURES FOR ENZYME SENSORS

C. Padeste, A. Grubelnik, B. Steiger, J. J. Hefii, L. Tiefenauer (PSI)

Molecular assemblies of ferrocene-labeled avidin (Fc-Av) with biotin-labeled redox enzymes offer a versatile route for the production of electrochemical biosensors. As a demonstrator system, Fc-Av in combination with biotinylated glucose oxidase (Bio-GOD) has been tested as a sensors for the detection of glucose.

The avidin-biotin system is widely used in biosenensorics to combine individual building blocks to functional assemblies. The high specificity and the very high binding constant of biotin to avidin allows a quick and stable functionalisation of avidin-coated surfaces with biotinyla­ted molecules such as enzymes or antibodies. For electrochemical sensors, however, the application of this versatile anchoring system is limited, due to the electrical insulation of the protein avidin.

Glucose Gluconolactone

Biotinylated Enzyme

Avidin-Ferrocene 1 i

Thin film gold electrode

2e"

Fig. 1: Scheme of the molecular assembly of Fc-Av/Bio-GOD sensors and reaction mechanism of ferrocene mediated glucose detection.

Binding of redox-mediators via flexible chains is a common route to enable the charge transfer through layers of proteins. In this work, ferrocene has been chemically bound to avidin and the resulting conjugates were immobilised on gold electrodes. To this first layer glucose oxidase was bound via biotin (Fig. 1). The response of this arrangement to glucose was tested in electrochemical experiments.

Cyclic voltammetry of the produced multilayes in phos­phate buffer revealed the oxidation and reduction of the bound ferrocene at about 250 mV (vs. Ag/AgCl). In glucose solutions additional electrochemical currents were measured in the potential range above 250 mV, which are attributed to the electrocatalytic oxidation of the glucose.

Electrodes with Fc-Av/Bio-GOD-assemblies were placed in an electrochemical flow cell. Into a constant flow of phosphate buffer 25ul volumes of glucose solutions were injected at a constant electrode potential (Fig 3).

3 Ü

Time

Fig. 3 : Response of Fc-Av/Bio-GOD assemblies to glucose in increasing concentrations (20-100mM). The molar ratio of Bio-GOD to Fc-Av: 0% for curve a, 15% (b) and 25% (c).

0 100 200 300 400 600 Potential (mV vs. Ag/AgCl)

Fig. 2: Cyclic voltammetry of a ferrocene-avidin/biotin-glucose oxidase Assembly on a gold electrode in a 10 mM glucose solution (dashed Une: in phosphate buffer).

The electrochemical response was found to increase with increasing enzyme content of the layers (curves a-c), and with increasing glucose concentration. In the low concentration range (0-10 mM) the signals increased almost linear while at higher concentrations (20-100 mM) the enzyme turnover limited the currents, resulting in a deviations from the linearity. No response of the system was found when avidin without coupled ferrocene was used to build the layers. The ferrocene is the key component needed to establish the electron transfer path from the enzyme to the electrode.

In summary, the results prove the activity of the molecular assemblies as enzymatic glucose sensors. By exchange of the redox enzyme it should be possible to adapt the specificity of the sensor to other analytes of interest.

116

A MODEL SYSTEM FOR THE TRIBOLOGY AND CORROSION OF S i 0 2

NANOTOWERS

B. Baumeister, T. Jung (PSI), E. Meyer (Univ. Basel)

Using SiO, nanotowers on Si as produced by interference lithography, key processes in fracture and wear have been studied. In addition to the quantification of perpendicular and lateral (frictional) forces, the influence of polar and corrosive liquids is detected. First applications are identified.

In fracture and wear, macroscopic behaviour is crucially determined by materials properties on the atomic scale. Here, fracture mechanics experiments are performed with microfabricated silicon-dioxide nanotowers on a Si-sub­strate using a scanning force microscope tip as a tool. Com­bined lateral force and topography investigations provide information about the Si/Si02-interface in fracture mecha­nisms and about the tip.

convolution of chemical and physical mechanisms in mechanical behaviour. This is relevant to composite materials ranging from composites on the macrometer scale like concrete down to nano-composites and brings our results to the core of tribological methods, i.e. to the context of corrosion, lubrication and wear. This analytical approach goes beyond our earlier research, which used this system for nanopatterning [1] and for wear studies [2].

14-1-

12-10 :

8 :

6 4

0+-0.0 0.5 1.0 1.5

Distance (um) 1 2 3 4

2.0

0.0 0.2 0.4 0.6 0.8 1.0 1.2 Distance (um)

Fig.l: A) Lateral forces measured on three nanotowers. B) Lateral force distribution and topography C) Assumed deflections (1-4) of a scanning tip at nanotowers.

25'

20

ß •a > I

10 20 30 40 50 60 70 Force (nN)

L i q u i d Th resho ld F r a c t u r e

Force (nN)

Coef f ic ient o f F r i c t i o n

Water 13 0.22

Hexyl alcohol 25 0.15

Silicone oil > 7 0 0.14

Fig.2: A) Threshold fracture forces in different solvents B) Experimentally determined force fractions in liquids of different polarity.

The mechanical strength of the studied material interface is relevant to "Silicon-on-Insulator" (SOI) device technology. The knowledge of mechanical properties of such interfaces in micro- and nanostructures can be relevant for future microelectromechanical systems (MEMS).

FUNDING: SNF, PSI, UNI BS.

The lubricative and corrosive influence of liquids with different chemical and physical properties is compared in abrasion and wear experiments. Both, the lubricative properties of the liquid and the ionic strength of solutions show characteristic influence on the threshold fracture forces. Using this new methodology the mechanical properties of interfaces on the nanometer scale will be related to chemical processes acting at the interface. Thus, these nanotowers serve as a model system, which shows the

REFERENCES

[1] B. Baumeister, T. Jung, E. Meyer Nanoscale fracture studies using the scanning force microscope. Appl. Phys. Lett. 78, 2485 (2001).

[2] B. Baumeister, T. Jung, E. Meyer Tribological studies on fracture and erosion of nanostructures. Tribol. Lett. 11,107 (2001).

117

MOLECULAR SOLID-GAS EQUILIBRIUM IN TWO DIMENSIONS

T. A. Jung, L. Patthey, R. Schelldorf er {PSI), S. Berner, M. de Wild, L. Ramoino, S. Schintke, A. Heuri, H.-J. Güntherodl(Univ. Basel), Ph. Aebi (Univ. Fribourg)

The adsorption of sub-phthalocyanine molecules on Ag(lll) has been studied by means of scanning tunneling micrsocopy (STM). The molecules are observed in different two-dimensional phases of adsorption which coexist in thermodynamic equilibrium.

Sub-monolayer coverages of chloro [sub-phthalocyaninato] boron(III) (SubPc) were deposited onto the A g ( l l l ) substrate by thermal sublimation. STM measurements at room temperature on samples with a coverage of 40% of a monolayer reveal 2D periodic islands [1]. In the STM-images individual SubPc molecules are resolved as triangular structures. The molecules self-organize in a 2D crystalline overlayer with a honeycomb pattern charac­terized by low packing density. In addition to the con­densed islands two more patterns can be distinguished (see Fig. 1).

time (comparable to the time required to scan over it), but tend to hop to nearby adsorption sites and form a 2D lattice gas. From time lapse imaging it could be shown that this lattice gas is in thermodynamic equilibrium with the con­densed phase.

a

t a ^ ^ ^ S M

I

b

UÀJoa s s g c g s

Fig. 1: (a) STM image showing the coexistence of different patterns of SubPc adsorbed on A g ( l l l ) (scan range 54x44nm, I=12pA, U=0.85V). The different patterns are as follows: (c) condensed island with honeycomb pattern; (g) noisy streak pattern; (s) SubPc stable adsorbed on substrate step edges. The dashed white line represents the location of the schematic cross-section, as shown in (b).

The noisy pattern next to the condensed islands are molecules on the same terrace, which exhibit mobility on the time scale of one scan line. In the line scan of Fig. 2 single molecules are clearly identified also in the noisy pattern. Therese molecules are stable adsorbed for a certain

0.6-f condensed phase noisy pattern

Fig.

15 20 x [nm]

2: (a) Image section taken from Fig 1 (range 38xl9nm). The white line shows the location of the cross section shown in (b).

The two distinctly different states of molecular adsorption of subPc on Ag as they have been identified here give rise to the question whether the actual bonding is different for 2D condensed or lattice gas states. In collaboration of Univ. Fribourg, and PSI synchrotron based X-ray photoelectron spectroscopy and X-ray photoelectron diffraction shall be used to further understand this issue. The understanding of conformational flexure [2] and molecular bi-stability at contacting interfaces is of key importance for tech­nologically functional devices like todays Organic Light Emitting Diodes (OLED) and future nanoscale molecular devices.

FUNDING: TOP NAN021, PSI.

R E F E R E N C E

[1] S. Berner et al., Chem. Phys. Lett. 348,175 (2001).

[2] T. Jung et. al., Nature 386,696 (1997).

118

ATOMIC FORCE MICROSCOPY CHARACTERIZATION OF SURFACES AND INTERFACES USED IN CATALYSIS, Si-Ge NANOSTRUCTURES, NEUTRON

MIRRORS AND X-RAY DIFFRACTION GRATINGS

R. Schelldorfer, O. Kirf el, U. Flechsig, F. Raimondi, A. Wokaun, R. Henneck, L. Heyderman, T. Jung (PSI), A. Serebrov (PNPI, Gatchina)

Atomic Force Microscopy (AFM) imaging provides a conclusive tool, which assists scientists to characterize processes and mechanisms, which occur at surfaces and interfaces. Two 'state of the art' instruments with different characteristics have been acquired atLMNfor 'baselab'support of internal projects, as shown below.

Scanning Probe Microscopy provides an excellent tool for the characterization of surfaces and interfaces. Beyond topographic imaging, also numerous electronic and chemical surface qualities can be imaged [1]. For the characterization of large patterned surface, as they are needed as for X-ray diffraction gratings for the SLS and for the characterization of intermediate steps of micro- or nanostructuring on whole semiconductor wafers, large sample imaging is crucial. First experiments reveal the manufacturing quality of Zeiss X-ray gratings and of Ge dots on Si.

The second atomic resolution instrument is dedicated to experiments on smaller samples and can provide information on several materials like mechanical surface elasticity, electric and magnetic surface fields as well as deformations and frictional forces down to the atomic scale.

In a detailed study, ex-situ AFM revealed characteristic differences in the surface morphology of a Cu-/ZnO/Si model catalyst before and after vacuum annealing and the Cu-free ZnO/Si substrate. The surface of the cleaned substrate presents a low roughness with grains having a diameter of 60-80 nm. Deposition of Cu leads to an increase in roughness while the lateral dimension of the grains remains unchanged. After annealing at 670 K the lateral dimension of the grains is increased to 150 nm, while a further increase of roughness takes place. In continuation of this study, the catalytic activity of these surfaces will be related to the preparation parameters to further optimize these surface properties.

Ultracold neutron (UCN) mirrors: for the PSI high-intensity UCN source we will use a large (2 m3) intermediate storage vessel coated with Be. In order to study the UCN reflectivity and potential loss mechanisms, it is necessary to analyze the surface on a sub-micron level as the coherence length for reflection corresponds to the neutron wavelength of about 50 to 100 nm. Fig. 1 shows the example of a stainless steel sheet (mechanically and electro-polished), coated with a 300 nm thick layer of Be deposited by magnetron sputtering. It can be seen from the profile that the local gradients are at most - 5° and thus introduce only a negligible contribution (for a storage vessel) due to non-specular, diffuse reflection.

? 0 0.25 0.50 0.75

Fig. 1: Surface roughness of neutron mirrors.

These projects demonstrate the qualities of atomic force microscopy in 3D mapping of surface topography and properties. Scanning probe microscopy often gives conclusive experimental access to quantitative 2D information, which cannot be gained from either optical or electron microcopy. Further initiatives for collabortions using this nanotool are welcome.

REFERENCE

[1] T. Jung, F. Himpsel, et. al. Chemical Information from Scanning Probe Microscopy and Spectroscopy. In 'Scanning Probe Microscopy, Analytical Methods, ed. R. Wiesendanger, Springer Berlin, 11 (1998).

119

L a b o r a t o r y f o r R a d i o - a n d

E n v i r o n m e n t a l C h e m i s t r y Foreword

Heavy Elements

Surface Chemistry

Analytical Chemistry

Cement Chemistry

Project Radwaste

120

LABORATORY FOR RADIO- AND ENVIRONMENTAL CHEMISTRY

H.W. Gäggeler (Univ. Bern & PSI)

Already for the third time we succeeded to perform a first chemical investigation of a member of the periodic table, the element with atomic number 108, named hassium (Hs), the latin expression for Hessen in Germany. On the basis of only 7 detected atoms of hassium it was possible to prove its similarity to osmium, a member of group 8, based on the formation of a very volatile tetroxide molecule. This achievement was possible thanks to a technological boost in form of a novel cryo-thermochromatography detector, jointly built with the Lawrence Berkeley National Laboratory and the Laboratory of Micro- and Nanotechnology - a real textbook example of a fruitful collaborative effort by different research units at PSI.

Highest public attention, however, received another activity, the successful deep Ice core-drilling at a glacier-site between the two Belukha summits in Siberia at an altitude of about 4100 m asi. As a result of the data gained from a shallow firn core drilled in summer 2000 we decided to go one step further and try "the impossible". The reason for the high risk of such a campaign comes from the generally poor weather conditions in the Altai mountains.

Thanks to the perfect organization by Margit Schwikowski together with the help of a group of friends from the Siberian branch of the Academy of Science of Russia in Barnaul, led by Tatjana Papina, as well as excellent helicopter pilots, the entire adventure ended in a full success. Generations of Ph.D. students and post-docs will now have the unique opportunity to analyse ice cores from an unexplored area of the world, notably the most continental mountain area worldwide.

Also the third PSI group engaged in basic research made considerable progress in surface chemistry. The new chemical ionization mass spectrometer became operational. This device uses the properties of ion-molecule interactions to measure species of interest at the ppb level. This ultra­sensitive spectrometer complements the radiochemical tracer technique. In addition, on November 29, for the first time the new PROTRAC transport Une delivered [ 1 3N]NO to the chemistry laboratory at a level of some 3x l0 7 radio-labelled molecules per second. Also the SINQ gas-jet device proved again to be a versatile tool for studies with 8 4Br-labelled species, e.g. on surfaces of deliquescent NaBr particles.

On the other hand, the neutron activation analysis device at SINQ fails to be competitive to other similar devices worldwide. The rather low thermal neutron flux and a high intensity of high-energy neutrons clearly restrict its field of application. In some special cases, however, the high-energy neutrons may serve for production of neutron-poor isotopes: in an ongoing project Pb targets were irradiated at the NAA-SINQ device, in order to form in (n; Dxn) reactions short-lived Hg tracer isotopes.

Accessibility to irradiated targets of PSI-West was the basis of a joint project of our applied radiochemistry group RadWaste with ISOLDE at CERN. An irradiated graphite target was prepared as ion source and proved to deliver as much as 300 nA peak current of 7 Be at CERN, to our knowledge a world record!

121

DECAY PROPERTIES OF 2 6 9 H s AND EVIDENCE FOR THE NEW NUCLIDE 2 7 0 H s

A. Türler, Ch.E. Düllmann, H.W. Gäggeler, S. Soverna (Univ. Bern & PSI), R. Dressler, B. Eichler, F. Glaus, D.T. Jost, D. Piguet (PSI), D.M. Lee, T.N. Ginter, K.E. Gregorich, U. Kirbach, R. Sudowe, (LBNL), D.C. Hoffman,

H. Nitsche, J.B. Patin, P. Zielinski (UC Berkeley & LBNL), W. Brüchle, R. Eichler, E. Jäger, V. Pershina, M. Schädel, B. Schausten, E. Schimpf, H.-J. Schott, G. Wirth (GSI), A.B. Yakushev, S.N. Timokhin (FLNR), K. Eberhardt, P. Thörle, N. Trautmann (Univ. Mainz), Qin Zhi (IMP Lanzhou), A. Vahle (FZRossendorf)

In bombardments of Cm with 145-MeV Mg ions, '°yHs and "uHs were produced with cross sections of =6 pb and =4 pb, respectively. After chemical isolation, Hs atoms were identified by observing genetically linked nuclear decay chains. Three chains originating from 269Hs confirmed the decay properties observed previously in the decay of •yyy 07f) ")7f\

112. Two chains exhibited the characteristics expected for the new nuclide Hs. The nuclide Hs was predicted to be the next heavier "doubly-magic" nucleus after mPb. From the measured E¿=9.16±u.03 MeV an a-decay half-life of 2-7 s was estimated.

Three decays of the nuclide Hs were observed by Hofmann et al. [1,2] as grand daughter of 2 7 7 112 . The deduced relatively long half-life of about 10 s make 2 6 9 Hs an ideal candidate for first chemical experiments with hassium (element 108). 2 6 9 Hs can be produced directly in the reaction 2 4 8 Cm( 2 6 Mg, 5n). In the 4n de-excitation channel, the new nuclide 2 7 0 Hs is produced, which was predicted to be the next heavier "doubly-magic" nucleus after 2 0 8 Pb [3]. Its decay properties are of great interest to nuclear physics.

2 6 9Hs 2 6 9Hs ^'Hs O l . O l .

2 e eSg 1» 9.18 MeV (3B)

2 6 5Sg f 8.88 MeV(3T)

2 e eSg C(2 . C(2 .

'9.10 MeV (3B)

8.69 MeV (3T) 4.4 s

8.90 MeV (3B) 17.1 s

'8.50 MeV (ST) 2.4 s

'8.50 MeV (3B) 0.846 s

'8.68 MeV (3B) 9.3 s

3Fm

8.21 MeV (3T) 55.6 s Dató: 13-May-2001

Time: 10:02:07

94MeV(3T) 85MeV(3B) 7.9 s

Dató: 12-May-2001 Time: 22:00:28

Date: 12-May-2001 Time: 09:55:03

27°Hs 27°Hs <«1 .

f9.16MeV(2T) 2 6 6Sg 2 6 6Sg

C(2 .

8.97 MeV (4B)

'8.66 MeV (2T) 25.7 s

'8.64 MeV (4B) 11.9 s

94 MeV (2T) 93 MeV (2B) 94 MeV (4T) 92 MeV (4B) 0.199s 1.2 s

In order to investigate the chemical properties of Hs, the gas chromatographic separation system IVO (In situ Volatilization and On-line detection) [4] and the cryo on­line detector (COLD) [5] were set up at the rotating target-and window irradiation facility of the UNILAC at GSI Darmstadt. Hs is expected to belong to group 8 of the periodic table of the elements and should thus form very volatile H s 0 4 molecules. Test experiments with short-lived Os isotopes, the lighter homologue element of Hs, showed that O s 0 4 molecules were formed when the recoiling Os nuclei were stopped in a mixture of He and 0 2 .

In the course of the experiment, data was collected during 64.2 h and a beam integral of l.OxlO 1 8 2 6 Mg ions was accumulated. The count rate in all detectors was very low. Only the nuclides 2 1 9 Rn, 2 2 0 Rn, 2 1 'At and their decay Fig. 1: Decay chains attributed to the decay of Hs-nuchdes. products were identified after chemical separation. While

1 1 At (and its decay product 2 1 'Po) was deposited mainly in 219 220

the first two detectors, Rn and Rn and their decay products accumulated in the last three detectors, where the temperature was low enough to condense Rn. Due to a defect, one side of detector sandwich 1 was not operating and was therefore excluded from the data analysis. The average count rate per detector pair was 0.6 h"1 in the relevant a-decay energy window E a=8.0-9.5 MeV in detectors 2 through 9.

Dale: 12-May-2001 Time: 02:33:08

Dale: 12-May-2001 Time: 17:09:09

The data analysis revealed one four-member- and 4 three-member decay chains (Fig. 1) which all occurred within a time period of less than 70 s and which all have random probabilities of less than 7xl0~ 5. The 4-member and the 3-member a-decay chains were attributed to the decay of the nuclide 2 6 9 Hs, since these almost perfectly match the decay properties observed previously by Hoffman et al. [1] (except for the low a-decay energy of 2 6 9 Hs in the three member decay chain). Three decay chains were terminated by spontaneous fission. From the previously known decay

data such a signature would be expected only for the decay of the new nuclide 2 7 0 Hs. But, one of the terminating S F events had a rather long life-time of 7.9 s, which is not very likely for 2 6 2 Rf with a half-life of 2.1 s. A similar decay sequence has also been observed in one of the decay chains assigned to 2 7 7 112 [2]. Therefore, this chain was attributed to 2 6 9 Hs. Noteworthy are the very unusual decay properties of 2 6 1 Rf [6]. We tentatively assigned the remaining two decay chains to the new nuclide 2 7 0 Hs. From the measured E a=9.16±0.03 MeV an a-decay half-life of 2-7 s was estimated.

REFERENCES

[1] S. Hofmann, et al., Z. Phys. A 354, 229 (1996). [2] S. Hofmann, et al., Rev. Mod. Phys. 72,733 (2000). [3] Z. Patyk et al., Nucl. Phys. A 533,132 (1991). [4] Ch.E. Düllmann et al., NIM A (in press). [5] Ch.E. Düllmann et al., this Annual Report. [6] R. Dressier et al., this Annual Report.

122

EVIDENCE FOR ISOMERIC STATES IN 2 6 1 R f

R. Dressier (PSI), A. Türler (Univ. Bern & PSI)

•yir j 977 9/iQ

Evidence for a new isomeric state Rfwas extracted from experimental data of 112 and Hs decay. The a-decay energy of 8.5 MeV and half-live of 4.1 s fits well with decay-energy half-live systematic and suggest that this new state is actually the ground state. A spontaneous fission branch of 40 % can be extracted. Implications for the decay

c266 properties of Sg are discussed.

The element 112 was discovered by the SHIP group at GSI in 1996 [1]. Up to now three decay chains of the isotope 277112 were observed [2]. At least two of them exhibit very uncommon decay properties of 2 6 1 Rf as a member of the decay chains. In Tab. 1 the decay properties of these chains starting with z o y Hs down to Z 0 1 Rf are given.

During the first ever chemical investigation of the element Hs [3] three decay chains of 2 6 9 Hs were observed. This isotope is like 2 6 1 Rf a member of the 2 7 7 112 decay chain. All of the Hs events show similar surprising decay properties for 2 6 1 Rf as observed in the 112 experiments (see Tab. 1).

Table 1: Partial decay chains of 2 7 7 112 and 2 6 9 Hs taken from [1-3] (esc denotes escape-events).

[1] [2] [3] [3] [3] 2 6 9 Hs E [MeV]

t [ s ] 9.23 19.7

9.18 22.0

9.18 8.88 9.10

2 6 5 S g E [MeV] t [ s ]

esc 7.4

esc 18.8

8.69 4.42

8.90 17.1

8.68 9.32

2 6 1 Rf E [MeV] t [ s ]

8.52 4.7

SF 14.5

8.50 2.36

8.50 0.84

SF 7.92

Therefore, both experiments are in contradiction to the up to now known decay properties of 2 6 1Rf. B. Kadkhodayan [4] determined its half-live to be 7 8 + 1 1 . 6 s and established an upper limit for the spontaneous fission (SF)-branch of 11%, whereas Yu.A. Lazarev [5] showed that 2 6 1 Rf decays by emission of a-particles with energy of 8.28±0.03 MeV with more than 98 %. In all of these investigations 2 6 1 Rf was produced directly using heavy ion induced fusion reactions.

S. Cwiok and collaborators calculated single-particle Nilsson levels using the Hartree-Fock-Bogoliubov method with a Skyrme force and a pairing interaction proposed by Lipkin and Nogami [6]. In Tab. 2 the results for the ground state and some of the first excited levels of 2 6 9 Hs, 2 6 5 Sg , 2 6 1Rf, and 2 5 7 N o are given [7].

Table 2: Single-particle Nilsson levels taken from [7] (g.s. ground-state).

Nilsson level

Excitation energy [MeV] Nilsson level 2 6 9 Hs 2 6 5 s g

2 6 1 R f 2 5 7 N o

11/2" [725] g.s. g.s. 0.3234 0.6985

9/2 + [615] 0.0945 0.0714 0.4266 0.8709

7/2 + [615] 0.4339 0.0156 g.s. 0.1253

3/2 + [622] 0.7219 0.4337 0.2422 g.s.

Due to the parity and spin conservation during the a-decay, the most probable transition connects states with the same

quantum numbers. Two different decay paths of 2 6 9 Hs can be distinguished, which differ in the opposite parity of the involved states. These paths are given in Fig. 1 in a sche­matic way.

2 6 9 H s

9/2+. • 9 / 2 +

1 1 / 2 -

Fig. 1: Schematic view of the decay paths of 2 6 9 Hs

states of Rf and No are 2 6 1Rf, for the 7/2 +

If the transition between the 11/2 assigned to the known decay properties of ground state decay an a-energy of 8.53 MeV can be ex­tracted, which is close to the observed value. A half-live of 4 . 2 + 4 1 _ u s (68 % confidence) results from all events, whereas the a-branching is only 60 %.

These decay properties fit well with the half-life predictions by B. Buck [8], which takes into account the spin states. For the ground state transition with 8.52 MeV a half-life of 7.32 s and for the isomeric state with 8.28 MeV a half-live of 74.9 s was calculated. Both predictions are in good agreement with the experimental data and, therefore, support the assignment to different isomeric states.

These decay properties of 2 6 1 Rf alter the view of some older experimental results. In [9] all known decay chains of 2 6 6 Sg were used to determine the a-decay properties of this iso­tope. A probability analysis leads to two roughly equal strong a-lines at 8.59 MeV and 8.72 MeV, which is a sur­prising result for an even-even nucleus. However, the as­signment to the decay of 2 6 6 S g based only on the assumed decay pattern of a high energetic a-particle shortly fol­lowed by a SF-event. From the discussion above follows, that the decay of 2 6 5 S g can exhibit such a pattern if the decay starts from an even parity state in 2 6 5 Sg. So, it is highly possible that in this case the high energetic a-line originate from 2 6 5 Sg .

REFERENCES [1] S. Hofmann et al., Z. Phys. A 354, 229 (1996). [2] S. Hofmann et al., Rev. Mod. Phys. 72,733 (2000). [3] Ch. Düllmann et al., this Annual Report. [4] B. Kadkhodayan et al., Radichim. Acta 72, 169 (1996). [5] Yu.A. Lazarev et al., Phys. Ref. C 62, 064307 (2000). [6] S. Cwiok et al., Phys. Rev. Lett. 83, 1108 (1999). [7] W. Nazarewicz, private communication 2001. [8] B. Buck et al., J. Phys. G 18, 143 (1992). [9] R. Dressler et al.,

Ann. Rep. Univ. Bern & PSI 1999, p. 6.

123

CHEMICAL INVESTIGATION OF HASSIUM (Hs, Z=108)

Ch.E. Diillmann for a Univ. Bern - PSI - GSI - JINR - LBNL - Univ. Mainz - FZR - IMP - collaboration

2Ó9 2 TO For the first time, a Hs containing compound has been investigated chemically. The isotopes Hs and Hs were produced in the reaction Cm( Mg;5,4n) ' Hs at the UNILAC at GSI in Darmstadt. They were in-situ con­verted to highly volatile HsÖ4 which was transported in the gas phase to the detection apparatus COLD where the nuclear decay of the Hs isotopes and their daughter products was registered. HSO4 was deposited at a temperature of (-44±5) °C while OSO4 was deposited at (-82±5) °C under the same experimental conditions. From these values, AHads(Hs04)=(-46±3) kJ mol1 (95 % ci.) and AHads(OsO4)=(-39.5±1.0) kJ mol1 were deduced. With the formation of a very volatile tetroxide, Hs behaves as expected and is a typical member of group 8 of the periodic table.

1 INTRODUCTION

The heaviest element, whose chemical behavior has been studied so far is bohrium (Bh) with Z=107 [1] behaving like a typical member of group 7 of the periodic table. The longest-living a-decaying isotope of the next heavier element hassium (Hs, Z=108) is 2 6 9 Hs (T. /2=11.3 s) which has been identified in the decay chain of 2 7 7 112 [2, 3]. Hs is supposed to be a member of group 8 of the periodic table of the elements and should thus form a very volatile tetroxide. Relativistic density functional calculations predicted the electronic structure of H s 0 4 to be similar to the one of O s 0 4 [4]. Application of different semiempirical models of the interaction of a M e 0 4 molecule with quartz surface predicted the adsorption behavior of O s 0 4 and H s 0 4 to be very similar [4]. Extrapolations of trends within group 8 of the periodic table also predicted H s 0 4 and O s 0 4 to behave similar in a gas adsorption chromatography experiment [5]. Hs isotopes were produced directly in the reaction 2 4 8 Cm( 2 6 Mg;5,4n) 2 6 9 ' 2 7 0 Hs with cross-sections of 6 pb and 4 pb (within a factor of 3), respectively [6].

2 EXPERIMENTAL

A detailed description of the experimental techniques used for the production and detection of Hs isotopes is given in another contribution to this annual report [6].

3 RESULTS

Seven decay chains were detected in the course of the experiment which were attributed to 2 6 9 Hs or the so far unknown isotope 2 7 0 Hs [6]. Using the newly built Cryo On-Line Detector COLD (an improved version of the Cryo-Thermochromatography Separator CTS developed at Berkeley [7]) the deposition temperature of the Hs containing molecules was determined to (-44±5) °C giving strong evidence of the formation of Hs0 4 . In an irradiation of a 1 5 2 Gd target, 1 7 2 0 s (T./2=19.2 s) was produced in the reaction 1 5 2Gd( 2 6Mg;6n) and a deposition temperature of (-82±5) °C was measured for 1 7 2 0 s 0 4 . The deposition distribution in the COLD array along the detector pairs is shown in Fig. 1. The white area indicates decays originating from either 2 6 9 Hs or 2 7 0 Hs where a definite assignment to either isotope was not possible. From these temperatures the adsorption enthalpy was deduced by applying a Monte-Carlo simulation based on a microscopic description of the transport process in the chromatography column [8], i.e. in the COLD system.

1 2 3 4 5 6 7 8 9 10 11 12

Detector number

Fig. 1: Merged thermochromatograms of O s 0 4 and Hs0 4 . The solid Unes represent results of a Monte-Carlo Simulation with AH a d s values of -39.5 kJ-mol"1

(Os0 4 ) and -46 kJ-mol"1 (Hs0 4 ) , respectively. The dashed line indicates the temperature gradient.

Since the half-Ufe of the nucüde is a crucial parameter in this simulation and this value has not yet been measured for 2 7 0 Hs, only the three events assigned to 2 6 9 Hs were used for the simulation. AH a d s(Hs0 4)=(-46±3) kJmol"1 (95 % ci . ) was evaluated, compared to AH a d s(OsO 4)=(-39.5±1.0) kJ-moi"1. The latter value is in good agreement with AH a d s (Os0 4 )= (-38.0±1.5) kJmol"1 evaluated in earüer experiments.

4 DISCUSSION

Hs was shown to form a very volatile oxide, presumably Hs0 4 . Therefore it behaves like a typical member of group 8 of the periodic table.

REFERENCES

[1] R. Eichler et al., Nature 407, 63 (2000). [2] S. Hofmann et al., Z. Phys. A 354, 229 (1996). [3] S. Hofmann et al., Rev. Mod. Phys. 72, 733 (2000). [4] V. Pershina et al., J. Chem. Phys. 115, 792 (2001). [5] Ch.E. Diillmann et al., J. Phys. Chem. A (submitted). [6] A. Türler et al., this Annual Report. [7] U. Kirbach et al., Nucl. Instrum. Meth. A (in press). [8] I. Zvara, Radiochim. Acta 38, 95 (1985).

124

PHYSISORPTIVE INTERACTION OF M e 0 4 (Me=Os, Hs) WITH QUARTZ SURFACE

CLE. Düllmann, H.W. Gäggeler, A. Türler (Univ. Bern & PSI), B. Eichler (PSI), R. Eichler (GSI)

The behavior of Hs04 in a gas adsorption chromatography experiment was studied theoretically assuming that physisorptive forces will govern processes taking place in the chromatography column. By linking the interaction distance with the binding energy, the adsorption distance of Os04 was calculated and shown to be the same as the one of noble gases on metal surfaces within the margin of error. Using this distance and calculated molecular properties ofHs04, the interaction energy and hence the enthalpy of adsorption was calculated

1 INTRODUCTION

The interaction of symmetric molecules with a dielectric solid, as in case of the adsorption of M e 0 4 (Me=Os, Hs) on a quartz surface, involves mainly dispersion forces. Attraction due to physisorption forces is described in [1] and can be written in the form

E ( r ) = - C , / r 6 (1)

where E ( r ): interaction energy [eV]; Q : van der Waals constant between two systems ; r: interaction distance [cm].

The total interaction between a molecule and a slab of infinite extent and depth can be obtained by a summation over all moleule-molecule interactions if simple additivity of forces can be assumed [1]. The summation can be replaced by a triple integration. Eq (1) then has the form

E ( 0 = - (2)

where N: number of atoms per cm

Generally for two different types of interacting molecules (1) and (2), C, is [2]

C-1 * C C l * OC >y

2

JDT(1) 'DT(2)

^ D T ( l ) + E D T(2) (3)

where a: polarizabilities of the molecules (1) and (2) [cm 3]; E D T : average dipole transition energy of the molecules [eV].

The polarizability of quartz can be calculated from the well-known equation for solids [3] a 3 ( e - 1 )

2 4 - 7 t - N ' ( e + 2) where e: dielectric constant of the solid. Introducing (3) and (4) into (2) yields

(4)

E ( 0 = 3 a

16-r 3 (e + 2)"

J DT(2)

^ D T ( l ) + E DT(2) (5)

For the calculation of E D T , Pauling found empirically [4]

E O T = 1 . 5 7 - n > (6)

where IPi: first ionization potential [eV].

E ( r ) can directly be related to the enthalpy of adsorption (AH a d s) determined in gas adsorption chromatograhpy experiments. Taking into account the different number of degrees of freedom in the respective models [5], it follows

£(,) =-Äff ,* + 0.5-R-T (7)

Where AH a d s: enthalpy of adsorption, R: universal gas constant, T: temperature.

2 CALCULATIONS

Using the experimental value (-38.0±1.5) kJ-mol"1 [6], the interaction distance of O s 0 4 on quartz surface was determined to r(OsO4)=(0.260±0.003) nm. The VAN D E R W A A L S radius r V D w(Os0 4 ) can be calculated from critical data [7] to 0.1731 nm. Therefore, r(Os0 4) exeeds T V D W ( O S 0 4 ) by 0.0869 nm. From literature values [8, 9] for the adsorption enthalpies of 5 noble gases on 15 different metals, the respective interaction distances were calculated. The mean distance turned out to be independent of both the noble gas and the metal involved and was determined to (0.2468±0.021) nm [10], in agreement with the value for O s 0 4 within the margin of error. Recently, fully relativistic DFT calculations have been performed for molecular properties of H s 0 4 [3]. a(HsO 4)=8.46-10 _ 2 4 cm 3 and IPi(Hs0 4)=12.27 eV are reported [3]. Using these values and the universal interaction distance r=(0.2468±0.021) nm, AH a d s (Hs0 4 ) can be calculated applying eqs (5)-(7) to AH a d s (Hs0 4 )=(-47±ll) kJ-mol"1. Applying the same procedure, AH a d s (Os0 4 )=(-47±ll) kJ-mol"1 is calculated.

3 DISCUSSION

Both O s 0 4 and H s 0 4 are expected to behave similarly in a gas adsorption chromatography experiment. This behavior can be understood if it is assumed that the adsorption behavior of the tetroxides is mainly determined by the tetrahedral oxygen configuration and the only slightly increasing polarizability in the order Os0 4 <Hs0 4 . The influence of the variation of the metal on the polarizability and therefore on the adsorption behavior is then expected to be small.

REFERENCES

[1] A. Adamson, Physical Chemistry of Surfaces. 4 t h Ed., Wiley and Sons: New York, 1982; Chapter VI.

[2] D. R. Lide, Ed. CRC Handbook of Chemistry and Phy-sics. 82 t h Ed.; CRC Press: New York 2001; Chapter 10.

[3] V. Pershina et al., J. Chem. Phys. 115, 792 (2001). [4] L. Pauling et al., J. Chem. Phys. 20, 29 (1952). [5] Ch. E. Düllmann et al., J. Phys. Chem. A. (submitted). [6] Ch. E. Düllmann et al., Nucl. Instrum. Meth A (in

press). [7] K. Schwabe, Physikalische Chemie, Akademie-Verlag

GmbH: Berün, 1973; Band 1, Chapters 4, 5. [8] A. R. Miedema et al., Surface Sei 104, 491 (1981). [9] B. Eichler et al., Isotopenpraxis 21 ,180 (1985).

125

MODEL STUDIES WITH MERCURY FOR A FUTURE 112 EXPERIMENT

S. Soverna, Ch.E. Düllmann, H.W. Gäggeler, A. Türler (Univ. Bern & PSI), B. Eichler, D. Piguet, L. Tobler (PSI), Q. Zhi (IMP, Lanzhou, China)

Determination of the adsorption enthalpies of Hg on different noble metals were performed by thermo-chromatography with long-living Hg-isotopes that were produced in the Spallation Neutron Source SINQ at PSI

1 INTRODUCTION

After the discovery of long-living superheavy elements in Dubna, Russia, the investigation of their chemical properties becomes feasible. First chemical studies are concentrating on element 112. There are different predictions for the chemical and physical properties of element 112. Based on classical extrapolations element 112 behaves similar to Hg. However, there are predictions in the literature that element 112 could behave like a noble gas [1]. Consequently, a future 112-experiment has to embrace both predictions. In this contribution model studies are based on the assumed similarity to Hg and the best suitable surface to adsorb Hg was searched. Theoretically such a surface can be found based on the calculated adsorption enthalpies of Hg on different metals [2]. However, some other properties are of importance. To get a metal-metal-bond, metals are needed which do not oxidise, such as noble metals.

2 EXPERIMENTAL

The thermochromatographic experiments were carried out with long-living Hg-isotopes which were produced in the Spallation Neutron Source SINQ at PSI. Natural Pb was irradiated with spallation neutrons and the excited Pb-atoms evaporated surprisingly up to 12 neutrons so that the Pb-isotopes 192 and 193 were produced. These ß+-active Pb-isotopes decayed via Tl- into Hg-isotopes. These Hg-isotopes were evaporated from the irradiated Pb at 500°C and deposited on a Au-foil at RT (Fig. 1).

Pb with

Ar/H2

• a 50 ml/min

192, 193 Hg quarzwool

kujoil

^ 1 J / filter

|^ ffi ffi ffi

Hg-isotopes. In order to remove trace amounts of 0 2 and H 2 0 , the gas was passed through a gas drying unit, filled with molecular sieve, and through two Ta metal getter (at 1000°C), one was placed just before the thermo-chromatographic column and the other was placed directly into the column. After 1 h the deposition of the Hg-isotopes along the temperatur gradient was determined measuring their activity with a Geiger-Müller counter.

3 RESULTS

The Hg-isotopes were found on Pd at a deposition temperature of 270 + 20 °C, on Pt at a temperature of 216 + 25 °C and on Au at a temperature of 115 + 30 °C (Fig. 3).

10 20 30 40 50 60 Length of metal column [cm]

Fig. 3 : Thermochromatogram of Pt.

192, 193 Hg on Pd, Au and

Table 1: Deposition temperatures (T) and calculated adsorption enthalpies (AH a d s > c a. c.) together with the expected adsorption enthalpies (AH a d s > e x p t .) [1].

Fig. 1: Separation of Hg from the activated Pb-target.

Surface T [°C] Pd 270 + 20 -132kJ/mol -206 kJ/mol Pt 216 + 25 -117kJ/mol -167kJ/mol Au 115 + 30 - 92kJ/mol -114kJ/mol

This Au-foil was then placed at the start position of the thermochromatographic column (Fig. 2).

Au-foil Ta-getter

Ar/Hl^ \®®&»^\®&¡»®}(®®®® »

metal (Pt, Au, Pd)

.50 ml/min i®o®®i®i®®®®ir®®8o o o o ® \ water cooling cooling

Fig. 2: Thermochromatographic column which was lined with the metal-surface to be investigated.

Prior to the experiment, the metal-surfaces in the columns were reduced and cleaned in a separate oven at 900 °C in the same gas mixture of Ar/H2 (Vol%:97/3). The temperature gradient of the column ranged from 600 °C to -10 °C. The Au-source was heated to 900°C to release the

The adsorption enthalpies (AH a d s c a l c ) have been calculated from the measured deposition temperatures using the mobile adsorption model [3]. For Au and Pt these values agree reasonable well with the expected values (AH a d s e x p t ) . For Pd we observe a large difference between the expected and the calculated values. This difference could be due to the H2-co-adsorption on the Pd surface. Despite this fact, the sequence of the adsorption enthalpies is found as predicted: Pd > Pt > Au .

REFERENCES [1] K. S. Pitzer, J. Chem. Phys. 63, 1032 (1975). [2] Calc. analogous to H. Rossbach et al, ZfK-527 (1984). [3] B. Eichler, I. Zvara, Radiochimica Acta 30, 233 (1982).

126

THERMOCHROMATOGRAPHIC INVESTIGATION OF Rh AND 1 0 7 R h WITH DIFFERENT CARRIER GASES

F.L. Haenssler (Univ. Bern), Ch. E. Düllmann, H.W. Gäggeler (Univ. Bern &PSI), B. Eichler (PSI)

On the long way to identify Meitnerium chemically, first steps were made by studying the chemical and physical behaviour of its homologues Rhodium with thermochromatographic methods. It could be shown that the compound RhClj is volatile and that the measured enthalpies of sublimation are in accordance with literature values.

1 INTRODUCTION

Meitnerium (Mt) is one of the elements that has not been placed in the periodic system yet. Mt was first detected in 1982 by G. Miinzenberger produced in the reaction of 2 0 9 Bi with 5 8 Fe projectiles [1]. All isotopes of Meitnerium are very unstable (Ti /2 = 0.7 s). To position Mt in the periodic table and to make predictions about its behavior, Rhodium was studied using the gas thermochromatography technique. Thermochromatography is a well established method to separate small amounts of compounds with different volatilities [2] and to determine either the enthalpy of adsorption (AH a d s) for carrier-free radionuclides [3] or the enthalpy of sublimation (AH s u W) for macroscopic amounts [4].

2 EXPERIMENTAL

The aim of this study was to produce and sublimate the two substances R h 2 0 3 and RhCl3. Therefore, i)small amounts of Rhodium powder or ii)microscopic amounts of 1 0 7 Rh that were collected on a quarzfilter from the 2 5 2 Cf fission source "Miss Piggy" were placed in quartz columns. The columns were placed in an apparatus, which consisted of two ovens. In the first oven the powder reacted with the gases and sublimated. In the second thermochromatography oven the substance deposited at a given temperature. For the production of R h 2 0 3 a mixture of He and 0 2 and for RhCl3

either Nitrogen with SOCl 2 or a mixture of N 2 and 0 2 with SOCl 2 were used as carrier gases. Some of the parameters like the duration of the experiment, the flow rate of the gases, the composition of the gas or the temperatures of the ovens were varied. In the experiments with macroscopic amounts, rings of different colors were visible on the inside of the tubes. With the help of a model [4] the enthalpies of sublimation were calculated by evaluating the temperature of deposition of the rings. After the experiments with earner- free 1 0 7 Rh, the tube was scanned segment-wise for one minute per centimeter with a y-detector to obtain a chromatogram.

3 RESULTS AND DISCUSSION

The experiments showed that it was not possible to sublimate macro amounts of R h 2 0 3 or carrier- free 1 0 7 RhCl 3

up to a temperature of 1000°C. 1 0 7 Rh had to be transported with carbon aerosol particles out of the radionuclide source "Miss Piggy". The carbon reduced 1 0 7 Rh, therefore Rhodium did not react with the chlorinating gas. The experiments with inactive rhodium and with RhCl3 as carrier substance on the other hand showed two clear rings in the tubes.

40 50 60 70 Lenght [cm]

80 90

Fig. 1: A typical chromatogram for the sublimation of 1 0 7 RhCl 3 with carrier substance. The bars show the positions of the detected rings. The first set is probably pure Rhodium that comes from dissociated RhCl3. The second shows the position of theredRhCl 3.

Red rings were found in a temperature range between 780°C and 820°C. With the literature value of 250 ± 12 J/Kmol for AS s u W the values for AH s u b l were calculated as 331 ± 10 kJ/mol. Compared with the mean value of four literature values (356 ± 12 kJ/mol, 365 kJ/mol, 347 kJ/mol and 291 kJ/mol) of 340 ± 33 kJ/mol it is highly probable that the observed red rings are in fact RhCl3. Although it was possible to evaporate macro amounts of RhCl3 this system can not be used for future experiments with Mt, because it was not possible to evaporate microscopic amounts of 1 0 7 Rh in form of its chloride. In addition, the temperatures of reaction and deposition are much too high for the OLGA technique that is used in heavy element chemistry, because it is limited to maximum temperatures of 500 °C.

REFERENCES

[1] P. Armbruster, On the production of heavy elements by cold fusion: The elements 106 to 109, Ann. Rev. Nucl. Part. Sei. 35, 135 (1985), chapt.4.4, p. 173.

[2] J. Merinis, G. Bouissières, Séparation par volatilisation des Radioisotopes de Mercure, Platin, Iridium, Os­mium et Rhénium formés par Spallation dans une cible d'or, Anal. Chim. Acta 25,498 (1961).

[3] B. Eichler, I. Zvára, Evaluation of the enthalpy of ad­sorption from thermochromatographical data, Radio-chim. Acta 30,233 (1982).

[4] R. Eichler, et. al., The gas phase oxide and oxyhydrox-ide chemistry of trace amounts of rhenium, Radiochim. Acta 87, 151 (1999).

127

ARE THERMOCHEMICAL DATA OF POLONIUM QUESTIONABLE?

B. Eichler (PSI)

Applying thermochemical data of elements in group 16, the standard enthalpies of gaseous monatomic polonium and its dimer have been estimated by extrapolative methods. Significant deviations to tabulated data are apparent. A Born-Haber cycle using published data shows some inconsistency. A revision of the data seems to be required.

The standard enthalpies of gaseous monatomic elements AH°A(g) are of basic importance in connection with the thermochemical description of volatilisation processes. If the volatilisation of a solid element yields the monatomic gaseous state, AH°A(g) equals the sublimation enthalpy. If elements are volatilised as dimers the dissociation enthal­pies AH°A(diss) have to be taken into account. Predictions the volatilisation and adsorption behaviour of the elements Po (with respect to the installation of Pb-Bi spallation targets), Te (as a volatile fission product), and element 116 (in connection to the gas phase chemistry of transactinide elements) are of crucial importance.

According to a well known rule in the periodic table, the metallic character of the elements increases along the groups of p-elements with increasing atomic number. These qualitative statement can be quantified as:

AH°Po(g)=0.5[AH°Po2(g)+AH°Po2(diss)] (2)

m = _ AH°A(g)-0.5-AH°A(diss)

ArTA(g) (1)

In the course of the condensation process of free atoms during desublimation processes, metallic elements form lattices with high coordination numbers. If the non metallic character dominates, the formation of dimers or polyhomo-nuclear molecules is preferred, which subsequently form solid phases. Thus, the short-range order of these dimers and molecules is often preserved in the solid phases. If the elements are not metals at all, increasing m along the groups in the periodic table represents the increase of their metallic character [1] (see Figure 1). In the groups 14, 15, and 17 linear dependencies of m as function of Z are ob­tained. For group 16 the same linear dependence can be expected. Using older published data for Te and Po [2,3] this is shown (see Figure 1, dash-dotted line). Applying more recent published data for Te [4], this rule is broken, if the old data for Po are still accepted. It can therefore be assumed that these Po data are not accurate enough. Espe­cially data obtained using 2 1 0 Po are questionable. Beside the difficulties during the handling of the highly radioactive 2 1 0 Po, the decay heat of 2 1 0 Po, the decay-caused lattice dis­tortion, and the accumulation of the decay products e.g. Pb influence the physicochemical measurements. Applying a linear relation between m and Z, according to the general rule one would deduce a value of m P o=0.541 and m E 1 1 6 =0.694. Employing AH 0 Po2(diss)=183 kJ/mol [5], from equation (1) follows a AH°Po(g)=199 kJ/mol. This value differs significantly from the published data: 143 kJ/mol [2] and 146.9 kJ/mol [3]. According to a Born-Haber cycle between the solid, gaseous dimer, and gaseous monatomic states follows equation 2:

A value of AH°Po(g)=164.25 kJ/mol is derived from equa­tion (2) applying AH°Po2(g)= 145.5 kJ/mol [3]. This value differs from the literature data too. Hence, the given tabu­lated data are not consistent. Equation (2) yields for the standard enthalpy of the gaseous Po 2: AH°Po2(g)=215 kJ/mol if the value AH°Po(g)=199 kJ/mol, estimated from equation (1) is applied. This result also differs significantly from published data. Considering sys­tematic trends of properties in the groups of the periodic table, the thermochemical calculations to the volatilisation behaviour of Po therefore require a careful critical réévalu­ation. Additionally, one should keep in mind the funda­mental importance of AH°Po(g) and AH°Po2(g) for the calculation of the stability and volatility of Po compounds as its hydride, dioxide and intermetallic molecules.

10 20 30 40 50 60 70 80 90 100 110

Fig. 1: Normalised differences between standard forma­tion enthalpies of gaseous atomic s- and p- ele­ments and the standard dissociation enthalpies of their dimers as a function of the atomic number Z.

REFERENCES

[1] B. Eichler, Kernenergie 19, 307 (1976).

[2] G. A. Krestov, Radiokhimiya 4, 690 (1962).

[3] V. P. Glushko, Thermal constants of substances, Vol. II, Moscow 1966.

[4] A . . Efimov, Svoistva neorganicheskikh sojedinenii, Izd. Khimiya, Leningrad 1983.

[5] G. V Samsonov, Svoistva elementov, Izd. Metallurgiya, Moskva 1976.

128

ACCOMMODATION COEFFICIENT OF HOBr ON DELIQUESCENT SODIUM BROMIDE AEROSOL PARTICLES

M. Wachsmuth (PSI), H. W. Gäggeler (Univ. Bern &PSI), R. von Glasow (MPI-CHMainz), M. Ammann (PSI)

Experiments using the short-lived isotopes 86Br and 84Br to measure the uptake of HOBr on deliquescent NaBr particles were analysed. From the data, an accommodation coefficient of0.6±O.2 was derived. The effect of this high accommodation coefficient on the chemistry of the marine boundary layer compared to previous estimates was assessed using the box model MOCCA.

INTRODUCTION

The heterogeneous reaction of bromine compounds with sea-salt bromide belongs to the key processes sustaining near surface ozone depletion events in the arctic at polar sunrise [1]. The reaction of HOBr with bromide, HOBr + B r + H + -> Br 2 + H 2 0 (1) leads to an efficient release of bromine from sea salt exposed to the air. Data about this reaction within sea-salt aerosol particles are scarce [2]. Under conditions where this reaction is fast, the uptake of HOBr to the aerosol is limited by the (mass) accommodation coefficient, a, which is the probability that a gas kinetic collision of a molecule results in solvation at the surface of an aqueous droplet. The aim of the present work was to investigate the HOBr(g) - aerosol bromide interaction at extremely low concentrations using the short­lived bromine isotopes 8 6 Br and 8 4 Br available from the gas-jet facility at SINQ [3].

F L O W REACTOR EXPERIMENTS

The experimental set-up is described in detail elsewhere [4]. Briefly, HOBr labelled with 8 6 Br and 8 4 Br was mixed with the deliquescent NaBr aerosol particles in a flow reactor. At the end of the flow tube, HOBr(g) and Br2(g) were separated from the particles using diffusion denuders and a filter. To both, denuders and filter, a y-detector was attached to get the number of labelled HOBr(g) and Br2(g) molecules, and the bromine activity associated with the particles. The primary product of reaction (1) is labelled Br2(aq). However, due to the very fast equilibrium with Br 3

_(aq), the isotopes rapidly exchange with bromide, finally leading to bromine isotopes associated with bromide in the aerosol phase observed on the filter. Fig. 1 shows activity associated with unreacted HOBr(g) and with particulate bromide as a function of the reaction time in the flow tube. The first order loss rate of HOBr(g) derived from these data was translated into an uptake coefficient by correcting for diffusion (see ref. 4 for details). The uptake coefficient was parameterised according to

1 _1 | 1 _1 | V

Tup, a rrXn

a 4HRT<JkiD,

where H is the Henry's Law coefficient, ki and Di the first order loss rate and the diffusion coefficient in the liquid phase, respectively, R the gas constant, and T the temperature. In these experiments, due to the very high bromide concentration and the very low HOBr(g) concentration (300 molecules per cm 3!), the first order loss rate was very high. At maximum, one HOBr molecule was

taken up per particle, so that also the H+ concentration became never Hmiting. Therefore, the uptake coefficient was purely limited by the accommodation coefficient. A best fit to the data resulted in a value of a=0.6±0.2.

This value is a factor of 10 higher than estimates used in previous model calculations. We therefore used the box model MOCCA [5] of the marine boundary layer to assess the effect of this higher accommodation coefficient on the halogen cycling. The model was run for two different scenarios, one with high bromine release and one for moderate bromine release from the sea salt aerosol. Although the initial increase of gas-phase bromine is stronger, only in the latter scenario a long-term effect on the bromine partitioning was observed. The net effect on the ozone loss was insignificant in both cases. However, a significant effect on the release of chlorine was seen, mainly due to the reaction of HOBr with chloride and release of BrCl, analogous to reaction (1).

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0

Reaction time [s]

Fig. 1: Fraction of bromine activity associated with HOBr(g) (squares) and with aerosol phase bromide (triangles). The Unes represent mass transfer calculations for a=0.6 (best fit, thick Unes) and for a=0.3 and a=1.0 (thin lines).

REFERENCES [1] R. Vogt et al., Nature 383, 327 (1996). [2] J.P.D. Abbatt, G.C.G. Waschewsky,

J. Phys. Chem. A 102, 3719 (1998). [3] M. Wachsmuth et al.,

Radiochim. Acta, 88, 873 (2000). [4] M. Wachsmuth et al.,

Atmos. Chem. Phys. Discuss.l, 439 (2001). [5] http://www.mpch-mainz.mpg.de/~sander/mocca

129

UPTAKE OF H N O 3 TO DELIQUESCENT SEA SALT PARTICLES

C. Guimbaud, F. Arens, L. Gutzwiller, E. Rössler, M. Ammann (PSI)

The uptake coefficient of HNO3 on deliquescent sea-salt particles is measured (yupt = 0.50 ±0.20). The chemical aspect of the reaction is discussed via the thermodynamic equilibrium North American Aerosol Inorganics Model

Sea-salt aerosol plays an important role on the removal pathway of nitrogen oxides in the marine troposphere via the acid-displacement:

HN0 3 (g) + NaCl(s,aq) -> NaN0 3(s,aq) + HCl(g), and affects the chemistry of the troposphere over large areas of the world.

HNO3 labelled with the short lived radioactive isotope 1 3 N is mixed with deliquescent sea-salt particles in gas suspension in a flow reactor (RH=55% and P=760 torr) [1, 2]. The uptake coefficient (yupt) is derived from the loss of gas phase H N 0 3 and the gain of particulate nitrate as a function of reaction time [3]. The experiments are performed with small particles (-70 nm diameter), so that diffusion does not strongly affect the mass transfer. The effect of the H N 0 3 gas phase concentration on the measured y u p t and the chemical process occurring after the uptake are both investigated via the North American Aerosol Inorganics Model (AIM) which predicts the distribution of H 2 0 , H N 0 3 , and HCl in the gas phase and aqueous phase (as ions for strong acids and salts), at equilibrium, for a NaCl/HN0 3 /H 2 0 system [4].

An average value for y u p t of 0.50 ± 0.20 is derived from measurements performed at 2, 9, and 57 ppbv of H N 0 3

concentration (Figure 1), as no dependence with reaction time is observed. However, at higher H N 0 3 concentration (575 ppbv), the drop of y u p t with reaction time is significant (Figure 2). This drop is concomitant with (i) an equilibrium which is reached between uptake and release of H N 0 3

(Figures 1 and 2) and (ii) a limitation due to the fact that almost all CI ions from the aqueous phase are displaced to the gas phase as HCl (as shown by the AIM model in Figure 3).

10 100 HNO,, ppbv

Fig. 1: Average uptake coefficients (plain diamonds) as a function of H N 0 3 concentration. H N 0 3 taken up observed for a representative reaction time of Is in the flow reactor (empty triangles) are compared to H N 0 3 in the aerosol phase predicted at equilibrium (empty squares) derived from the AIM model.

1 0 0

0 . 6 0 . 9 1 . 2

Reaction time, s

Fig. 2: H N 0 3 y u p t (plain diamonds) as a function of reac­tion time, at 575 ppbv initial H N 0 3 concentration. H N 0 3 in the aerosol phase observed (empty trian­gles) and predicted at equilibrium (41 ppbv, hori­zontal line) are represented. The difference be­tween the apparently observed equilibrium and the calculated one is due to an under-estimation of NaCl concentration, as particles were not assumed to be supersaturated in the AIM model.

1 . 0

c a>

I 0.8

f 0.6 o

I 0 . 4

c o •g 0.2 2 LL

0.0

\ HNO^G)

H, N0 3 = CI

! \ H*(aq)

1 • • • , HCKGT ' - S r - .

0.1 1 10 100 1000 H and N0 3 inputs (ppbv)

Fig. 3 : Simulated distribution of the hydrogen burden for a NaCl-H 2 0-HN0 3 system representative of our aerosol experiment, at equilibrium, and as a func­tion of H and N 0 3 inputs (representing in the AIM model H N 0 3 gas phase concentration before up­take). The 39.2 ppbv input (vertical dashed line) corresponds also to the total amount of CI present in the system, assuming saturated sea-salt aerosols.

REFERENCES

[1] M. Ammann, Radiochim. Acta, in press (2001).

[2] M. Kalberer et al., J.G.R. 104,13825 (1999).

[3] C. Guimbaud et al., in preparation for Atmos. Chem. Phys. (2002).

[4] S.L. Clegg et al., J. Phys. Chem. A 102, 2155 (1998).

130

AQUEOUS PHASE KINETICS OF N 0 2 WITH RESORCINOL AND DIHYDROXY-NAPHTHALENE

L. Gutzwiller, E. Rössler, M. Ammann (PSI)

The liquid phase kinetics of two OH-substituted aromatics as proxies of atmospheric SVOCs with N02 have been investigated in a wetted wall flow tube in the range pH=3 to 9. The rate constant obtained for resorcinol is an order of magnitude lower compared to another study at constant, but higher pH.

Resorcinol (Res) has been observed in emissions from wood combustion [1] and as product from photooxidation of benzene, and dihydroxy-naphthalene (Np(OH)2) may be expected as intermediate in the oxidation of naphthalene, one of the most abundant polycyclic aromatic hydrocarbons (PAH) in the atmosphere [2]. Due to their OH functionalities both these substances are expected to reduce N 0 2 to nitrous acid (HONO), which might be an important precursor in photochemical ozone formation [3].

The uptake of N 0 2 by aqueous solutions of Res and Np(OH) 2 have been assessed using a wetted wall flow tube [4]. Buffered solutions of these compounds in the range of 10"5 to 1M and pH=2.6 to 9 were injected at the top of a sand-blasted glass tube of 12 mm i.d., so that a homogeneous film was formed flowing down on the inner tube walls. A N 0 2 / N 2 gas flow of 350 ml/min was passed through the tube and its residence time varied by extracting the gas at four different heights. The N 0 2 loss in the extracted gas was monitored using a chemiluminescence detector.

1.00E-04

1.00E-05

1.00E-06

1.00E-07

• 10(-4) M • 10(-3)M A10( -2) M X 1 0 ( - 1 ) M O l M

O

X

o

X

° A •

X * • • _ m •

4 6

pH

10

Fig. 1: Uptake of N 0 2 into aqueous solutions of Res over the range of pH 2.6 to 9. The symbols correspond to different liquid phase concentrations. The N 0 2

gas phase concentration was around 80 ppb.

Figure 1 shows the uptake coefficient Yuptake corrected for gas phase diffusion. Clearly, the uptake increases as a function of pH and Res concentration since towards higher pH more Res is deprotonated and may reduce N 0 2 to nitrite according to the following scheme:

ArOH + N 0 2

Aro - + N 0 2

=> Products (1)

=> ArO* + N O / (2)

where ArO" stands for a deprotonated OH-substituted aromatic compound ArOH like Res or Np(OH) 2. For a given pKa, the degree of deprotonation a may be calculated according to the formula by Henderson-Haselbalch so that

the second order rate constant kr for the reaction of N 0 2

with ArOH may be written as:

kr = (1-a) k¡ + a k 2

Figure 2 shows kr as a function of pH for the case of Res. Since one of the reaction partners, namely N 0 2 , is constantly supplied from the gas phase, the kinetics have to be checked for liquid phase diffusion limitation. In fact, if the kinetics is fast, N 0 2 is reacted quickly and a concentration gradient across the liquid film occurs. Both, a diffusion limited and a non-diffusion limited case, have been tested, and it could be shown that the reaction is diffusion limited.

1.00E+02 0.00 2.00 4.00 6.00 8.00 10.00

PH

Fig. 2: Second order rate constant kr for Res as a function of pH. The fit corresponds to k 2= 3.2-10 7 M ' V 1

a n d k 1 = 100 M V .

The rate constant k 2= 3.2-10 7 M ' V 1 for Res is roughly a factor of ten smaller than the one determined at a constant pH of 12.2-12.4 by Alfassi et al. [5]. Similarly to Res, the rate constants for Np(OH) 2 were determined amounting to k 2= 4-10 7 M's"1 and k 1 = 1000 M's"1 for which no literature values are available.

REFERENCES [1] P. M. Fine, G. R. Cass, B.R.T. Simoneit,

Environ. Sei. Technol., 35, 2665 (2001). [2] J. N. Bunce, L. Liu, J. Zhu,

Environ. Sei. Technol. 31, 2252 (1997). [3] M. E. Jenkin, R. A. Cox, D. J. Wilhams,

Atmos. Environ. 22, 487 (1988). [4] Ch. George, J. L. Ponche, Ph. Mirabel, W. Benke,

V. Scheer, C. Zetzsch, J. Phys. Chem. 98, 8780 (1994).

[5] Z. B. Alfassi, R. E. Huie, P. Neta, J. Phys. Chem. 90, 4156 (1986).

131

UPTAKE OF N 0 2 ON RESORCINOL AND SUBSEQUENT HONO FORMATION

L. Gutzwiller, E. Rössler, M. Ammann (PSI)

The heterogeneous HONO formation on solid Resorcinol coatings is explored qualitatively. The reactive uptake of NO2 at a relative humidity close to deliquescence (80% RH) is in agreement with liquid phase experiments and amounts to about 10'6.

Resorcinol has been observed in emissions from wood combustion [1] and as product from photooxidation of benzene. Due to its OH functionalities this substance is expected to reduce N 0 2 to nitrous acid (HONO), which might be an important precursor in photochemical ozone formation [2].

The uptake of N 0 2 by aqueous solutions of resorcinol has been assessed in the preceeding report. The heterogeneous HONO formation, especially by OH substituted aromatic compounds, is known/expected to be humidity dependent [3]. Therefore, the goal of this study was to investigate the HONO formation in the transition regime when passing from a liquid (aqueous) film to a "dry" solid surface. Essentially two types of coatings were prepared on glass tubes: a) 0.6 ml of 0.1 M resorcinol solution with Triton for good wettability was deposited on the inside of a glass tube and dried carefully using nitrogen so that the resorcinol crystallized evenly over the whole tube length of 40 cm; this coating corresponds to about 50 monolayers of resorcinol. b) a saturated solution of resorcinol was given on the tube and also dried using nitrogen. The tube was then further dried during one hour in an oven at 80°C in order to get rid of crystal water. The tubes were then exposed to a N 0 2 / N 2 flow at atmospheric pressure and the gas phase HONO and NO x concentrations measured at the tube exit using a wetted wall flow tube [4] and a NO x

analyser.

Fig. 1: Uptake of N 0 2 on a thin layer of resorcinol and subsequent HONO formation. The dots (right axis) and the triangles (left axis) correspond to the N 0 2

and HONO concentration, respectively.

Fig. 1 shows such an experiment in which a resorcinol layer prepared according to procedure a) was exposed to 1250 ppb N 0 2 starting at t = 160 min. The HONO concentration increases instantaneously to 230 ppb before dropping to a steady state at which 100 ppb of N 0 2 are quantitatively reacted to HONO. Integrating the exponential decay of the HONO signal up to steady state amounts to 3.5-10 1 6 HONO

molecules or 1 .410 1 4 HONO per cm . This corresponds to approximately half a monolayer of pure resorcinol.

Fig. 2 shows the humidity dependence of the HONO for­mation on resorcinol prepared according to procedure b) and expressed as the fraction of reactive N 0 2 collisions y^ . For the exposure to both low and high N 0 2 concentrations, the HONO formation increases exponentially in the range of 20% RH up to deliquescence at around 85% RH. Over the same humidity range, the reactive uptake increases from less than 10"7 to approximately 10"6. The last value is in agreement with the uptake of N 0 2 into an aqueous solution of resorcinol at pH=6 (see preceeding report). If the satu­rated solution of resorcinol is only dried in N 2 but not an­nealed at 80°C, the N 0 2 uptake is much larger but the HONO formation is accompanied by a significant amount of NO. In this case, HONO probably remains partially on the surface and is subject to further reaction. Clearly, the reaction probability is smaller for higher N 0 2 concentra­tions, which might be due to a Langmuir-Hinshelwood type mechanism as observed on solid anthracenetriol [3].

3.00E-07

2.50E-07

2.00E-07

S Z

f 1.50E-07-

4

1.00E-07

5.00E-08

0.00E+00

I F F * '

6.00E-07

5.00E-07

4.00E-07

• 3.00E-07

• 2.00E-07

1.00E-07

0.00E+00 20 40 60 80

relative humidity 100

Fig. 2: HONO formation as a function of relative humi­dity and N 0 2 concentration resorcinol prepared ac­cording to b). The dark diamonds (left axis) and open triangles (right axes) correspond to 570 and 25 ppb N 0 2 , respectively.

REFERENCES [1] P. M. Fine, G. R. Cass, B. R. T. Simoneit,

Environ. Sei. Technol. 35, 2665 (2001). [2] M. E. Jenkin, R. A.Cox, and D.J. Wilhams,

Atmos. Environ. 22, 487 (1988). [3] F. Arens, L.Gutzwiller, H. W. Gäggeler, M. Ammann,

in preparation for Phys. Chem. Chem. Phys. (2002). [4] L. Gutzwiller, F. Arens, U. Baltensperger,

H.W. Gäggeler and M. Ammann, Environ. Sei. Technol., in press (2002).

132

THE ADSORPTION OF NITROGEN OXIDES ON ICE

T. Bartels (PSI), H. W. Gäggeler (Univ. Bern & PSI), M. Ammann (PSI)

Thermo-chromatography is a well-known method to evaluate the standard adsorption enthalpy. It is based on the assumption that the adsorption equilibrium determines the retention of any species in a chromatographic column. It is shown here that this assumption is valid for the thermo chromatography process of nitrogen oxides labelled with the short-lived radioactive isotope 13N on ice surfaces at ppb levels and that the migration process is not influenced by a quasi liquid layer, grain boundaries, reaction or dimerisation.

Thermo-chromatography is a gas - solid chromatography method, well suited to analyse the adsorption properties of gases, e.g. nitrogen oxides, metals and heavy elements on various surfaces, such as metals or even ice [1]. In principle, a strong temperature gradient of - 8 K per centimetre is established along a column filled with ice spheres, as can be seen in figure 1 for an experiment using 1 3 N to label nitrogen oxides of up to 50 ppb in the gas phase. The temperature gradient leads to an enhanced retention of the species as they are transported along the column. After a certain time the migration distance of each species in the column is determined, and based on those findings and the assumption of adsorption being the step determining retention, a standard adsorption enthalpy is calculated.

Column Length [cm]

Fig. 1: Chromatogram (bars) and temperature gradient (dots) in a typical thermo-chromatography experiment. Shown is the distribution of 1 3 N along the column. The column entrance is at the right side of the picture, the first peak is PAN, the second N 0 2 .

The first question that has to be answered is the specification of the nitrogen oxides, as dimerisation of e.g. N 0 2 or reaction of NO with N 0 2 forming N 2 0 3 , are thermodynamically favoured (Fig. 2). Briefly, transport of the nitrogen oxides to the cold part of the column is much faster than dimerisation in the gas phase, which makes this reaction unlikely to occur under the non-steady-state conditions of the chromatographic process. At a certain temperature in the colder part of the column, adsorption rapidly increases, leading to an enhanced retention in the column and an accumulation of N 0 2 > mainly on the surface. The formation of N 2 0 4 on the surface can be ruled out, because it would lead to a fronting of the peak due to the stronger ice interaction of N 2 0 4

compared to N 0 2 , which was not observed in our experiments. The same holds for formation of N 2 0 3 .

NOy (react) NOy (gas) 1=*. NOy (dim)

NOy(qll) NOy (ads) ——Ë NOy (aq) 1=*. NOy (diss)

It It • NOy (bulk) i=s. NOy(gb)

Fig. 2: Overview of equilibria of nitrogen oxides in the gas and ice phase, such as dimerisation (dim); solvation into the quasi-liquid layer (qll), bulk or grain boundaries (gb); adsorption (ads); building of a hydrate cover (aq); and dissociation.

Secondly, the retention in the column could be influenced by various equilibria (Fig. 2), and the question arises which one, or which combination of them, determines the retention. The equilibria directly following the adsorption step (solvation in a quasi-liquid layer, formation of a hydrate cave and even dissociation) are known to be much faster than the adsorption equihbrium. Thus the adsorption equilibrium can evolve unhindered, and in addition is the hmiting, and thus retention determining, factor in the overall transport of each species along the column. On the other hand, diffusion into the bulk or along the grain boundaries are extremely slow processes, thus very unlikely to happen during the short residence time of the adsorbed species on the surface. And even if they occur, due to the strong concentration gradient and the slow speed, both equilibria would have to be regarded as irreversible and thus would not influence the adsorption equilibrium.

Thus we are convinced that adsorption exclusively determines the retention of nitrogen oxides, and the thermo-chromatography is well suited to analyse the adsorption of complex systems as NO y on ice using 1 3 N as tracer in a non-carrier free environment.

ACKNOWLEDGEMENT

The authors would like to thank B. Eichler for his valuable advice. This work forms part of the EU project CUT-ICE funded by the Swiss Federal Office for Education and Science.

REFERENCES

[1] B. Eichler et al., J. Phys. Chem. A 104, 3126 (2000).

[2] T. Bartels et al., Atmospheric Chemistry and Physics, in preparation (2002).

133

ENTROPY CALCULATIONS OF THE ADSORPTION PROCESS FOR NO

T. Bartels (PSI), H. W. Gäggeler ( Unv.i Bern & PSI), M. Ammann (PSI)

Thermo-chromatography is a well suited method to evaluate the adsorption behaviour of gases on various surfaces. To analyse the data, the adsorption entropy has to be calculated. It is shown how the choice of standard states influences the resulting equilibrium constant. Extrapolations of the partition coefficient to atmospheric conditions and the standard adsorption enthalpies are given for adsorption of NO on ice.

To calculate the adsorption enthalpy based on our experimental findings of a thermo-chromatography experiment, we do need to input the entropy change connected with adsorption [1].

This value can be very precisely calculated for ideal atoms based on statistical thermodynamics as the difference of the absolute entropy of the particle in the gas phase and the entropy of the adsorbed particle.

Here, the entropy of the free particle is calculated based on the particle in the box, which has 3 translational degrees of freedom. The adsorbed particle has lost the translational degree of freedom perpendicular to the adsorbent surface and has gained one vibrational degree of freedom in that direction. The vibrating frequency is set equal to the phonon frequency of the ice surface for our calculations. Electronic and vibrational degrees of freedom are regarded to stay identical in both states and thus cancel out in the resulting formula. The rotational degrees of freedom are certainly reduced from a free rotation in the gas phase to a hindered one after the adsorption. How strong the rotation is hindered in the adsorbed state is hard to estimate, but as at 100 - 200 K even the free rotation contributes only little (~30 %) to the total entropy of the free particle, as can be seen in table 1, we neglect its contribution to the adsorption entropy, which in any case would not exceed 1.5 kJ/mol or 6 %. The resulting formula to calculate the adsorption entropy can be seen in eq. 1.

Table 1: The contribution of the translational, rotational, vibrational and electronical degrees of freedom to the absolute entropy for a NO molecule in the gas phase

T Str srot Svib Se [K] [J/K mol] [J/K mol] [J/K mol] [J/K mol]

100 128.5 39.2 0.0 0.0

200 142.8 44.9 0.0 0.0

m -k„-T, 1

— + -2

ft -v h-v

Equation 1: Calculation of the adsorption entropy. A/V is the standard area to standard volume, T A is the experimental adsorption temperature, v is the phonon frequency of the ice surface.

The absolute value of the standard adsorption entropy depends on the choice of standard states (A/V), which is evident as the entropy of the particle in the box depends on the box size. For adsorption processes no well-defined standard state has been introduced as for gas phase processes (1 bar, 0 °C). In the literature, two different definitions can be found. Eichler et al. set the ratio of A/V to 1 cm"1 [1]. The second standard of 3x l0 6 for A/V is used by Goss et al. [2,3]. The idea of this standard state is to treat the adsorbed molecules as a two dimensional gas and define a standard pressure and temperature, at which the particles on the surface have the same average distance to each other as the particles in the ideal gas at standard conditions. This leads to a standard two-dimensional pressure of 3.4xl0"2 Pa m at 0 °C and a standard area of 6.72xl0 6 m 2. This standard area and the standard gas volume (22.4 1) result in the second standard state used here. As is evident from Table 2, both standard states yield different standard adsorption entropies and equilibrium constants (KP). Nevertheless both of these yield identical adsorption enthalpies, as expected because the entropy does per definition not depend on standard states, and the same partition coefficient (K;) at conditions present in cirrus clouds. See equation 2 for definitions of K¡ and Ka.

Table 2: Standard adsorption enthalpy, entropy and equi­librium constant, as well a partition coefficient extrapolated to conditions present in contrails (T=-60 °C, a/v = 8 cm 2/cm 3) for NO on ice.

A/V = 1 cm"1 A/V = 3 10s crn 1

AS°a(|s - 164J/molK - 40 J/mol K

AH° a i s - 20 kJ/mol -20 kJ/mol

K„ 2.2 10" 6.5 102

Kj (contrails) 1.7 10"3 1.7 10"3

£ _ nads n

Sas K

K p - I 0 PIP v A

Equation 2: Partition coefficient (K¡) and adsorption equilibrium constant (KP) with f: two dimensional pressure, f°: two dimensional standard pressure, p: pressure, p°: standard pressure, a/v: area to volume, A/V standard area to standard volume

REFERENCES [1] B. Eichler, Radiochimica Acta 30, 233 (1982). [2] K.U. Goss, Environ. Sei. Technol. 31, 3600 (1997). [3] de Boer, The Dynamical Character of Adsorption,

(Clarendon press, Oxford 1968).

134

PROTRAC - PRODUCTION OF TRACERS FOR ATMOSPHERIC CHEMISTRY

M. Ammann, P. Ming, M. Birrer, J. Jegge, A. Isenschmid (PSI)

The aim of PROTRAC is to provide the short-lived radioactive isotopes 13N, nC and 150 to our chemistry laboratories as tracers for experiments pertaining to atmospheric chemistry. It uses a new target installed at the isotope production station IP-2 and new transport line for on-line transport of these isotopes in the gas-phase

1 OVERVIEW

The new installations are based on the existing infrastruc­ture of the isotope production station IP-2 to irradiate dif­ferent targets with either 72 or 40MeV protons. For PROTRAC, the target design follows the design of the existing gas target for production of U C for radiopharma­ceutical applications.

2 TARGET

The target design was adapted according to our experiences with a similar set-up at the low energy beam-line at the Philips Cyclotron for the production of the short-lived iso­tope 1 3 N [1]. The first difference to the standard targets at IP-2 is that it is operated in on-line mode, i.e., the carrier gas passes the target continuously for delivery of isotopes to the laboratory. Second, the irradiated volume (see Fig. 1) is formed by a hollow quartz cone to provide a surface as inert as possible to chemically reactive species formed under the influence of radiation chemistry. Third, a thermal converter is attached to the main body of the target to allow for chemically converting highly oxidised nitrogen species to nitrogen monoxide, an important feature when the short­lived isotope 1 3 N needs to be transported over long-dis­tances through capillaries. The window design was opti­mised for production of 1 3 N with 10 to 15 MeV protons.

graphite converter

quartz cone

j j , gas out

cooling water

entrance window

gas in

it to up to three independent experiments is controlled by mass flow controllers in the laboratory.

For security, the PVDF capillaries are further contained in a 32mm inner diameter Polyethylen tube. This outer tube is continuously flushed with nitrogen and kept 50mbar below ambient pressure using a membrane pump, the exhaust of which is passing an activated charcoal trap. At this trap, an activity monitor checks for activity in case of leaks or bro­ken connectors along the flow system.

On October 16 t h and November 29 t h , the target and the transport lines were tested with lOuA protons using the reaction 1 6 0(p,a) 1 3 N (40mb at 10-15 MeV) to produce 1 3 N with a half-life of 10 min. The carrier gas (He) contained 20% 0 2 at a pressure of 2 bar and a flow of 1 Normliters per minute. Under these conditions it was expected that the primary 1 3 N species formed would be H 1 3 N 0 3 , which could then be reduced to 1 3 NO in the converter tube attached to the target and filled with graphite. The test irradiations clearly showed that the converter temperature is critical for having a high conversion rate. A fraction of the gas obtained in the laboratory was accumulated on a Co oxide trap, and the half-life observed of 10 min confirmed the identity of 1 3 N. Fig. 2 shows a record of the delivery rate of 1 3 N measured in the laboratory during the irradiation on November 29 t h . The overall yield was 10 to 20% based on the cross section and the proton current.

3.5E+07

3.0E+07 C

§ 2.5E+07

S. 2.0E+07

ÏÏ 1.5E+07 o

2 1.0E+07 2

5.0E+06

0.0E+00

A A

/ / V

/ 14:00:00 14:15:00 14:30:00 14:45:00 15:00:00

rime on November 29

Fig. 2: Record of 1 3 N delivery rate to the laboratory during a test irradiation of the PROTRAC target.

Fig. 1: PROTRAC Target prepared for the production of

3 TRANSPORT LINE

The transport line consists of three (one for use, two spare) Polyvinylidenfluoride (PVDF) tubes with 4mm inner diameter. The capillary in use is kept at a pressure of typi­cally 2 to 5 bar. In the laboratory, it passes a GM probe to monitor the activity contained in it. The total gas flow through the capillary and the addition of small fractions of

ACKNOWLEDGEMENTS

We greatly appreciate the continuous support by H. Kum­mer, W. Fichte, Y. Eichholzer, P. Wenger, E. Gisel, J. Paulke, W. Bulgheroni, S. Staudenmann, I. Jirousek, G. Dzieglewski, H.W. Reist, A. Mezger and his operating team.

REFERENCE

[1] M. Ammann, Radiochimica Acta, in press (2001).

135

DEVELOPMENT OF A CHEMICAL IONISATION MASS SPECTROMETER

C. Guimbaud, M. Birr er, D. Piguet, M. Ammann (PSI)

This instrument uses the properties of ion-molecule reactions to measure atmospheric species of interest at ppb level, and aims to complement the radiochemical tracer technique to study atmospheric processes on aerosol particles.

INTRODUCTION Chemical Ionisation Mass Spectrometry (CIMS) has been widely used for real time detection of atmospheric species at ppb level [1,2]. An Atmospheric Pressure Chemical Ionization (APCI) quadrupole mass spectrometer is under development for trace gas analysis, as complement to the current analytical technique available at PSI using radioactive tracers ( 1 3 N, U C and 8 4Br) for species such as HN0 3 , acetone, and HOBr.

THE CEVIS TECHNIQUE Chemical ionization uses ion molecule reactions, taking place at thermal energy in a buffer gas (1 and 760 torr). Thus, high selectivity and sensitivity can be achieved from the choice of the reactant ion, by opposition to more conventional mass spectrometers based on electron impact ionization which results in fragment ions. The chemical ionization processes described bellow will be developed for the detection of compounds of atmospheric interest: (a) Proton transfer reaction mass spectrometry (PTRMS) [1] will be used for the detection of organic species R such as NMHCs (Non Methane HydroCarbons) and OVOCs (Oxygenated Volatile Organic Compounds), which have higher proton affinity than H 2 0 , according to

H + ( H 2 0 ) n + R -» RH + (H 2 0) n . ! + H 2 0 n > 1. PTRMS allows for high efficiency detection of acetone [1], methyl peroxy radical [3], and possibly PAN [4]. (b) Inorganic compounds will be detected with SF6" [2], as they often have higher electron affinity than SF 6. More specifically, N 0 2 and HNO3, can be selectivity monitored as the product ion N0 2 " and N03"(HF), respectively. However, N0 2 " may be more suitable to transfer its charge to highly electro-negative species without fragmentations, such as halogen inorganic species. (c) Negative APCI via the reaction of 0 2" has been found to be efficient for the detection of Cl 2 [5], BrCl and Br 2 [6] by charge transfer and for the detection of HOC1 by formation of the adduct HOC1.02" [7]. Therefore, negative APCI could be suitable for measurement of HOBr, a species of interest in the marine boundary layer.

THE MASS SPECTROMETER The instrument is composed of a CI region (operating pressure of 10 or 760 torr, depending of the sampling cone hole size) and of a set of electrostatic lenses to focus ions through an intermediate pressure chamber and to the quadrupole mass filter (Fig. 1). The quadrupole mass spectrometer (ABB extrel Merlin) is equipped with a cross beam deflector ionizer yielding a compact vacuum system with efficient pumping on both stages and a significant signal-to-noise ratio improvement compared to on axis quadrupole systems [8].

N2 + R,0(ppnw) 5 L min

CI Intermediate région pumping stage

TÚOtorr 1 0 s torr 0 V »• -Ü «•

/////

-/ ' L J > Glow ^ I p

Tungsten needdle + 3 k V discharge

Turbo pump

to detector

Quadrupole filter

Le ises ~~ n u » • Turbo

pump

MS pumping stage Q>™l™P°k 10 torr deflector

Fig. 1: The mass spectrometer equipped with an APCI ion source (corona discharge). The reaction distance and time are about 2 cm and 10 ms, respectively.

H 3 0 * ( H 2 0 ) H * ( C H j C O C H j )

H j O ' d l j O ) !

H j O *

—A-C H j C O *

H ^ H j O H C H j C O C H j )

H j O ' f H j O l j j\

10 20 30 40 50 60 70 80 m/z

Fig. 2: PTRMS of acetone at atmospheric pressure. The dashed spectrum represents the water clusters observed. The full Une spectrum is obtained by adding acetone in the buffer gas (= 2 to 5 ppbv).

ACKNOWLEDGEMENTS The ion source housing, the ion molecule reactor and the interface flange to the MS were constructed by A. Tiefenauer and M. Lehnherr, under supervision of S. Forss, Ch. Zumbach, and P. Kramer.

REFERENCES [1] W. Lindinger et al., Int. J. Mass Spectrom. Ion

Processes 173,191 (1998). [2] L. G. Huey, J. Phys. Chem. 99, 5001 (1995). [3] K. W. Scholtens et al.,

J. Phys. Chem. 103,4378 (1999). [4] N. Srinivasan et al.,

Rapid Commun. Mass Spectrom. 12, 328 (1998). [5] C. W. Spicer et al., Nature 394, 353 (1998). [6] K. L. Foster et al., Science 291,471 (2001). [7] K. L. Foster et al.,

Phys. Chem. Chem. Phys. 24, 5615 (1999). [8] R. E. Pedder, Extrel appUcation Notes

RA_1201C (1996) and RA_1203C (1997).

136

PRELIMINARY RESULTS FROM GLACIO-CHEMICAL INVESTIGATION OF AN ICE CORE FROM BELUKHA GLACIER, SIBERIAN ALTAI

S. Olivier (Univ. Bern & PSI), M. Schwikowski, B. Rufibach (PSI), H.W. Gäggeler, P. Ginot (Univ. Bern & PSI), M. Lüthi (VAW), T. Papina, S. Eyrik (IWEP), M. Saurer, S. Bajo, J. Eikenberg (PSI)

In July 2001, a 140-meter deep ice core was recovered from the Belukha glacier in the Siberian Altai. First results indicate that the glaciochemical record is preserved, despite of surface melt features, and that the accumulation rate is only about 0.5 m weq per year.

The Altai mountain region is located close to major sources of air pollution in East Kazakhstan and South Siberia (heavy metal mining, metallurgy) as well as to the nuclear test site of Semipalatinsk (release of radionuclides into the atmosphere). In order to reconstruct air pollution levels in the Altai region, a 140 m ice core was drilled during a two-weeks campaign on the Belukha glacier (49°48'26.3"N, 86°34'42.8"E, 4062 m asl). This glacier is located on a saddle between the two summits of the Belukha, the highest mountain in the Altai (4506 m asl). This site was selected based on the results of an exploratory study conducted in 2000 [1]. The drilling nearly reached bedrock, as indicated by the glacier thickness measurements [2]. The 900 kg of collected ice were transported in frozen conditions (cooled with dry ice) to Switzerland for glaciochemical analyses. In addition, six soil samples and a lake sediment sample were collected near the Ak-kem basecamp at about 2100 m asl. Up to now, the 10 topmost meters of the ice core were cut into 5 cm samples, following the decontamination proce­dure described in [3]. Concentrations of major ionic species were determined by ion chromatography, pH by a pH-elec-trode and the stable isotope ratios 6 1 8 0 and ÖD by isotope ratio-mass spectrometry. In this segment, several ice layers with a maximum thickness of 30 cm were observed, sug­gesting that surface melting and subsequent refreezing might have occurred during warm summer periods. During the drilling campaign, air temperature was measured every 30 min. by an automatic weather station installed on the glacier. Average temperatures were during the day - 4 ± 3°C (l<y) and during the night - 5 ± 3°C (max: 2°C, min: -11°C), indicating that occasionally temperatures are high enough to induce surface melting. Eventually formed sur­face melt water should refreeze in the cold firn underneath (see borehole temperature profile in [2]). This assumption is supported by both the stable isotope record and the concen­trations of the major ionic species, showing discernible fluctuations (Fig. 1). Thus, the glaciochemical record seems to be preserved and not significantly altered by melting processes.

0.1 0 .9 1.8 2 .5 3 .2 4 .1 4 .8 5 .6 6.4 7.2 8 .0 8 .7

D e p t h [ m w e q . ]

Fig. 1: Variation of 6 1 8 0 and ÖD in the upper 10 m of the Belukha ice core.

Similarities with the ÖD record from the shallow firn core

taken in summer 2000 on the Belukha west plateau (49°48'49"N, 86°32'29"E, 3895 m asl) [1] suggest that the accumulation at the drilling site between July 2000 and July 2001 was less than about 0.5 m weq. (Fig. 2). Preliminary tritium analysis hint to a similar net accumulation. The average annual precipitation over the last 10 years at the Ak-kem meteorological station amounts to 0.56 m. This indicates that snow at the Belukha glacier might be partly eroded by wind, a condition typical for a glacier saddle where wind speeds are increased. Strong winter minima are missing in the 6D record (e.g. the -169.1 %c minimum seen in the record from the west plateau), possibly due to small amounts of precipitation in winter or due to wind erosion.

Delta_D 2001

Fig. 2: ÖD record from the west plateau (upper panel) and from the Belukha saddle (lower panel).

The bulk activity input of the radionuclides 1 3 7 Cs, 2 3 2 Th, 2 3 8 , 2 3 9 + 2 4 0 ^ 2 3 8 ^ d e t e r m i n e d b y y . ^ a . s p e c .

trometry in two of the six soil samples. Contrary to expec­tations, the obtained values (activity and Cs/Pu ratio) are comparable to those observed in Swiss soils. ACKNOWLEDGEMENTS We thank Andrea Bosshard and Walter Fetscherin, Swiss Ambassador in Russia, for the support, Nestlé, Russia, for sponsoring the expedition food, Altaikholod Ltd., Barnaul, for access to their cold room, Siberia Airline for shipping the ice, Veronica Morozova for preparing the customs documents for ice and equipment shipping and her help in expedition organization, the helicopter pilots Alexander Chebotkin and Igor Karakulko and the flight engineer Alexander Vertei for flying under the extreme "Belukha conditions", Dimitrii N. Kozlov, Sergej Derewstschikow, Vladimir Vashenzev and Andrej Jerjomin for their help during the expedition, and Henrik Rhyn for being our hot line to the world outside. REFERENCES [1] M. Schwikowski et al.,

Ann. Rep. Univ. Bern & PSI, 2000, p. 30. [2] M. Lüthi, this Annual Report. [3] A. Eichler et al., J. Glaciology 46, 507 (2000).

137

SURFACE AND BEDROCK TOPOGRAPHY OF BELUKHA GLACIER

M. LMM (VAW), M. Schwikowski (PSI), S. Olivier, H.W. Gäggeler (Univ. Bern & PSI), T. Papina (IWEP)

A glaciological survey of surface and bedrock topography conducted at Belukha glacier, Siberian Altai during a two-weeks ice coring campaign, indicated that the ice core drilling was performed at an optimal location. Englacial temperatures at 15 to 75 m below surface ranged from -16.5 to -17.3 °C.

INTRODUCTION As detailed in [1] a 140 m ice core was drilled during a two-weeks campaign on the Belukha glacier (49°48'26.3"N, 86°34'42.8"E, 4062 m asi) in July 2001. This glacier is located on a saddle between the two summits of the Belukha, the highest mountain in the Altai (4506 m asi). During the ice core drilling campaign, a glaciological survey of surface and bedrock topography was conducted. In addition, englacial ice temperatures were measured.

SURFACE TOPOGRAPHY The surface topography was measured with a Garmin handheld GPS system. Accuracies of absolute horizontal and vertical positions are 10 to 20 metres. The GPS-altitude of the borehole was 4060 metres a.s.l., in contrast to the topographical map, indicating 3090 metres altitude (Fig. 1).

ICE THICKNESS Ice thickness was measured in the main part of the glacier, with special emphasis on the western part where ice core drilling took place. A lightweight radio echo system with a centre frequency of 100 MHz was used. Individual sound­ings were performed in distances of 10 to 20 metres, yield­ing profiles of 20 to 30 traces. The data was analysed with standard seismic evaluation software. The varying signal velocity was calculated based on the density profile deter­mined from the ice core. The resulting ice thickness map is shown in Fig. 2, along with the position of the three bore­holes. The first borehole had to be abandoned at a depth of 28 m, because it reached a crevasse, the second at a depth of 85 m after application of antifreeze, since the drill got stuck, and the third reached a depth of 140 m.

ENGLACIAL TEMPERATURES Calibrated NTC thermistors were used for measurements of englacial ice temperatures in the second borehole. The ice temperature was constant at -17.25 ± 0.07°C between 15 and 75 metres depth from readings of 7 sensors (Fig. 3). It is assumed that undisturbed borehole temperatures were recorded, since temperatures did not change during the five days the thermistor cable was in the borehole. This constant temperature profile is likely to be a consequence of large lateral heat fluxes towards the high, only partially snow covered north face of Belukha.

CONCLUSIONS The drilling site was carefully chosen based on the limited knowledge available at the time of drilling. Preliminary ice thickness measurements indicated an ice thickness of more than 150 metres in the saddle centre. A suitable drilling site was found at the western margin of the glacier where ice thicknesses of 130 to 140 metres were expected. The shad­ing of the west peaks as well as the unambiguous ice flow direction were further supporting this choice. All assump­tions still hold, so that the drill location is still considered optimal.

0 ZOO 400 600 Easting (m)

Fig. 1: Surface topography map of Belukha glacier.

0 200 400 600 Easting (m)

Fig, 2 : Ice thickness map of Belukha glacier, along with the position of the three boreholes.

O r—

- 1 0 -

- 1 7 . 5 - 1 7 . 0 - 1 6 . 5 T e m p e r a t u r e ("C)

Fig. 3 : Englacial temperatures at Belukha glacier.

REFERENCES [1] S. Olivier et al., this Annual Report.

138

FIRST MERCURY DETERMINATION IN SNOW AND FIRN FROM HIGH-MOUNTAIN GLACIERS IN THE SIBERIAN ALTAI

S. Eyrikh (IWEP & PSI), M. Schwikowski, H.W. Gäggeler, L.Tobler (PSI)

A method to analyse concentrations of mercury (Hg) in snow and ice samples by Cold Vapour Inductively Coupled Plasma Mass Spectrometry ( CV-ICP-MS) has been developed. First application on samples from the Altai and the Alps indicated a low Hg concentration level.

The study of mercury concentrations in snow and ice samples from high-mountain glaciers allows assessing long-range atmospheric transport and reconstructing past and recent changes in the global biogeochemical cycle of this element. The Altai mountain region is located close to the large Hg mine in Aktach and close to major sources of air pollution in East Kazakhstan and South Siberia. Thus, this region is assumed to be influenced by regional and long-range transport of Hg.

On 10 July 2000 snow samples were collected from a 70 cm snow pit on the Aktru glacier (50°05'26"N, 87°42'08"O, 3150 m asi). On 12 July 2000 a 6 m firn core was drilled and snow samples were collected from 1.5 m deep snow pit on the Belukha west plateau (49°48'49"N, 86°32'29"E, 3895 m asi) [1]. In addition, snow samples were collected from 1.3 m snow pit at the high-alpine research station Jungfraujoch (3450 m asi, Swiss Alps). All samplings were carried out following recommendation of a protocol for ultra-clean work. All precautions have been taken to avoid mercury losses/contamination on each stage from sampling to analysis.

Mercury was analysed by Inductively Coupled Plasma Mass Spectrometry (ICP-MS ELEMENT, Finnigan MAT) equipped with a Hydrogen Generator having a membrane gas-liquid separator (Cold Vapour technique). The potential of Cold Vapour ICP-MS for Hg determination was studied with Hg standard solutions and snow samples from the Alps. Stability of Hg solutions, loss and contamination problems during storage, and the influence of acid concentration on the intensity of the Hg signal were tested [2]. The pre-cleaning procedure and type of sample container was tested. Instrumental parameters of CV-ICP-MS such as pump speed and washing time were optimised for Hg determination. The detection limit of the method, calculated as 3 times the standard deviation of the blank, is 0.4 ng L"1 (for 20 blank samples).

The results obtained by this method, using SnCl 2 as reducing agent, are operationally defined as "reactive mercury", that is Hg in ionic or weakly bonded form.

The lowest Hg concentrations were determined in the snow pit (0.8-1.4 ng L"1) and in the firn core from Belukha glacier (1.0 to 3.3 ng L"1 in dependence of depth, most values are around 1.2-1.8 ng L"1, see Figure 1 and 2). Hg concentra­tions in the snow pit from Aktru were substantially higher ranging from 3.6 to 4.4 ng L"1 (Figure 1). The highest Hg concentrations were found in fresh snow samples collected on Belukha glacier (4-4.4 ng L"1). The snow samples from the Swiss Alps (Jungfraujoch) showed a comparatively constant Hg level of 2.3-2.9 ng L"\ which is higher than that observed in snow from the Belukha glacier, but lower than in Aktru snow (Figure 1). However, it is comparable

with the concentration level recently reported for Hg in snow from the French Alps [3].

5 4.5

4 3.5 i

3 2.5 •

2 1.5 i

1 0.5

0

Belukha

Jungfraujoch

Aktru

0 100 Depth (cm)

Fig. 1: Hg concentrations in snow pits from different sites.

The concentration of Hg in the 6 m fini core from Belukha is presented in Figure 2, along with the corresponding concentration of sulphate. Both trace species show comparable concentration fluctuations, which is expected due to a joint atmospheric transport from the source areas to the remote glacier. This gives confidence in our method of Hg analysis.

80-1

70-

~ 60-

3- 50-1

~ 40-ai a

30-

20-

10-

Siiphate Hg

V •2 £.

0 1 2 3 4 5 6 Depth below snow surface (m)

Fig. 2: Concentration of Hg and sulphate in a firn core from Belukha.

The preliminary data are the first Hg concentration data for snow and ice in the Altai region. In a next step Hg concentrations in an ice core from the Belukha [4] will be studied for reconstruction of the changing contribution in the past of natural and industrial sources to the global atmospheric mercury budget, of long-range transport of Hg and of time records of Hg contamination in the Altai region.

REFERENCES [1] M. Schwikowski et al.,

Ann. Rep. Univ. Bern & PSI 2000, p. 30. [2] S. Eyrikh et al.,

Ann. Rep. Univ. Bern & PSI 2000, p.33. [3] C. Ferrari, personal communication. [4] S. Olivier et al., this Annual Report.

139

DATING OF TWO NEARBY ICE CORES FROM ILLIMANI, BOLIVIA

St. Kniisel, P. Ginot, H. W. Gäggeler (Univ. Bern & PSI), U. Schotterer (Univ. Bern), M. Schwikowski (PSI), B. Francou, J. R. Petit (LGGE-CNRS Grenoble, France), J. C. Simöes (Lav. de Pesq. Antárct. e Glac, Porto Alegre,

Brazil), J. D. Taupin (IRD-INAMHI)

The fast electrical conductivity method (ECM) was applied for establishing a chronology for two parallel ice cores from the Illimani, Bolivia. Due to the high resolution of this method, annual layers could be counted along 125 m or 90 % of the ice core, corresponding to an age at 125 m of 1200 ± 240 AD (2a error). The resulting age-depth relationship agreed well with nuclear dating using the decay of 210Pb and the 1964 tritium horizon. Furthermore acidic layers were identified and assigned to volcanic eruptions. The nitrate record of the deepest 5 m shows a remarkable resemblance with records from Sajama, Bolivia and Huascaran, Peru dated to 9-20 ky BP, indicating that the lowest meter of the Illimani core contain Wisconsin ice.

INTRODUCTION Mid and low latitude high mountain glaciers have attracted growing attention as palaeo-climate and atmosphere archives, providing for regional information e.g. in the Tropics or in Europe. An established and accurate method for dating glaciers is annual layer counting (ALC), which is even more precise when supported by identifying horizons from volcanic eruptions.

DATING Annual layers [1] could be counted over 125 m or 90 % (see figure 1), representing the time period 1200-1999 AD, limited only by significant layer thinning in the deepest part. ECM based chronologies of the two parallel cores agreed well. The resulting age-depth relationship was verified by independent methods, i.e. nuclear dating using the 1964 tritium horizon and the 2 1 0 Pb activity, resulting in a good agreement. For estimating an error of ALC, the annual layers were counted several times, resulting in the following accumulated error, e.g. 5 years (2o) at 50 m depth with a corresponding age of 72 years, 66 years at 100 m (397 years) and 175 years at 120 m (680 years).

Annual layer thickness: 1.21 ± 0.62 m f i r n 120

100

-Annual layecthtckness: 0.072 ± 0.039 m i c e

110.4 110.6

Depth [m]

Fig. 1: General appearance of the ECM and H + signal. For the detection of volcanic peaks, a first two-sigma limit was calculated separately for both firn (d < 0.82 gem"3) and ice part of the ice core. Peaks larger than the two-sigma limit were considered to be of volcanic origin. In order to average only the seasonal signal, a second two-sigma limit was calculated after removing data attributed to volcanic peaks. Known volcanic eruptions were assigned to ECM peaks using the depth in the ice cores, the approximate age (derived by ALC), the duration, the integral as well as the intensity as criteria. The very prominent peaks from the major eruptions of Pinatubo, 1991, El Chichón, 1982, Agung, 1963, Krakatau, 1883, Cosiguina, 1835, Tambora, 1815, Kuwae, 1452 and the unknown 1258 were identified

in the ECM record. Assuming that this identification is correct, the error of annual layer counting is significantly reduced to ± 2 years in the vicinity of the volcanic time markers. The obtained chronology agrees well with the age-depth relationship predicted by a firn-densification [2] and two ice-flow models [3, 4] down to a depth of about 60 m, see figure 2. In the deeper part of the core, layers thin out faster than predicted, as could be observed in other midlatitude ice cores [5]. The final age-depth relationship is obtained in the firn part by the firn densification model and in the ice part from a fit of a ice flow model [3] through age-depth points from ALC, nuclear dating and volcanic horizons.

Tambora 1815

" ^ - ^ 1 Magnification of the upper 80 m|

unknown 1258 \

—•— Firn densificatíon model (2)

Ice flow model (4)

Ice flow model (3) (UP)

Ice flow model (3) (LP)

Fitted ice flow model (3) (UP)

Fitted ice flow model (3) (LP) 1 1 '

r ^ V —•— Firn densificatíon model (2)

Ice flow model (4)

Ice flow model (3) (UP)

Ice flow model (3) (LP)

Fitted ice flow model (3) (UP)

Fitted ice flow model (3) (LP) 1 1 ' ; ™\ \

—•— Firn densificatíon model (2)

Ice flow model (4)

Ice flow model (3) (UP)

Ice flow model (3) (LP)

Fitted ice flow model (3) (UP)

Fitted ice flow model (3) (LP) 1 1 '

2000

1800

1600

1000 » <

800

600

400

200

60 80 Depth [m]

120 Bedrock: 138.7 m

Fig. 2: Age-depth relationship derived by ALC, nuclear dating, and different ice-flow models.

In the 5 m above bedrock the nitrate and the stable isotope records [6] show a remarkable resemblance with records from the Sajama and the Huascaran. The latter were dated to 9-20 ky BP, which let us assume that the lowest meters of the Illimani core contain Wisconsin ice.

REFERENCES

[ 1 ] C. U. Hammer, J. Glaciol. 25, 359 ( 1980).

[2] M. M. Herron, C. C. Langway, Jr., J. Glaciol. 25, 373 (1980).

[3] W. Dansgaard, S. J. Johnsen, J. Glaciol. 8, 215 (1969).

[4] J. F. Nye, J. Glaciol. 4, 785 (1963).

[5] L. G. Thompson et al., Science 282,1858 (1998).

[6] E. Ramirez et al., submitted to J. Geophys. Res.

140

RECONSTRUCTION OF SUBLIMATION AND PRECIPITATION FROM THE CERRO TAPADO ICE CORE (NORTH CHILEAN ANDES, 30°S)

P. Ginot (Univ. Bern & PSI), C. Kull (Univ. Bern & PAGES), U Schotterer (Univ. Bern), M. Schwikowski (PSI), H.W. Gäggeler (Univ. Bern & PSI)

Annual sublimation and total accumulation could be reconstructed from the Cerro Tapado ice core, using a new approach: The enrichment of the chemical tracer chloride due to sublimation. A pronounced increase of sublimation was observed for the deepest part of the record. The corresponding climate conditions, obtained from a glacier mass balance model, suggest a time discontinuity in the record.

In February 1998, a 36 m deep ice core was extracted from Cerro Tapado summit glacier (5536 m, 30°08'S, 69°55'W, Chile) [1] and analysed with high resolution (1.9 cm) for concentrations of major ions and stable isotopes [2]. Dating of the ice core was performed by annual layer counting, supported by the tritium 1964 horizon and 2 1 0 Pb nuclear dating. During the drilling campaign, sublimation rates of -1 .9 mm water equivalent per day (weq day"1) were meas­ured on this glacier [2]. Parallel surface snow experiments showed that the concentrations of some chemical species (Cl\ N 0 3 \ SC-42", K +) were enriched in the surface snow layer due to the effect of sublimation during the drier sea­son [3].

This enrichment effect was utilized for reconstructing an­nual sublimation rates over the complete record. For this purpose, the median concentration of chloride (61 \ig l"1) was considered to represent the concentration in freshly fallen snow. For all well-marked sublimation layers, subli­mation was quantified from the enrichment in chloride relative to the concentration in fresh snow. From the re­sulting sublimation rates and the net-accumulation, the total-accumulation could be deduced (Fig. 1). Surface melting did not contribute to the ablation, since eventually formed melt water immediately refroze a few cm below the surface. For the period 1920-1998 (0-23 m weq) a good agreement between the trends of the reconstructed total-accumulation and of precipitation in La Serena was found.

The annual total-accumulation exhibits a pronounced in­crease between 23.5 m weq depth and bedrock, which is due to an increase in sublimation. A glacier mass balance model calibrated for Cerro Tapado glacier over the hydro-logical year Feb. 1998-Feb. 1999 was used to estimate temperature and precipitation history on the basis of the reconstructed ablation and accumulation parameters. For the period 1920-1998 the model gives a mean annual sub­limation and precipitation of 240±40 mm and 540±45 mm, respectively, and a temperature of -12.4±0.2 °C. For the part between 23.5 m weq depth and bedrock, a regional cooling of -3°C and a precipitation increase of +290mm y"1

(+470 mm y"1 in winter and -180 mm y"1 in summer) resulted.

Such climatic conditions are significantly different from those recorded for the last century. Therefore, we assume that Cerro Tapado glacier is composed of a relict ice layer frozen to bedrock, which is covered by an active glacier part flowing above, dated to 1999-1920 (Fig. 2).

1600

0 5 10 15 20 25 Depth (m weq)

Fig. 1: Mass balance terms reconstructed from the Cerro Tapado ice core.

!ce Core 36 m

4Í111IIP pi i illl lili

II I I I 1 ' i I

i Fig. 2: Schematic of Cerro Tapado glacier, showing the

relict ice body separated from the active part.

REFERENCES:

[1] P. Ginot et al., Ann. Rep. Univ. Bern & PSI 1999, p. 37. [2] P. Ginot, Ph.D. Thesis, Univ. Bern (2001). [3] P.Ginot et al., J. Geophys. Res. 106, 32,375 (2001).

141

PERTURBATION OF THE CHIMBORAZO GLACIO-CHEMICAL RECORD BY VOLCANIC ERUPTION AND MELT WATER PERCOLATION

M. Schwikowski, M. Godoi, S. Britisch, L. Tobler (PSI), P. Ginot, H.W. Gäggeler (Univ. Bern & PSI), U. Schotterer (Univ. Bern), B. Francou (IRD, Quito)

An ash layer deposited on the Chimborazo summit glacier from the eruption of two nearby volcanoes caused a significant perturbation through melt water percolation of the concentration records of ionic species. This indicates how vulnerable such unique archives are, and how urgent the task is to recover palaeo environmental information from those glaciers shrinking rapidly due to climatic warming.

Several firn and ice cores were retrieved from the summit of Chimborazo (1°30'S, 78°50'W), Ecuador, by two joint French-Swiss-Ecuadorian expeditions in Dec. 1999 and Nov.-Dec. 2000. In Oct., Nov. and Dec. 1999 and April 2000, two of Ecuador's active volcanoes, Guagua Pichincha (0°10'S, 78°36'W) and Tungurahua (1°30'S, 78°26'W) erupted several times [1]. This covered the smooth glacier surface observed in 1999 with a thick ash layer, causing massive melting and transformation into a vast field of penitents up to 1 m high in November 2000; see [2]. Between the penitents, melt water was present. However, no significant ice layers were seen in the top most 15-m firn part of the core, suggesting that the melt water percolated through to the firn/ice transition. The effect of the volcanic ash layer and the melt water percolation on the glacio-chemical stratigraphy could be studied by comparing the 1999 and 2000 records.

The two shallow firn cores of 15 and 17 m length recovered from the Ventimilla summit (6230 m) in 1999 and 2000, respectively, were sub-sampled with 5 to 8 cm resolution, and concentrations of major ionic species were analysed by ion chromatography and the stable isotope ratios 5 1 8 0 and 5 2H by isotope ratio mass spectrometry. The 1999 and 2000 records were adjusted, using the characteristics of the ammonium records. The best fit was obtained with a lag of 0.26 m weq, which is in accordance with the shift in the 5 1 8 0 record. The stable isotope records from the two years agree well, except for the 1 m surface layer. This part was altered completely by ash layer induced melting. The effect of melting on glacio-chemical records was different for the different chemical tracers. Whereas the ammonium record with its seasonal variation was almost preserved, a strong perturbation of e.g. the sulphate and calcium in the 2000 record was observed (Fig. 1). The seasonal signal disap­peared totally in the upper 3.5 m weq of the 2000 record, resulting in a nearly flat signal. At 4 m weq depth a huge sulphate peak is present in the 2000 record, which is absent in the 1999 record. This suggests that sulphate was relo­cated by melt water percolation and was fixed at 4 m weq. The ions least influenced by melt water percolation are ammonium and nitrate. A comparable effect of melt water percolation was observed in an Alpine ice core [3]. There, chloride was the best-preserved ion, followed by fluoride, ammonium, and nitrate, which was mainly explained by their different solubilities in ice. However, in the Chim­borazo 2000 core, relocation of ionic species by melt water percolation was not the only effect perturbing the record. This becomes obvious when the total fluxes of ions are compared for 1999 and 2000 (Tab. 1). Only for nitrate and calcium the fluxes of the two records agree, whereas for fluoride, chloride, sulphate, and magnesium a significantly

higher flux was observed in the 2000 core. This indicates additional input of these ions, leached from the volcanic ash layer deposited before the core was retrieved. Such input is expected for the acidic components, but is astonishing for magnesium. Formiate, sodium, ammonium, and potassium show a higher flux in 1999, indicating partial relocation by melt water percolation, probably down to the firn/ice tran­sition, which is not covered by the record.

C o n e , (ppb) 0 200 400 0 1000 2000 3000

0-

0

CL

Fig. 1: Concentrations profiles of ammonium (left) and sulphate (right) from the 1999 and 2000 cores (0 m weq corresponds to the surface in 2000).

Table 1: Total flux in ueq cm-2 of various ionic species for the 9 m weq overlapping records from 1999 and 2000.

1- CI SO. N 0 3 Ca I o N,I M l . K 99 0.2" 1 . - - O.-y 1.95 4.05 I 00 0.6o 2.64 L.40 1.90 4.25 2 (>s 0 f>3 4„52

REFERENCES [ 1 ] http://www.ngdc.noaa.gov/seg/hazard/vol_srch.html [2] P. Ginot, Ph.D. Thesis, Univ. Bern (2001). [3] A. Eichler et al., J. Glaciology 46, 507 (2000).

142

SEARCH OF A SUITABLE GLACIER ARCHIVE IN THE BERNINA AREA

Th. Jenk (Univ. Bern & PSI), M. Schwikowski, M. Saurer (PSI), M. Lüthi (VAW), H.W. Gäggeler (Univ. Bern & PSI)

Shallow firn cores from the Piz Zupo saddle were analysed to investigate the potential of this glacier as palaeoclimate archive. Glacio-chemical records are preserved and not destroyed by melting, but the records are too short for a final dating and estimation of annual accumulation.

Within the NFS NCCR climate project VITA (Varves, ice cores and tree rings - archives with annual resolution) one of the major questions is if we already experience a human induced increase in climate variability (http://www.nccr-climate.unibe.ch/Research/projects/Pl.3.html). To address this question climate variability has to be investigated over a time period extending that one documented by instrumental data. The approach taking within VITA is to explore a combination of different natural archives that are able to record environmental and climatic changes on the highest possible time scale: lake sediments, alpine ice cores, and tree rings. Aim of this study was the search of a suitable glacier archive in the Bernina area, where the other archives can be found in close vicinity (Upper Engadin).

The most potential glacier archive in the Bernina area is the glacier saddle between Piz Zupo and Piz Argient [1]. In order to investigate preservation of glacio-chemical records and accumulation rates, shallow firn cores were drilled in the saddle (3870 m asi, 46°22'1"N, 9°55'42"E) and on a knoll just below (3840 m asi, 46°22'13"N, 9°55'24"E) on 19 May 2001. Radio-echo soundings conducted at both sites showed a glacier thickness of 40-50 m at the saddle and about 30 m at the knoll. Firn cores were sub-sampled with 5 cm resolution, and concentrations of major ionic species were analysed by ion chromatography and the stable isotope ratios ô 1 8 0 and ô 2H by isotope ratio mass spectrometry. Records of ionic species seem well pre­served, especially in the core from the saddle, indicating that melt water percolation was negligible. Therefore and because of larger glacier thickness, only results from the saddle are discussed here. Dating of the core was attempted by annual layer counting of the seasonally varying parameters ô 1 8 0 and concentration of ammonium, illus­trated in Fig. 1. The two parameters give totally different results: 12±1 years from ô 1 8 0 and 3±1 years from ammo­nium layer counting for the 3 m water equivalent (m w. eq.) core, respectively, with a corresponding annual accumula­tion of 0.25 and 1 m w. eq. However, the mean ô 1 8 0 value

of -13.0 %o is significantly higher than presumed from the empiric linear relationship between ô 1 8 0 in precipitation and elevation of the sampling site. This was already ob­served for two other glacier sites, at the Colle Gnifetti and at the Jungfraujoch plateau, and was explained by wind erosion of winter snow [2]. We assume that wind erosion could also take place at the Piz Zupo saddle, leading to a low net accumulation and favouring the dating by ô 1 8 0 . The prominent Sanaran dust horizon observed at 2.7-2.9 m w. eq. in the core from the saddle (Fig. 1) offers another dating tool. It could originate from the major Sanaran dust trans­port event observed on 20-23 March 1990 at the Jungfrau­joch [3], which was also seen in an ice core from the Gren-zgletscher [4]. However, the total calcium flux - used as dust indicator - at the Piz Zupo saddle was an order of magnitude higher (1.7 g m"2) than at the two other sites. This could indicate that the dust horizon in the Piz Zupo core originated from another Sanaran event, possibly from the one observed in the Tessin, e.g. on the Basadino glacier, on 13-15 October 2000 (G. Kappenberger, SMA, personal communication). In this case, the core would only cover about 8 month, resulting in an extremely high annual accu­mulation rate of more than 3 m w. eq. Thus, the available data do not allow a final dating or estimation of the accu­mulation rate.

ACKNOWLEDGEMENTS

This work was supported by the Swiss National Science Foundation within the NCCR climate project VITA.

REFERENCES [1] H.W. Gäggeler et al., in Symp. Radioaktivitätsmessung in

der Schweiz nach Tschernobyl und ihre wiss. Interpretation, Band 1, 238-248 (1986).

[2] W. Stichler et al., Hydr. Processes 14, 1423 (2000). [3] M. Schwikowski et al., Atmos. Environ. 29, 1829 (1995). [4] A. Eichler, J. Glaciology 46, 507 (2000).

2001 1 9 9 9 1 9 9 7 1 9 9 5 1 9 9 3 1991 2 0 0 0 1998 1996 1994 | 1 9 9 2 1990

- 1 0 --1 2

O -14 °° - 1 6 -

(O -18 -20 -2 2

50 1 0 0* 150 200 2001 2 0 0 0 1 9 9 9

CT 4

I 20 -c 15 -o 1 0 -

J o - 1

2 5 0 1 998

300

1 50 2 0 0

D e pth [cm w . e q .] Fig.1: ô l s Oand ammonium record with attributions of annual layers. The prominent dust horizon is indicated (grey bars).

143

FIRST SHALLOW FIRN CORE RECORDS FROM GORRA BLANCA, PATAGONIA M. Schwikowski, S. Brütsch, M. Saurer (PSI), G. Casassa (CECS, UM AG), A. Rivera (UCh, CECS)

Glacio-chemical records from Gorra Blanca indicate considerable influence of melt water percolation up to an elevation of 1800 m. At 2300 m, the investigated topmost 5 m fini showed no significant signs of melting. Thus, the higher elevation glaciers of the Southern Patagonia Icefield might be suitable as paleoclimate ice archives.

The Southern Patagonia Icefield (SPI) is the largest body of ice in the Southern Hemisphere outside of Antarctica. It is located along 73°30' W between 48 and 51° S with an area of about 13'000 km 2 and an elevation from 800 to 2000 m, with a few peaks exceeding 3000 m. The climate in the mid-latitudes of southern South America is dominated by the westerly circulation regime. The southern westerlies are considered as a key component of the global climate sys­tem, since they may have an impact on the amount of car­bon dissolved in the Southern Ocean, on the extent of Ant­arctic sea ice, and on global thermohaline circulation [1 ,2] . Ice core records from SPI would provide an opportunity to investigate changes in the position and strength of the west­erly airflow trough time. Despite of this fact only a limited number of investigations have been carried out there [3, 4]. This is due to the extremely difficult fieldwork in this re­gion, where strong winds and precipitation prevail most of the times. In addition, melting caused by relatively warm temperatures largely influences the glaciochemical records. In order to explore the suitability of different glacier sites at the SPI as paleoclimate archives, three shallow firn cores were drilled during the fourth expedition of the Icefields Science Initiative, organised by CECS. The main aim of this study was to search for higher elevation glacier sites, which are assumed to be less influenced by melt water formation and percolation. A 4-m and a 3-m core were retrieved on 25.9. and 27.9.2001 from Paso Marconi (49° i r2 .1" S, 73°08 ,40.3" W, 1543 m asi) and from Gorra Blanca Sur (49°0922.6" S, 73°06'51.9" W, 1836 m asi). The drilling sites were approached from the Marconi base camp by snowmobile. Drilling had to be stopped at 4 and 3 m depth, respectively, because ice or a thick ice lens was encountered. On 28.09.2001 a 5-m core was collected from the Plateau of Gorra Blanca Norte (49°07'52" S, 73°03'11" W, 2300 m asi), which was reached by helicopter. On the same day, a reconnaissance flight was carried out over Cerro Pirámide and Cordón Gaea, showing that both sites are too steep for drilling. The firn cores were packed and sealed in polyethylene bags in the field, shipped frozen to PSI, and kept frozen in a cold room (-25°C) until analysis. The cores were sub-sampled with 5 cm resolution, and concentrations of major ionic species were analysed by ion chromatography and the stable isotope ratios ô 1 8 0 and ô 2H by isotope ratio mass spectrometry. Records of sodium concentrations and of ô 1 8 0 for the cores from Gorra Blanca Sur (GBS) and from the Plateau of Gorra Blanca Norte (GBP) are compared in Fig. 1 and 2. At GBS fluctuations of both parameters are observed to a depth of about 100 cm water equivalent (weq). Deeper down a constant level is reached, indicating that the 2001 winter precipitation signal is still preserved in the record, whereas the signal further down was destroyed by percola­tion of melt water. This is consistent with the thick ice layers encountered already at 3 m below the surface. An accumulation in winter of about 0.5 to 0.8 m of water (Fig.

2) would be in reasonable agreement with the annual accu­mulation of 0.9 to 0.2 m water measured from 1996 to 2000 at Marconi base camp [5]. At GBP, on the other hand, variations in all parameters are observed in the 5-m core (250 cm weq), indicating that no significant melting oc­curred. This is supported by the visual stratigraphy, where only thin ice layers of less than 1 cm were seen. Either the accumulation on GBP is much higher and the last summer layer, possibly influenced by melting, was not reached, or, more probably, the site is located high enough and is not significantly influenced by melting, in which case the ac­cumulation according to Fig. 2 would be about 1 m water.

GBP2300mas l

Depth (cm weq)

Fig. 1: Sodium concentrations in the cores from Gorra Blanca Sur (GBS) and from the Plateau of Gorra Blanca Norte (GBP).

GBP 2300 m as i S P S îîi iíiíí

0 50 100 150 200 250 300

Depth (cm weq)

Fig. 2: ô 1 8 0 records from GBP and GPS. ACKNOWLEDGEMENTS We thank the Fuerza Aérea de Chile (FACH) for the logis­tic support, Abraham Bastías (FACH), Fernando Adasme (FACH), Soeren Wedel Nielsen, Gabriel Cabrera and for the help in drilling, Francisco Sepulveda (expedition leader, CECS) and CECS for organising and funding the expedi­tion through the Millennium Science Initiative. REFERENCES [1] J. Imbrie et al., Paleoceanography 7, 701 (1992).

J.R. Toggweiler et al., Deep See Res. 1,477 (1995). A.J. Aristarain et al., J. Glaciology 4, 132 (1993). M.A. Godoi et al., in: The Patagonian Icefields, to be published by Kluwer Academic. G. Casassa, A. Rivera,. Int. Symp. on the Verification of Cryospheric Models, August 16-20,1999, Zürich, p. 44.

[2] [3] [4]

[5]

144

MELT WATER AND NITRATE RELEASE FROM A MELTING SNOW PACK

P. Waldner, M. Schneebeli (WSUSLF), M. Schwikowski (PSI)

An enormous heterogeneity of the melt water flow was observed in a subalpine snow cover in winter 1998/1999. It is explained by lateral and vertical preferential flow paths in the snow cover. The variability of the nitrate concentration in the melt water is to a large extent due to the nitrate concentration in the contributing snow layers.

1 INTRODUCTION

Chemical trace species in precipitation are a relevant source of rare nutrients for the vegetation. These nutrients are stored in the snow cover during winter and are released during snow melt, resulting in significant nutrient input into soil, vegetation and rivers. The effect of the nutrients on plants, soil and rivers depends on the temporal and spatial distribution of the release. The nutrient considered in this study is the nitrogen containing the ionic species nitrate. The relations between melt water and nutrient release of a snow cover and the influence of the structure of the snow cover and of meteorological conditions on these processes were jointly investigated by WSL/SLF, ETHZ and PSI in the frame of the NF-project "Nutrient release of melting snow".

2 M E T H O D S

In winter 1998/1999 a field campaign was conducted in order to measure the spatial and temporal variations of the melt water release of a subalpine snow cover. For this purpose a network of 32 melt water samplers was installed on a not-forested field in Alptal (1210 m a.s.l.). The Alptal area has a long tradition of field experiments concerning catchment hydrology and nutrient budgets [1, 2]. Melt water was periodically collected from the samplers and snow pit sampling was performed. Samples were analysed for concentrations of nitrate by ion chromatography. At about 20 cm above soil surface, liquid water content was continuously monitored with time domain reflectometry probes (TDR) [3].

3 RESULTS AND DISCUSSION

Extraordinary amounts of snow in the winter 1998/1999 resulted in a highly layered and structured snow pack (Fig. 1). In the snow pit, wet layers indicated a capillary barrier effect of layer boundaries on the percolating melt water. Three types of water fluxes were identified: (i) A base melt flow induced by the heat flux of the marshy soil, (ii) a surface melt water percolation, and (iii) a highly saturated lateral flow in the bottom layer of the snow pack. The surface melt percolation showed an enormous variability that is explained by horizontal and vertical preferential flow paths. The formation of these paths was driven by hori­zontal heterogeneity and hydraulic instabilities at the capil­lary barriers (Fig. 1). Melt water exceeding infiltration capacity accumulated in the bottom snow layer and was laterally flowing down-hill. This saturated flow reached the level of the TDR probes, where liquid water contents rose up to 0.45 m 3 m"3.

In comparison, the variation of the nitrate concentration in the melt water is to a large extent explained by the nitrate concentration of the snow layer where the melt water

originated from. The nitrate release calculated from the change of the nitrate stored in the snow cover and the input by precipitation agrees well with the measured release (Fig. 2). The redistribution of ions at the snow grain scale during snow metamorphism had only a minor effect on the nitrate release as the nitrate concentrations were near its solubility in ice [4] and temperature gradients within the snow pack were small.

0 1 2 3 1 2 3 4 wetness number

grain size [mm]

Fig. 1: Translucent, density and wetness profile from the snow pit of March 30, 1999.

3

2

£ 1

go o>

J= -1

-•—snow cover -X—precipitation (cum.) -O— release meas, (cum.) + release calc. (cum

-2

-3

Nov Dec Jan Feb Mar Apr

Fig. 2: Nitrate balance of the snow cover in 1998/1999. REFERENCES [1] H. Burch, Beiträge zur Hydrologie der Schweiz 35,

18 (1994). [2] P. Schleppi et al.,

Water, Air and Soil Pollution 116,129 (1999). [3] M. Schneebeli, C. Coléou, F. Touvier, B. Lesaffre,

Ann. Glac. 26, 69 (1998). [4] A. Eichler, M. Schwikowski, H. W. Gäggeler,

Tellus Series B 53, 192 (2000).

145

THEODORE: A NEW SAMPLE PREPARATION SYSTEM FOR THE 1 4 C DETERMINATION IN THE OC AND EC FRACTION OF AEROSOLS

S. Szidat (Univ. Bern), H.W. Gäggeler (Univ. Bern & PSI), H-A. Synal, M. Saurer (PSI), I. Hajdas, G. Bonani (ETHZ)

14C/2C values of carbonaceous aerosol particles give a unique and absolute measure of the contemporary to fossil carbon source ratio, which can be used for source apportionment of biogenic and anthropogenic emissions. Here, we present the experimental set-up of the used THEODORE system as well as first results of sample preparation methods and accelerator mass spectrometry (AMS) measurements for the14 C determination in OC and EC.

Investigations on carbonaceous airborne particles are of increasing interest with respect to climatic, environmental and health effects of aerosols. Various organic substances represent a significant fraction especially of the fine particle mode. Due to their special thermal and chemical behaviour, a differentiation is made between simple organic compounds up to light polycyclic hydrocarbons (organic carbon, OC) and highly polymerized, graphitic matter (elemental carbon, EC), which is also designated as black carbon (BC) referring to its optically absorptive character. The fraction of modern (fM) expresses a ratio of an actual 1 4 C/ 1 2 C to that of the reference date 1950 [1]. As 1 4 C has become extinct in fossil fuel, one can determine the fossil fuel contribution directly from a measured fM.

The challenging aspect is that the expected amounts of EC and OC available from aerosol samples are only in the ¡xg-range. This is very low compared to carbon masses used for routine 1 4 C determinations. Thus, a major improvement in sample preparation was necessary, which was achieved by developing the new system THEODORE (set-up is sketched below). For the separation of EC and OC from PM2.5 on pre-heated quartz-fibre filters, a previously developed method was chosen [2], which has proven to be suitable for the determination of total EC and OC in a round robin test of urban aerosols [3]. This method was adjusted to the demands of 1 4 C analysis: OC and EC are combusted in an oxygen atmosphere at 340 °C and 650 °C, respectively. A rapid heating procedure from room temperature to the first thermal stage within half a minute reduces charring artefacts which means in-situ formation of additional EC from OC; this would increase 1 4 C/ 1 2 C ratios of EC, which normally has a minor fM than OC. Both C 0 2

fractions are trapped cryogenically, separated from interfering reaction gases, quantified manometrically in a calibrated volume, and sealed in quartz tubes for the next step.

\A&ter reservoir (decontamination)

For the preparation of the AMS target material from carbon dioxide, the reduction with manganese in the presence of cobalt at 540 °C was chosen. It was invented especially for samples like aerosols containing a carbon mass down to a few microgram and can be carried out in a sealed ampoule, which allows a very small reactor volume [1]. The routine graphitzation method at PSI/ETH, the reaction on a cobalt catalyst at 620 °C, proved to be inappropriate for our pur­pose, because measured 1 4 C/ 1 2 C ratios showed an unsatis­factory reproducibility.

1 4 C measurements are performed at the PSI/ETH compact AMS system, based on a 500 keV pelletron accelerator [4]. Samples containing 50 ¡j,g carbon achieved a 1 2 C ion current on the low-energy end of the accelerator of 5.2 ± 1.5 uA at the 1 + charge state which corresponds to about 30 % of the current of routinely measured milligram samples. Under those conditions 1 4 C/ 1 2 C ratios in samples w i t h / M of 0.5 could be determined with an uncertainty of 3% (1 a) .

ACKNOWLEDGEMENT This work contributes to the EUROTRAC-2 subproject AEROSOL and is supported by the Swiss National Science Foundation.

REFERENCES

[1] R. M. Verkouteren et al., Radiocarbon 39, 269 (1997).

[2] V. M. H. Lavanchy et al.,

Atmos. Environ. 33, 2759 (1999).

[3] H. Schmidt et al., Atmos. Environ. 35, 2111 (2001).

[4] H.-A. Synal et al., Nucl. Instrum. Meth. B 172, 1 (2000).

850-C

Calibrated Tibes for volume for CGv off-line determination graphitization

Fig. 1: Two-step heating combustion system for the EC/OC separated determination of radiocarbon in the environment (THEODORE)

146

ATMOSPHERIC 7 Be AND 2 1 0 P b ACTIVITY CONCENTRATIONS AT THE HIGH-ALPINE SITE JUNGFRAUJOCH

L. Tobler, M. Schwikowski (PSI), H.W. Gäggeler (Univ. Bern & PSI)

Atmospheric activity concentrations of the radionuclides 7Be and 210Pb have been measured at the Jungfraujoch (3580 m a.s.l) within the EU project STACCATO (Influence of Stratosphere-Troposphere Exchange in a Changing Climate on Atmospheric Transport and Oxidation Capacity). Data of the time period January 2000 to October 2001 are analysed and compared to previous time periods.

The use of naturally occurring radionuclides as tracers for investigating atmospheric processes in the atmosphere is well established. 7 Be is formed through spallation reactions of light air constituents by cosmic ray particles. 7 Be production takes place mainly in the stratosphere (about 66 %), while the rest is produced in the troposphere. 2 1 0 Pb is produced by the decay of the actinide 2 3 8 U , which is mainly contained in the lithosphère. In the decay chain of 2 3 8 U , one intermediate decay product is 2 2 2 Rn, an isotope of the noble gas radon. This gas emanates from the lithosphère into the atmosphere and decays to the long-lived 2 1 0 Pb. After formation, 7 Be and 2 1 0 Pb atoms become attached to ambient aerosol particles. Since the attachment is irreversible, the fate of the 7 Be and 2 1 0 Pb atoms is determined by the mechanisms governing the transport and removal of aerosols.

On a routine basis, aerosol particles are collected on glass fibre filters at the high-alpine research station Jungfraujoch with a time resolution of 48 h by the NABEL network [1]. Over the past 22 months measurements of 7 Be and 2 1 0 Pb have been performed on these filters in the framework of the EU project STACCATO. 7 Be (T 1 / 2 = 53.12 d) and 2 1 0 Pb (Ti/2 = 22.3 y) activities are measured on one half of the filters by high-resolution y-spectrometry in a well-type Ge-detector. All activity results are corrected for decay during sampling and measurement. All activities per air volume are corrected to standard pressure and temperature. Counting error is on average 4 % for 7 Be and 30% for 2 1 0 Pb. The quality of the 7 Be data has been proved by an intercomparison exercise of different laboratories [2].

Basic statistics of activity concentrations of 7 Be and 2 1 0 Pb are given in Table 1. 2 1 Pb activity was detected only in 69% of all filter samples. In order to calculate mean values, it was assumed that samples below the detection limit (DL) of 0.23 mBq/m 3 have an activity concentration of one half of this.

Table 1: Basic statistics of 7 Be and 2 1 0 Pb activity cone.

7 Be [mBq/m3] 2 1 0 Pb [mBq/m3] Year 2000 2001 2000 2001 Median 5.49 5.38 0.36 0.32 Min 0.43 0.55 <0.23 <0.23 Max 14.7 17.7 1.12 1.30 No Obs. 182 151 182 151 Obs >DL 182 151 125 103

Frequency distribution analysis of 7 Be (Fig. 1) shows a similar distribution to the one observed by Geraspoulos et al. [3] for the time period 1996-1998 at the same location. However, the median of all values (7 mBq/m3) was higher in this former time period.

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 7 B e [mBq/m3]

Fig. 1: Frequency distribution of 7 Be activity concentrations January 2000 - October 2001 (n=332).

Monthly arithmetic means of 2 1 0 Pb activity concentrations are shown in Fig. 2. They exhibit a small seasonal trend with a maximum in August, consistent with monthly 2 1 0 Pb values measured by oc-spectroscopy at the Jungfraujoch during 1991 [4]. The higher values of the y-measurements might be explained to a large extend by the method of the consideration of the detection limit values.

10 11 12

Fig. 2: Monthly mean values of Pb activity concentration

ACKNOWLEDGMENT

This study is part of the EU research project STACCATO (Contract No. EVK2-CT1999-00050) and is funded by the Bundesamt für Bildung und Wissenschaft (BBW) of Switzerland. The sampling and the delivery of the filters by the EMPA (operator of the NABEL network of BUWAL) are highly appreciated.

REFERENCES [1] NABEL Luftbelastung 1999, BUWAL SRU316 (2000). [2] L. Tositti et al., Atmospheric Environment, submitted. [3] E. Gerasopoulos et al., Atmos. Environ. 35, 6347

(2001). [4] H.W. Gäggeler et al., Atmos. Environ. 29, 607 (1995).

147

1 0 Be/ 7 Be RATIOS AT THE HIGH-ALPINE SITE JUNGFRAUJOCH TO STUDY STRATOSPHERE -TROPOSPHERE EXCHANGE

C. Schnabel (Univ. Bern & ETHZ), P.W. Kubik, L. Tobler, M. Schwikowski (PSI), H.W. Gäggeler (Univ. Bern & PSI)

The particle bound atmospheric concentrations of the cosmogenic radionuclides 7Be and 10Be have been measured at the Jungfraujoch (3580 m a.s.l.) within the EU project STACCATO (Influence of Stratosphere-Troposphere Exchange in a Changing Climate on Atmospheric Transport and Oxidation Capacity). The ratio 10Be / 7Be is used as a probe for the intrusion of stratospheric air masses into the troposphere.

Stratospheric intrusions lead to increases of ozone and Be concentrations in the troposphere as well as to a decrease in relative humidity. But those effects on ozone, 7 Be and relative humidity can also occur if dry air masses descend from the upper troposphere. Moreover, 7 Be concentrations can also be affected by scavenging processes.

Thus, it was proposed [1] to use the isotopic ratio 1 0 Be/ 7 Be as a probe for atmospheric transport processes. Raisbeck et al. [1] and Dibb et al. [2] found l ö Be/ 7 Be ratios ranging from 4.0 to 6.9 in the lower Arctic stratosphere during two sampling periods. Consequently, an average of 5.2±1.0 may be used as a best guess for the 1 0 Be/ 7 Be ratio for Arctic air masses of the lower stratosphere. Because most of the stratospheric intrusions to the Alps originate form higher latitudes, this ratio may nevertheless be used as the 1 0 Be/ 7 Be ratio of a stratospheric tracer that has entered the troposphere and is investigated at the Jungfraujoch. Dibb et al. [2] used a tropospheric residence time of 30-40 days for 7 Be, a mean observed 1 0 Be/ 7 Be ratio in the troposphere and an estimated production rate ratio of the isotopes 1 0 Be and 7 Be to estimate the average stratospheric contribution to the polar troposphere. In our preliminary approach we use just the 1 0 Be/ 7 Be ratios observed before the intrusion as the isotopic ratio of the pure troposphere before mixing and a 1 0 Be/ 7 Be ratio of 5.2 for the stratospheric contribution to estimate the relative amount of stratospheric air that was sampled.

In April 2001, several stratospheric intrusions were observed at the Jungfraujoch. Fig.1 shows the ozone concentration and the relative humidity as 24 hour averages as well as the particle bound 1 0 Be/ 7 Be ratios measured on air filters sampled at the Jungfraujoch using a HIVOL air sampler. The pronounced maximum in ozone concentration together with a minimum in relative humidity on April 12-14 indicates a stratospheric intrusion. The drop in relative humidity is not very strong due to the fact that the air masses cooled down in this case. Particulate 1 0 Be/ 7 Be ratios increased from 1.02 before the intrusion to 2.62 on average for the period from April 11 to April 15. From this we estimate preliminarily a content of about 40% stratospheric air sampled on average during these four days. For the next stratospheric intrusion on April 21-22, using the data point from April 15 to April 20 as baseline, one can estimate a

contribution of about 60% of stratospheric air from this new intrusion for the 48 h sampling period. The maximum in 1 0 Be/ 7 Be ratio on April 25 - 26 also reflects a stratospheric input, which is supported by ozone and humidity data.

30.3.01 04.4.01 09.4.01 14.4.01 19.4.01 24.4.01 Date

Fig. 1: Ozone concentration, relative humidity and 1 0 Be/ 7 Be ratios at the Jungfraujoch in April 2001.

ACKNOWLEDGMENTS

This study is part of the EU research project STACCATO (Contract No. EVK2-CT1999-00050) and is funded by the Bundesamt für Bildung und Wissenschaft (BBW) of Switzerland. The sampling of the filters by the EMPA (operator of the NABEL network of BUWAL) and especially their delivery by Robert Gehrig (EMPA) are highly appreciated. We acknowledge the delivery of relative humidity data by Meteo Schweiz, Kundendienst Bodendaten, Zürich. We thank the Swiss Agency for the Environment , Forests and Landscape BUWAL for the ozone data. Technical assistance by I. Gomez Martinez and G. Leone is greatly appreciated.

REFERENCES

[1] G. M. Raisbeck et al., Geophys. Res. Lett. 8, 1015 (1981).

[2] J. E. Dibb et al., J. Geophys. Res. 99, 12855 (1994).

148

APPLICATION OF NEUTRON ACTIVATION ANALYSIS AT SINQ

L. Tobler, M. Schwikowski (PSI)

Neutron activation analysis (NAA) has been challenged by many other analytical techniques in the last decade. However, NAA can still play an important role as analytical tool in many cases. This will be shown by an application of NAA in solid-state physics, the determination of zinc in Zn-doped GaN crystals.

INTRODUCTION

Very sensitive and accurate analytical techniques, i.e. ICP-MS and ICP-OES, have diminished the importance of neutron activation analysis (NAA) as an analytical tool for trace element determinations [1]. Very often analytical techniques are compared in a competitive fashion, but they have to be applied in a complementary way. Neutron activation analysis still has its merits in analytical chemistry, especially for the analysis of solid samples. The neutrons penetrate the whole material and allow bulk analysis of the samples. An application of NAA for a problem in solid-state physics is presented, which will show that analytical techniques must be chosen to match samples, rather than vice versa.

DETERMINATION O F ZINC IN ZN-DOPED GaN-CRYSTALS

Semi-conducting nitrides of the group III elements (Al, Ga, In) have become commercially available, high efficiency solid-state devices. An advantage of the nitrides over other high-bandgap semiconductors is the strong chemical bond, which makes the material very stable and resistant to degradation under conditions of high electric currents and intense light illumination. However, this stability makes it impossible to dissolve the samples, which is a prerequisite for many analytical methods.

GaN crystals have been doped with zinc, but the total amount of Zn was unknown until now. Different methods have been tried for the determination of zinc in these crystals without success. Neutron activation has been found to be adequate to quantify the Zn concentrations in this material.

The determination of Zn by NAA involves two main reactions: (I) 6 8 Zn (n,y) 6 9 m Z n half-life: 13.8 h (II) M Z n (n,y) 6 5 Zn half-life: 244.3 d

The first reaction is not suited for the determination of Zn in GaN, due to the fact, that the matrix element Ga induces a high activity of 7 2Ga, which decays with a similar half-life (14.1 h) as 6 9 m Zn. This activity hampers the detection of 6 9 m Zn. The determination of Zn by the second reaction is possible after an appropriate decay time. However, due to the presence of high-energy neutrons at the irradiation position of the neutron source SINQ [2, 3], the interfering reaction 6 9 ' 7 1 Ga (n,xn) 6 5 Ga occurs and has to be taken into account. The short lived isotope 6 5 Ga decays with a half-life of 15 minutes into 6 5 Zn and pretends an apparent Zn content. By the irradiation of non-doped (Zn free) GaN crystals, it is possible to correct for this interfering reaction.

Two GaN crystals of each type (non-doped and Zn-doped; weight 5 mg) were packed into polyethylene vials and transported together with Zn- and Ga- standards (100 \ig each) to the neutron source SINQ by a pneumatic transfer system [4]. Irradiation time was 40 minutes at a thermal neutron flux of 4.5 10 1 2 n/(cm2s). The irradiated samples were measured on a high-purity Ge detector to detect the characteristic y-lines of 7 2 Ga (630 keV, 834 keV) and 6 5 Zn (1115 keV). The detector was connected to an Open VMS-based data acquisition and analyses system (Genie, Canberra Industries, Inc.). The following measurement schedule was applied:

Determination Decay Measurement time time

Ga 6 d 2 h Zn 16 d 12h

Ga concentrations found were 81% and 88.7% for doped and non-doped crystals respectively (true stoichiometry of GaN 83.27%). Non-doped GaN showed an apparent Zn content of 297 Hg/g Ga, for which the Zn concentrations of the doped GaN crystals had to be corrected:

CZn (true) = CZn (meas.) - 297 • C G a , with Cx : concentration of element x.

Zn concentrations of the two doped crystals were 721 ppm and 869 ppm after this correction. Counting error was < 1% for Ga, 6% respectively 20% for Zn in doped and non-doped crystals.

ACKNOWLEDGEMENTS

Special thanks are due to H.U. Aebersold for managing and maintaining the pneumatic transfer system. Our thanks are extended to the staff of the SINQ and the radiation safety group.

REFERENCES

[1] V. P. Guinn, J. Radioanal. Nucl. Chem. 244/1, 23 (2000).

[2] G. S. Bauer, PSI Report, The Spallation Neutron Source SINQ (1994).

[3] E. J. Szondi et al., in Reactor Dosimetry, ASTM STP 1398, eds. J. G. Williams et al, American Society for Testing and Materials, West Conshohocken, 401 (2001).

[4] L. Tobler et al., Extended Abstracts, 5 t h Int. Conf. on Nuclear and Radiochemistry, Vol. 1, 362 (2000).

149

TRACE ELEMENT ANALYSIS OF SOME LOW AND MEDIUM Z ELEMENTS IN ICE SAMPLES BY TOTAL REFLECTION X-RAY FLUORESCENCE (TXRF)

N. L. Misra (BARC, India), L. Tobler, M. Schwikowski (PSI)

A TXRF method for was develped for analysis of low and medium Z elements in ice samples. Multielement standards as well as ice samples were analyzed for elements Si, P, S, K (19) to Se (34) and Rb (37) - Mo (42) using Kalines and U, Th and Pb using La lines. An intercomparision with ICP-MS was also made.

In recent years TXRF has been increasingly used for the trace element analysis in various research areas due to its inherent capabilities [1]. It may be suitable for ice samples also, particularly when these contain insoluble particles and for low Z elements. Our earlier attempts of trace element analysis of ice samples by TXRF showed a comparatively large deviation from ICP-MS analysis results [2]. Studies were made to remove the discrepancies by improved pre-concentration of the samples and optimization of instru­mental parameters for low and medium Z elements sepa­rately. The TXRF spectrometer developed at Paul Scherrer Insti­tute was used [3]. W continuum at 35 KV, 10 mA, quartz sample support Ga internal standard were used for the me­dium Z elements whereas W tube at 20 KV and 15 mA, Cr internal standards and Plexiglas sample supports were used for Si and other low Z elements. As many elements are present in very low concentrations in ice a pre-concentra-tion step is required. Therefore a systematic study about the pre-concentration of the sample, instrumental stability and effect of excitation mode on sample analysis was made. The instrumental instability contributes to about 10% stan­dard deviation in the ppm concentration range. Detection limits for low atomic number elements were found in the ppm cone, range and for medium atomic number elements in the ppb cone, range. For the analysis 1-2 ml of melted ice mixed with 50-100 ul internal standard was evaporated to about 10-50 ul and transferred on sample supports in steps of 10 ul drying fast under an IR lamp in class 100 clean room conditions. Multielement standards (MES) were analysed first for vari­ous elements in range of Si (14)- Mo (42). Results were found to deviate up to maximum of 20% of the expected value. The error of the pre-concentration step was investi­gated by analysing MES. It amounted to 10% of the ex­pected value except for S. The higher deviation for S is because of high background and low analytical Une inten­sity. Therefore, for low Z elements instrumental parameters were changed to reduce the background as described ear­lier. Similar pre-concentration studies were made for the analysis of heavy elements e.g. U and Th and it was found

that method is not suitable for U and Th analysis in ice samples with present instrumental set-up. The recovery percentage observed by TXRF for Si and S analysed on Plexiglas sample support was within 30 % whereas for P it was within 52 % of the expected value. XRF signal for AlK a was very week making the analysis results unreliable. Based on this analytical procedure 14 ice samples were analysed for elements Si, P, S, K, Ca, Se, Ti, V, Cr, Mn, Fe, Co, Ni, Zn, Ga, Rb, Sr, Y, Zr, Nb and Mo. As these ice samples were earlier analysed for most of the elements by ICP-MS, results could be intercompared. Results of ele­ments like Ca and Mn with comparatively high concentra­tions in ice samples and moderate to high relative sensitivi­ties were comparable within an average of 30% (Fig. 1), whereas for the elements with low relative sensitivity or low concentrations the average deviation was higher. Thus TXRF method can be applied for the trace elemental analysis of Si (14) to Mo (42) in ice samples with variable degrees of precision and accuracy for different elements. For a good accuracy and precision either element should be present in at least few hundred ppb or its relative sensitivity should be high. For the elements Si, S, K, Ca, Ti, Fe and Zn the results may be expected to have a fairly good accuracy and precision with the present set-up, whereas for other elements errors involved may be larger. The method may serve as complementary to ICP-MS especially for analysis of elements Si, P and S. An efficient monochromatic exci­tation e.g. MoK a and CuK a may improve the results to a considerable extent

ACKNOWLEDGEMENTS Financial assistance from the ICSC-World Laboratory is gratefully acknowledged. Authors are thankful to Dr. F. Hegedues for his valuable suggestions.

REFERENCES [1] R.Klockenkamper, Total Reflection X-ray Fluores­

cence Analysis, Chemical Analysis Vol. 140, (John Wiley & Sons, New York 1996).

[2] N.L.Misra et al., Ann.Rep.Univ.Bern&PSI 2000, p.35. [3] F. Hegedues, Chimia 46, 477 (1992).

1500

1000

500

500 1000 Ca cone, (ppb) by ICP-MS

1500

DC X

6 8 10 12 14 16 Mn cone, (ppb) by ICP-MS

20

Fig. 1: Regression plots for Ca and Mn analysis by ICP-MS and TXRF in ice sample.

150

CEMENT CHEMISTRY: QUALITY CONTROL AND DEVELOPMENTS 2001

H.P. Zimmermann, M. Patorski, L. Döhring, M. Egloff (PSI)

This report gives a short summary of the projects and developments in our group during 2001.

As in the previous year most of the work was done in the field of product control for the Swiss nuclear power plants and PSI. We received 46 radioactive and 22 inactive sample-sets. So we performed about 200 compressive strength and about 1000 y-spectrometric measurements.

Additional sample-sets of incinerator ashes, solidified at PSI, have been taken for product control during the last cementation campaign. For specification purposes some samples of the pure ashes and filter materials were analysed with the method of prompt gamma-ray activation analysis by S. Baechler et al. of the Department of Physics of the University of Fribourg, as described elsewhere in this report.

Also a second sample-set of slag produced in the ZWILAG plasma incinerator was activated at SINQ (spallation induced neutron source) and the leaching, respectively the dissolution behaviour, was investigated. For the first set of slags with irregular surfaces S. Baechler et al., using neutron tomography, described elsewhere in this report, have determined the surface area.

The crushing of the graphite from the former research reactor DIORIT for solidification in cement has just started with the permission of the Swiss Federal Nuclear Safety Inspectorate (HSK) after some final demonstrations of the feasibility of the procedure.

Infrastructure

NAGRA

PSI Fig . l : Distribution of working capacity between our

customers. (KKW: all Swiss nuclear power plants).

On special request we performed measurements of the burning point of some bitumen samples. The burning point is defined as the temperature when a substance continues to burn for 5 sec after an initial ignition with an external source. Since, for the flash point measurements, we use a continuously closed cup system, it is not possible to use that equipment for the determination of the burning point, which requires an open cup system. Bitumen releases some 'white smoke' when heated and burns with lots of soot. So the methods used in oil and road construction industries according to international norms cannot be applied to radioactive samples due to the necessary amounts and the risk of contamination of the working place. The norm

procedures are contrary to the regulations for working with radioactive material.

Finally we found a possibility to do it with a semi-closed system, consisting of the small crucible from the flash point apparatus and a lid with a small chimney. The lid is pressed to the crucible, so the burnable fume is collected and can leave only through the chimney where it can be ignited with an external flame. The crucible is heated from beneath with a Bunsen burner and the temperature is measured inside the crucible with a thermocouple. This set up can work with small amounts, less than 0.5 g of bitumen matrix.

4 *

IIB

Fig. 2: Lid with chimney (inner diameter 5mm) and thermocouple, pressed to the crucible, with the external lighter system.

T a p

Fig. 3: Crucible with a small specimen before (left side) and after the measurement. The outer diameter of the top of the crucible is 5 cm.

ACKNOWLEDGEMENTS

We want to thank S. Baechler and his colleagues of the Department of Physics of the University of Fribourg for their spontaneous help and H.-U. Aebersold for the irradiations at SINQ/PSI.

151

PROMPT GAMMA-RAY ACTIVATION ANALYSIS OF ASHES FROM THE PSI-INCINERATOR

S. Baechler (Univ. Fribourg & PSI), J. Jolie (Univ. Köln), H.-F. Beer, M. Rüthi, S. Bajo, M. Egloff, M. Patorski, H.-U. Aebersold, E. Lehmann, H.P. Zimmermann (PSI)

Several ashes, resulting from burnable wastes from the Swiss nuclear power plants, PSI, and medicine, industry, and research were analyzed with PGAA.

INTRODUCTION

Until now, combustible wastes from the Swiss nuclear power plants, PSI itself, and from medicine, industry, and research, so-called MIF-waste, are burned in the PSI pilot incinerator facility (PVA). Then the ashes are solidified with cement in 2001-drums. The solidified waste packages from the power plants are sent back to the plant for interme­diate storage, the drums with PSI and MIF-ashes are stored in the federal intermediate storage facility (BZL) at PSI. It is required by the regulations of the Swiss Nuclear Safety Inspectorate (HSK), the Swiss National Cooperative for the Disposal of Radioactive Waste NAGRA, etc. to particular­ize not only the radioactive nuclides in the packages but also the main inactive (chemical) components should be specified. All the data are collected in a centralised data­bank at NAGRA but the specific data are also available in the power plants and PSI.

A thorough chemical analysis of the ashes was not always performed due to the necessary expenditure. Most analysis methods like ICP-OES, ICP-MS, ion chromatography etc require the total dissolution of the material. Due to the ra­dioactivity and the main inactive components the samples have to be diluted to be below the activity limits allowed in a non-radioactive laboratory and to avoid contamination of the apparatus by the inactive main components. Since the composition of the ashes varies quite a lot in dependence of the waste even the dissolution procedure may not work in any case. The use of prompt gamma-ray activation analysis (PGAA) with an existing set-up at PSI offered one possibility to circumvent these difficulties.

P R O M P T GAMMA-RAY ACTIVATION ANALYSIS

Prompt gamma-ray activation analysis (PGAA) is a non­destructive nuclear technique for measuring concentrations of various elements in a sample. The method consists in observing capture gamma-rays emitted promptly by a target material during neutron irradiation. PGAA is an important tool for analyzing light elements such as H, B, N, Si, P and S, which are usually difficult to measure by conventional neutron activation analysis (NAA). Furthermore, PGAA is highly sensitive to toxic elements as Cd and Hg and some rare earths, especially Sm and Gd. This technique is par­ticularly suitable for non-destructive multielement analysis of both major and trace components. For example, PGAA proved to be the most adapted technique for quantitative determination of H, B, Si, S, P, CI, Ca, Ti, Cr, Mn, Fe and Ni in minerals.

The PGA facility at SINQ has been built at the end of a cold neutron guide. The neutron beam interacts with the sample placed in a target chamber. Then, prompt gamma-rays are detected by a Compton suppression spectrometer, which is composed of a central Ge detector surrounded by NaI(Tl)/BGO scintillators. Finally, the detector is shielded

against neutrons and direct gamma radiation. The set-up has been described in more detail elsewhere [1].

The best-suited analytical method for accurate multielement PGAA is undoubtedly the ko-standardization developed by Molnár et al. [2]. So, this new approach has been success­fully tested at SINQ and can be applied at the moment for 26 elements of interest, including those above-mentioned. On the other hand, the ko-standardization yields only rela­tive elemental concentration. Absolute elemental concen­tration requires the determination of at least one element in the sample by using another analytical method. For this study, absolute concentrations were estimated by using a relative standard method for PGA based on standard refer­ence materials of comparable matrix and similar geometry.

The samples were ground to get a homogenous sample. Approximately 1 gram was encapsulated in Teflon and measured directly without further preparation during 6 hours irradiation time.

Table 1: Relative amount of the elements in several ash-samples. Results for Cd, Sm and Gd are given in ppm.

A-1 A-3 A-7 A-10 A-13 A-21 A-25 A-27 A-466 A-3144 Elem. M[%] M[%] M[%] M[%] M[%] M[%] M[%] M[%] M[%] M[%]

B 0.233 0.045 0.086 0.057 0.224 0.039 0.299 0.048 0.032 0.060 Na 0.8 1.855 0.4 1.3 0.7 1.5 0.8 0.3 0.9 0.8 Al 5.61 4.95 2.53 7.33 4.59 8.58 2.94 3.55 5.70 5.02 Si 14.1 25.2 28.6 12.6 6.4 11.8 17.1 5.4 8.8 9.6 P 0.8 0.5 0.9 0.7 S 0.540 0.272 0.104 0.707 0.215 0.551 0.093 0.199 0.397 2.636 CI 0.107 0.138 0.033 0.156 0.459 0.148 0.053 0.350 0.130 0.716 K 0.435 0.323 0.344 0.329 0.239 0.251 0.390 0.162 0.266 0.450

Ca 11.34 9.58 3.46 12.03 8.42 11.37 2.92 5.57 9.00 11.51 TI 3.949 2.025 1.579 1.578 4.233 1.287 2.013 3.546 1.801 2.636 Cr 0.368 0.243 0.122 0.312 0.339 0.337 0.385 0.518 0.395 0.165 Mn 0.08 0.10 0.11 0.17 0.11 0.18 0.14 0.11 0.27 0.08 Fe 7.35 8.04 10.58 15.78 8.87 16.94 12.33 10.13 25.54 5.88 Co 0.034 0.036 0.049 0.066 0.047 0.075 0.055 0.041 0.114 0.029 NI 0.185 0.076 0.085 0.132 0.554 0.081 0.073 0.277 0.173 0.067 Cu 0.43 2.94 1.24 3.01 13.08 3.50 0.93 25.33 4.04 0.37 Zn 1.26 1.55 0.60 1.71 5.32 1.37 8.60 11.31 2.22 1.67 Cd* 1.3 2.5 1.0 11.3 3.1 6.0 2.3 4.7 3.7 3.1 Sm* 1.0 1.0 1.0 0.8 0.9 1.1 16.9 Gd* 1.9 1.2 1.1 1.3 1.0 1.2 1.0 0.9 1.3 1.6 Sum 47.6 57.8 49.9 57.2 54.7 58.0 49.1 66.9 59.8 42.4

The errors of the relative amount for the different elements were between 0.3 and 50 % depending on the element, mostly less than 10 %. Conversion of the relative amounts of the pure elements to absolute masses of the correspond­ing oxides (except CI) and comparison of the calculated total mass with the sample weight showed a good agree­ment with deviations between -12 to +43 %, which was sufficient for practical use.

REFERENCES

[1] M. Crittin et al., Nucl. Instrum. Meth. A 449, 221 (2000).

[2] G. L. Molnár et al., J. Radioanal. Nucl. Chem. 234, 21 (1998).

152

DETERMINATION OF THE SURFACE AREA OF ACTIVATED SLAG SAMPLES

S. Baechler (Univ. Fribourg & PSI), J. Jolie (Univ. Köln), E. Lehmann, M. Patorski, H.P. Zimmermann (PSI)

Activated slag samples were investigated by cold neutron tomography at the PGA station at SINQ. The aim of this study was to measure accurately the surface area of these samples while working in a safe way. Indeed, neutrons have the unique capability to image the inner structures of samples even when surrounded by a lead shielding

INTRODUCTION The interim storage facility ZWILAG will produce with a plasma incinerator slags and metal out of the burnable waste from medicine, research and industry and cast that in moulds. For quality control of the final product in respect to final storage of radioactive waste, leaching tests are being performed on activated slag samples, according to the guidelines of the Swiss Nuclear Safety Inspectorate HSK. Of importance for the determination of the leaching rate is the accurate measurement of the surface area of the sample. This task appears arduous for a piece with an irregular surface geometry. The current method using a calliper is time consuming and not really precise. In addition, radio­activity restricts the handling of real samples.

Cold neutron tomography gives a good possibility to safely investigate radioactive slag samples encapsulated in a lead container. This technique provides images similar to the well-known X-ray tomography. Cross-sectional slices are computed from several radiographs taken at different orientations of the sample. The calculated images are then assembled together to display the whole object in great detail. However, the interactions of X-rays and neutrons with matter are fundamentally different. For example, lead is particularly opaque to X-rays but reasonably transparent to neutrons. Furthermore, cold neutrons, compared to ther­mal neutrons, have a lower attenuation coefficient for lead due to the Laue-Bragg scattering.

EXPERIMENTAL PROCEDURE The measurements were performed at the PGA station using the cold neutron tomography set-up [1]. The detection system was based on a neutron to visible light converter (6LiF/ZnS:Ag) and a 1280x1024 pixels CCD camera. The optical configuration yielded a field of view of 3.4x2.7 cm 2, corresponding to 26.5-nm pixels. First, the slag sample was tightly fixed inside a lead cylinder of 50 mm outer diameter and 5 mm wall thickness placed on a rotating table. The distance between the rotation center of the object and the detector was given by the radius of the container. At this distance of 2.5 cm, the divergence of the beam limited the spatial resolution to 0.5 mm. So binning 4 pixels in each direction on the CCD minimized the image size and re­duced the acquisition time without affecting the spatial resolution. A radiograph corresponded then to a 320x256 matrix of 106-um pixels. Finally, the object was rotated from 0° to 180° by discrete intervals of 0.9°, resulting in 201 projections.

The data reconstruction consisted in processing succes­sively horizontal slices of the object using an algorithm based on a filtered back-projection. This procedure has been described in more detail elsewhere [1]. The volumetric object generated by the stack of image slices was visualized by VGStudioMax 1.0. Then, a non-linear diffusion filter

was applied to the slices to remove noise while preserving the edges. Finally, a polygonal surface was extracted from the volumetric object by defining an iso-value. The quality and accuracy of the generated iso-surface depended strongly on the extraction value. The polygonal surface was calculated by tri-linear interpolation of the surrounding 3d-pixels values and then constructed by a triangle-mesh sur­face. Finally, the surface area of the object under study was determined by summing up the surface area of triangles forming the extracted shell.

RESULTS AND DISCUSSION The procedure was repeated for 7 different activated slag samples. The surface area of the sample N°l was also cal­culated accurately using the calliper method and only 1.5% deviations were found with the surface area that was meas­ured by neutron tomography. For the samples N°2 to N°7, the results differed within 3 to 16% deviations. In addition, for each sample, the volume bounded by the iso-surface was compared to the accurate measurement of the volume using mass and density. The obtained volumes agreed within 1-2% deviations and thus assessed the accuracy of the extracted polygonal surfaces.

Table 1: Results of surface area and volume for 7 activated slag samples (A= this work; B = comparative method).

N° Surface A [cm2] Surface B [cm2] Volume A [cm3] Volume B [cm3]

1 9.292 9.43 1.292 1.323 2 9.033 8.01 1.485 1.496 3 9.564 8.81 1.718 1.739 4 13.012 11.91 2.368 2.396 5 14.426 13.98 2.850 2.885 6 14.831 12.44 3.210 3.223 7 17.427 15.39 4.424 4.392

Fig. 1: Visualization of extracted polygonal surfaces using SolidView 3.55 for samples N° 4, 6 and 7.

REFERENCE [3] S. Baechler et al., to be published in Nucl. Instrum.

Meth. A, (2002).

153

PRODUCTION OF 53-d 7 Be FROM GRAPHITE WASTE TARGETS

U. Köster (CERN, Geneva), R. Weinreich, M. Argentini (PSI), H.W. Gäggeler (Univ. Bern & PSI)

The 7Be amount of 1-1011 Bq/g in dismounted graphite targets of PSI was sufficiently high for generating radioactive beams of up to 300 nA. It is usable for measurement of cross sections for solar neutrino production.

The nuclear capture reaction 7Be(p,y) 8B is of major importance to the physics of the sun and the issues of the 'solar neutrino puzzle'. It is assumed that this reaction might be the main source of the high energy solar neutrinos from the sun, and it was urgently recommended to re-measure the cross section of this reaction [1].

In some preliminary experiments, 7 Be was produced at CERN by irradiation of a graphite target with high energy protons. The target was connected to a laser ion source. By a two-step resonant laser ionization, a radioactive 7Be-beam was produced and was implanted into a copper matrix. Thus, a target with a total of 3-10 1 5 atoms could be obtained [2]. The measurement of the cross section suffered from the low number of 7 Be atoms; a target of 6-10 1 7 atoms was requested.

From radioactivity measurement of dismounted graphite targets used at PSI accelerator for production of muons, it could be concluded that these targets at end of irradiation are containing between 0.8 and 2.5-10 1 1 Bq/g 7 Be. This would easily met the requests of the CERN group for a more intense 7 Be beam and a corresponding strong target, even after a reasonable decay time.

In some tracer experiments, it was tried to remove beryllium from graphite by oxidative handling, followed by purification and refinement on a tantalum backing. This chemical treatment, however, proved to be a hard procedure using strong acids so that it was difficult to transform this procedure into a remote system which must be necessary for handling high activities.

In a target dismounted in September 2001 after a relatively short irradiation time, using a calibrated radiation protection dosimeter, 4-10 1 8 atoms or 6 1 0 1 2 Bq 7 Be were estimated, and it was concluded to destroy this graphite target and to use the graphite without chemical treatment for production of a 7 Be beam.

End of November 2001, this procedure was carried out, the graphite was grained in a hot cell and was filled into the CERN target holder. Preliminary investigations using this PSI waste material showed that a beam of > 300 nA 7 Be could be produced at CERN which was higher for the factor 10 4 than a beam used before. The mass composition of beryllium in this graphite could be determined; likewise hthium was found strongly enriched in 7Li which is produced by decay of 7 Be.

These experiments will be continued.

REFERENCES

[1] E. G. Adelberger et al., Rev. Mod. Phys. 70, 1265 (1998).

]2] M. Hass et al., Phys. Lett. B 462, 237 (1999).

154

EFFICIENT SEPARATION OF MONO-, DI- AND TRIVALENT CATIONS BY HIGH PERFORMANCE ION CHROMATOGRAPHY

R. Weinreich, S. Stallone (PSI)

Isocratic HPIC separation of mono-, di- and trivalent cations including all rare earth metals was elaborated for use in radioanalysis of accelerator waste.

For analysis of radioactive waste of accelerator materials, it is favorable to separate a maximum of components with minimum effort. Thus, in our analyses the strategy is fol­lowed to 'peel off the main components (with regard to both mass and radioactivity) from dissolved samples by classical methods and to separate the weakly radioactive residue by high performance ion chromatography (HPIC). Subsequently, the individual components may be measured by more sensitive methods up to accelerator mass spec­trometry.

In the HIPC separations, it could be referred to modular units which are in principle well-known. Due to the antici­pated simplicity of separations, special attention was paid to isocracy, i.e. during separation process, the conditions must not be changed, and the separations itself must be reliable. Three columns were utilized: (i) A L L T E C H Universal Cation, a weakly acid cation exchanger consisting of sili-cagel covered with polybutadiene/maleic acid copolymer, (ii) W A T E R S Spherisorb 5SCX, a strongly acid cation ex­changer consisting of silicagel covered by sulfonic acids, and (iii) H A M I L T O N PRP-X200, likewise a strongly acid cation exchanger consisting of a styrene-divinylbenzene copolymer covered by sulfonic acids.

Table 1: Optimum isocratic HPIC separation conditions for mono-, di- and trivalent cations.

Cations Column Elution Time duration*)

Alkali metals (Li, Na, K, Cs)

H A M I L T O N PRP-X2000**) 4 mM HN03 in 30 % methanol 14 min

Divalent cations (Be, Zn, Mn, Ca, Sr, Ba)

W A T E R S Spherisorb 5SCX 4 mM ethylenediamine/3 mM cx-hydroxyisobutyric acid/4 mM glycolic acid, pH 4.5

24 min

Trivalent cations (Sc and all rare earths)

W A T E R S Spherisorb 5SCX identical as used for divalent cations 60 min

*) Flow generally 1.5 ml/min **) The A L L T E C H Universal Column is also suitable for separation of alkali metals.

All separations were performed in analytical columns. They will be transferred stepwise to semi-quantitative conditions up to 1 mg carrier amounts.

155

DETERMINATION OF URANIUM AND PLUTONIUM IN SHIELDING CONCRETE

R. Weinreich, L. Wyer, S. Bajo, J. Eikenberg (PSI)

In shielding concrete, 239'240Pu was found in amounts of 26.4 mBq/g. This result may raise questions regarding the final disposal of used shielding material.

With regard to planned final disposal of radioactive waste, special attention must be paid to the presence of a-emitting radionuclides. In an earlier study, it was tried to measure a-emitters in several activated metals (copper, cast iron, steels) after their chemical separation by a-spectrometry, but the result was negative; the a-activity of this metallic waste remained below the error limit [1]. Concrete, on the other hand, contains uranium in the order of 2 ppm; thus it could be expected that shielding concrete might contain some amount of plutonium which can in principle be formed via the nuclear reaction

2 3 8 U(n,y) 2 3 9 Np (2.36 d) -> 2 3 9 Pu (2.41-10 4 a)

from secondary neutrons produced by interaction of protons with most target materials. The open question was the amount of 2 3 9 Pu.

During the reconstruction of the beam calibration target BX2 (beam stop in November 1998), which is installed at the back of the Injector II cyclotron and has been irradiated with 72 MeV protons, some samples of shielding concrete were taken, in both forward and staggered direction of the proton beam behind the target. In a demonstration sample which due to spacial relations should contain a relatively high amount of a-emitters, plutonium was tried to find.

The separation scheme was optimized in ASE [2]. First, a y-spectra was taken from original sample. Then, the concrete is dissolved in HN0 3 /HF, and uranium and the transuranes are separated by column chromatography using the resins BioRAD 1-X2 and U/TEVA (Eichrom. Illinois, USA. The radioactivity measurements were performed using an a-spectrometer equipped with ion-implanted silicon charged particle detectors. The chemical yields of uranium and plutonium likewise were measured by a-spectrometry of calibrated amounts of 70-a 2 3 2 U and 3.7-105-a 2 4 2 Pu, respec­tively. By this separation procedure, plutonium cannot be separated from americium and higher transuranes, but is was shown by calculations that these radionuclides are formed in 1/3 of the plutonium activity [3].

Table 1. Radionuclides in shielding concrete of the target station BX2, calibrated on end of bombardment.

nuclide half-life radioactivity (Bq/g)

M M n 312d 4090 1 5 2 Eu 13.3 a 2829 4 6 Sc 83.3 d 1410 6 0 Co 5.27 a 714 2 2 Na 2.6 a 433 1 3 4 Cs 2.06 a 380 1 5 4 Eu 8.8 a 343 1 3 3 Ba 10.5 a 16.9 239,240p u 2.4-10 4 a 0.0264 2 3 8 u 4.46-10 9 a 0.0172

Besides of the well-known Eu, which is formed by neu­tron activation of rare earth metals in concrete, 2 3 9 Pu was found. This result must be verified by further samples, even of concrete which was activated by neutrons produced by the 590 MeV beam.

REFERENCES

[1] M. Rüthi and J. Eikenberg, private communication (1999).

[2] C. Gann, Diplomarbeit 2000, PSI Report 00-04 (Sept. 2000).

[3] F. Atchison, private communication (1999).

156

DNA-SEEKING GADOLINIUM COMPLEXES FOR NEUTRON CAPTURE THERAPY (NCT)

C. Salt (PSI & Univ. Basle), A. Sezen, T. A. Kaden (Univ. Basle) R. Weinreich (PSI)

DNA-targeting gadolinium-labelled compounds were conceived and synthesized in the scope of their use as potential GdNCT agents with the characteristics of dual diagnostic and therapeutic probes.

1 INTRODUCTION

The gadolinium neutron capture reaction 1 5 7Gd(n,y)* 1 5 8Gd generates complex nuclear decay transitions inducing prompt y decay of up to 7.9 MeV accompanied by the emission of internal conversion electrons, mostly non-radiative cascade transitions resulting in the ejection of Auger- and Coster-Kronig electrons in the energy range of 41 keV and below. These Auger cascades display extremely complex energy spectra, are highly ionising over the short range of several tens of nanometers and therefore capable of intense radiochemical damage if emitted in close proximity of the DNA. Although the linear energy transfer (LET) of these atomic electrons is about 10-25 keV/um, their simultaneous action may simulate high-LET-type biological damage, comparable with the effects of densely ionising a particles of high LET. The target cancer cell structure for GdNCT (gadolinium neutron capture therapy) is the DNA (deoxyribonucleic acid) which represents the genome and genetic fingerprint of the cell.

2 DRUG DESIGN

The design of an efficient GdNCT agent [1] must include the following key components:

3 FLUORESCENCE SPECTROSCOPY

The idea is to retain the DNA-seeking properties of the fluorophore while it is burdened with the gadolinium complex. Hopefully, also the altered gadolinium complex (with one DNA-targetting side chain) will not suffer too severe a destabilization as to loose the toxic gadolinum cation. Also, the association of two molecule types, fluorescence stain and gadolinium contrast agent must be sufficiently stable in order to arrive at the NCT target as one entity when navigating living cell sytems to accomplish its projected mission as DNA-destroying GdNCT agent.

350 i -r-

SPECTROSCOPIC »OLUTLON* BUFFERED AT PH 6 .8 300 -

H na r h a . - n O T A H r n m n IB y I n R R 3 C C O 5 0 n n

emiss ion wavelength [n m ]

< H l OKon iOKK

The DNA-seeking part of the molecule is a chromophore with fluorescent dye properties (fluorophore) such as the fluorescent cell stains and DNA minor-groove binders Hoechst 33258 and 33342 (Fig.l). The gadolinium ion is tighly held by a bifunctional chelating agent with the dual purpose of forming a stable gadolinium complex and a covalent bond with the DNA-targetting fluorescence stain.

H

1) R = H Hoechst 33258

2) R = CH2CH3 Hoechst 33342

Fig. 1: DNA-binding fluorescence stain Hoechst.

The gadolinium chelate moiety of the drug is based on the classic MRI (magnetic resonance imaging) contrast agents Magnevist and Dotarem the biodistribution and biocompatibility properties of which are well-documented.

Fig. 2: Fluorescence emission spectra: the titration of a potential GdNCT agent with plasmide DNA producing fluorescence yield enhancement which is evidence for DNA-binding [1].

The DNA binding properties of minor-groove binders can be assessed via the fluorescence yield enhancement as a function of the dye/DNA ratio (Fig.2). The dramatic fluorescence yield enhancement upon plasmid DNA titration is attributable to the tight binding of the fluorophore within the DNA minor-groove, where the excited state of the stain remains shielded from the water molecules of the aqueous medium and hence from non-radiative decay processes of the excited state causing losses in the fluorescence yields. The measured resultant fluorescence enhancement is taken as a DNA binding indicator and indirect proof of a binding event upon complex formation between fluorescence stain and DNA. In conclusion, the functionalization of the derived Hoechst­type chromophores with MRI-contrast agents does not noticeably interfere with the DNA binding properties of minor-groove binders. Therefore, the prospective GdNCT agents satisfy the foremost requirement of bringing the gadolinium atoms to the target structures prior to neutron irradiation.

REFERENCE

[1] C Salt: DNA-seeking gadolinium complexes for Neutron Capture Therapy (NCT), PhD thesis, and references therein, University of Basle 2001.

157

L a b o r a t o r y f o r I o n B e a m P h y s i c s

158

LABORATORY FOR ION BEAM PHYSICS

M. Suter (ETHZ & PSI)

In our laboratory, ion beam techniques are used as analytical tools to measure concentrations of rare cosmogenic nuclides in environmental samples as well as elemental compositions of various materials. Ion beams are also used to modify materials (electrical, optical and mechanical properties). For our research, two electrostatic accelerators facilities are available:

1 ) 6 MV van-de-Graaff Tandem accelerator from HVEC

2) 0.6 MV pelletron type tandem accelerator from NEC

Our main research area is accelerator mass spectrometry (AMS). This method is one of the most sensitive techniques to measure cosmogenic nuclides and trace elements in concentrations of 10"8 to 10"15 in mg size samples. This corresponds to detection limits of about 10 4 to 1 0 n atoms. The technique is most suited for the detection of long-lived radioisotopes such as 1 0 Be(t 1 / 2 = 1.5 Ma, 1 4 C(t 1 / 2 = 5730 a), 2 6 Al(t 1 / 2 = 716 ka) and 3 6 Cl(t 1 / 2 = 301 ka), which are produced in the atmosphere and in the earth's surface by cosmic rays, hence the name "cosmogenic nuclides". These nuclides play an important role in the environmental and in the earth sciences. They can be used as natural tracers to monitor transport phenomena in the atmosphere and the oceans. Under special conditions, they can be used for dating. We recognize an ever-increasing interest in these methods for research related to climate and anthropological history as manifested in our contributions of this annual report.

Most of the operating time of the tandem accelerator is assigned to the above mentioned activities. Our technical and scientific staffs invests a major part of their effort into the operation and the maintenance of the instrumentation to guarantee the success and the quality of the collaborative national and international research undertaken at this user facility.

The users pressure for higher performance of our analytical techniques, such as higher precision, higher sensitivity and larger flexibility of the instruments. At the same time, costs should be reduced and faster turnaround should be achieved. To answer these demands, we have a research program on instrumental developments, which allows us to play a leading role in this field of ion beam techniques.

To succeed with the new developments, it is essential to understand the physics involved. Most important is the understanding of collisions of atomic or molecular ions with a target (atoms or molecules in materials of different densities) as well as the formation, transport and the detection of ions. This includes the following processes:

1) Small angle scattering in a screened Coulomb potential.

2) Charge changing processes in collisions. These processes determine the average charge of the projectile and the fractions of the various charge states.

3) Stability of molecules in collisions when molecular ion beams are utilized.

4) Stopping processes in matter including statistical fluctuations. This is of importance for the detection and identification of ions.

5) Ion optics. It describes the transport of ion beams in electric and magnetic fields and is essential for the design of accelerators and mass spectrometers.

6) All the processes related to the beam formation in ion sources.

Many of these processes are complex (multiple electron processes) requiring a large database of experimental data. The data combined with simplified models is then the basis for modelling and designing new instruments or for the improvement of existing components.

In recent years, we have concentrated our activities to study the possibility of making smaller and simpler AMS arrangements. In collaboration with the accelerator building company National Electrostatic Corp. (NEC), we have developed the first AMS facility for radiocarbon dating operating at energies below 1 MeV. Meanwhile, NEC has developed a commercial version of this prototype. In 2001, the first two AMS systems based on the new concept have been delivered to customers. They have successfully passed acceptance tests and are now in operation for dating, clearly demonstrating the potential of the new concept we had developed.

We continue these studies to extend the new techniques to other long-lived radioisotopes. Successful tests with 2 6 Al, 4 1 Ca, 1 2 9 I have been performed. Reasonable transmission values have been achieved, but the background is generally about one order of magnitude higher than what is achievable with our larger accelerator system. Further research is in progress to reduce this background.

One of the highlights of last year's technological research program was the first detection of Pu isotopes with our small AMS facility. At the time this facility was designed, it was not anticipated that actinides could ever be analyzed with such small AMS systems. Therefore, the magnets of our system were not laid out to bend these heavy masses. Only with reduced ion source and accelerator potentials could these experiments be performed. The great success of this achievement is due mainly to a guest scientist, Keith Fifield from Australian National University, who spent a three months sabbatical at our laboratory.

159

THE PSI/ETH TANDEM ACCELERATOR FACILITY

H.-ASynal, M.Döbeli, I.Hajdas, C. Kottler, P.W. Kubik (PSI); G. Bonani, M. Grajear, S. Ivy-Ochs, C. Maden, R. Mühle, J. Santos, Ch. Schnabel, M. Stocker, M. Suter, S. Tschudi (ETHZ)

The 2001 operation of the PSI/ETH tandem accelerator at ETH Hönggerberg is summarised in a detailed compilation of beam time allocation, of AMS sample statistics for the radioisotopes measured and of the major fields of research.

Hours % Samples 1999 2000 2001 1999 2000 2001 1999 2000 2001

AMS Be-10 373 503 555 13.7 17.0 18.5 1187 1664 1456 C-14 842 1039 834 30.9 35.1 27.9 1768 2055 1721

Al-26 48 129 109 1.8 4.4 3.6 83 259 161 Cl-36 313 127 264 11.5 4.3 8.8 623 275 649 1-129 103 169 198 3.8 5.7 6.6 327 415 538

Heavy Elements 99 49 94 3.6 1.7 3.1 12 23 25 Subtotal 1778 2016 2054 65.2 68.1 68.6 Materials Sciences 357 265 330 13.1 8.9 11.0 Accelerator SIMS 193 400 210 7.1 13.5 7.0 Tests 57 90 145 2.1 3.0 4.8 Conditioning 344 191 253 12.6 6.4 8.5 Total 2729 2962 2992 100 100 100 4000 4691 4550

Beam time statistics 1999-2001

Research Field Be-10 C-14 Al-26 Cl-36 1-129 Total Oceanography 130 93 223 5% Ice Core samples 468 360 66 894 20% Limnology 17 43 60 1% Atmosphere 200 94 57 122 473 10% Environmental Monitoring 26 26 1% Exposure Age Dating, Others 196 152 55 103 144 650 14% Earth Sciences (Total) 1011 382 55 520 358 2326 51% Meteorite/Cross Sections 58 58 17 133 3% Archaeology 446 446 10% Others, Tests 71 620 6 24 63 784 17% Subtotal 129 1066 64 24 80 1363 30% Standards 210 200 27 67 74 578 13% Blanks 106 73 15 38 26 258 6% Total 1456 1721 161 649 538 4525 100%

Compilation of measured AMS samples at the PSI/ETH AMS facility in 2001

Last year, the PSI/ETH tandem accelerator was running for 2992 hours. In December 2001, operation was stopped due to a defective charging belt. Suitable charging belts are not available commercially anymore since the company has ceased its belt production. However, we managed to obtain a new belt and we will be able to start accelerator operation again at the end of January 2002. The total number of analysed samples last year was 4550 making 2001 the second most successful year since routine AMS began at PSI/ETH in 1982. The beam time devoted to the various research fields has not changed much compared to 2000. 69 % of the total beam time was used for A M S applications, 13% for tests and accelerator conditioning

and the remaining 18% were available for materials research. For 3 6C1, the number of samples measured has more than doubled and for 1 2 9 I the number of analysed samples has increased by as much as 30%. This was due to several new projects in connection with mid-latitude ice core archives. The new small AMS system for radiocarbon dating was used for routine dating measurements as well as for studies of fundamental processes in the AMS technique at low beam energies. For the first time, thorium, uranium and plutonium isotopes were measured with overall efficiencies being higher and detection limits being comparable to measurements conditions at large accelerators.

160

MEASUREMENT OF PLUTONIUM ISOTOPES WITH THE ZURICH 0.5 MV AMS SYSTEM

K. Fifield (Australian Nat. Univ.); M. Suter (ETHZ; H-A. Synal (PSI)

First measurements of plutonium have been made with the Zurich 0.5 MV AMS system. For terminal voltages between 200-300 kV, a surprisingly high stripping yield of 20-25% for ions in charge state 3+ has been observed. A sensitivity of 9 to 75 fg has been accomplished for the different plutonium isotopes. It is limited by background events, predominantly from interfering molecular break-up products.

Ultra-sensitive detection of plutonium isotopes using an accelerating voltage of only 300 kV has been demonstrated with the small AMS system at ETH, Zurich, which is based on an NEC 0.5 MV tandem pelletron accelerator.

The methodology was similar to that developed at the Australian National University at higher energies. Briefly, the plutonium was dispersed in an iron oxide matrix, and PuO" ions were generated in the 40-sample MC-SNICS ion source. After pre-acceleration to 20 keV, the ions were mass-analysed by a 5.5 amu-MeV magnet, and accelerated to the terminal of the accelerator operating at 300 kV. Here, they were stripped in a 45cm long gas stripper containing argon with an equivalent thickness of 0.2 ug/cm2. After the second stage of acceleration, ions in the 3 + charge state with an energy of 1.2 MeV were analysed by the achromatic high-energy spectrometer, which consists of 90° magnetic and electric analysers. The 32 amu-MeV mass-energy product of the magnet imposed the 300 kV limitation on the terminal voltage. After analysis, the plutonium ions were counted in a silicon detector.

Table 1: Detection limits of the different plutonium isotopes.

Isotope Detection limit (fg)

Number of atoms (10 7)

2 3 9 Pu 8.5 2.1 2 4 0 Pu 25 6.3 2 4 2 Pu 8.5 2.1 2 4 4 Pu 75 18

Energy spectra at the 2 4 0 Pu settings from the silicon surface-barrier detector for standard and blank samples are shown in fig. la. The energy resolution for the 1.2 MeV plutonium ions is about 45%, and is dominated by scattering and straggling in the 40 ug/cm 2 gold contact on the front surface of the detector. Background arises predominantly from '^Dy 2* and 8 0 S e 1 + ions which have essentially the same m/q and mE/q2 as the ^ P u 3 * ions and hence follow the same trajectories through the high-energy spectrometer. A comparison between the background in fig. la and the spectra in fig. lb indicates that both species contribute. Clearly, the resolution of the detector is insufficient to resolve completely the 2 4 0 Pu from the 1 6 0 Dy ions, although a window, which selects 50% of the former, accepts only 10% of the latter. Backgrounds for 2 3 9 Pu and 2 4 2 Pu are substantially less because the interfering ions do not have

exactly the same m/q and hence are much better separated by the high-energy spectrometer. In fact, even in the 2 4 0 Pu case, the 1 6 0 Dy and 2 4 0 Pu ions are separated by ~lmm at the detector position due to the small atomic mass differences, but at present this is insufficient for a separation of the two species. Table 1 lists the current background-limited detection limits for the four long-lived plutonium isotopes. Clearly, a detector with better resolution would eliminate most of the background, and further studies on alternative detection systems are planned.

# 1 5 0 0

0 1 0 0 0

«21500 c 3

0 1 0 0 0

500

b A f%

8 0 S e , \1 V6°D y

50 100

Channel Number

150

Fig. 1: (a) Energy spectrum of 1.2 MeV 2 4 0 P u 3 + ions from a standard sample containing 5pg of 2 4 0 Pu per mg of iron. Also shown is the background spectrum from a sample of blank iron oxide taken under the same conditions and for the same time, (b) Spectra of 1 6 0 Dy and 8 0 Se ions of the energy of the 2 4 0 Pu ions.

Transmission measurements of these 3 + ions were investigated using macroscopic beams of thorium, injected as ThO. The ions transmitted were analyzed with the high-energy magnet as a function of stripper gas pressure. At higher pressure, the shape of the curve is determined by scattering of the Th ions from the argon atoms in the stripper, and has an exponential dependence on pressure. The 3 + charge state fraction is obtained by extrapolating this exponential dependence to zero pressure. A surprisingly high yield of -20-25 % was found.

161

TIME-OF-FLIGHT DETECTION IN SUB-MEV ACCELERATOR MASS SPECTROMETRY

M. Stocker (ETHZ); M.Döbeli, H.-A. Synal (PSI); M. Suter (ETHZ)

The new PSI/ETHZ 500 kV accelerator mass spectrometer was upgraded with a high-resolution time-of-flight spectrometer to improve the detection limits for radionuclides such as 26Al and 4 1 Ca.

In its first version the final detection system of the new 0.5 MV AMS facility consisted of a simple Si surface barrier detector. In order to allow for an independent velocity measurement, a time-of-flight spectrometer was added in front of the Si detector. The combined energy and velocity information makes mass identification possible. This can help to suppress the background from scattered stable isotopes present in e .g . 2 6 Al or 4 1 Ca measurements.

m

• H

4 » 4 * * *

Fig. 1: Stop detector of the electrostatic mirror type. The Si surface barrier detector is below the triangular mirror of the channelplate detector.

The time-of-flight spectrometer consists of a start and a stop detector of the electrostatic mirror type [1]. The stop detector is displayed in Fig. 1. The length of the flight path is 47 cm. Many of the technical details can be found in reference [2].

1000

800

600

400

200

0

" A I "A l

I \ 2000 4000

Time [ps] 6000 8000

Fig. 2: Time-of-flight spectrum of 2 6 Al and scattered 2 7 Al at 1 MeV.

In order to reduce energy straggling in the start detector, a diamond-like carbon foil of only 0.5 tig/cm2 was used. This also significantly reduces the angular straggling responsible for efficiency losses in the case of low energy heavy ions.

In order to investigate the timing properties, the detector has been tested with 1 MeV protons. For these fast and light particles energy straggling, angular straggling and the energy spread of the beam are insignificant. A time resolution of (221 + 4) ps and an efficiency of about 30% was obtained.

The discrimination performance of the new detection system was analysed for 1 4 C/ 1 2 C, 2 6A1/ 2 7A1, 4 1Ca/ 4 0Ca, and i 2 9 y i 2 7 j p a r t j c i e s j n m e c a s e 0 f aluminum at 1 MeV the two isotopes are separated by 3.3 ns. The peak width is 0.72 ns (Fig. 2). Scattered 2 7 Al particles can now be suppressed by almost 2 orders of magnitude. In the case of 0.8 MeV calcium, a peak separation of 3.0 ns is obtained (Fig. 3) resulting in a suppression factor for scattered 4 0 Ca of about 20.

3000

2500

2000

1500

1000

500

0

• Cq40 A CG41

A

.i - i 0 1000 2000 3000 4000 5000 6000 7000

Time [ps]

Fig. 3 : Time-of-flight spectrum of 4 1 Ca and scattered 4 0 Ca at 0.8 MeV.

As a conclusion it can be stated that the upgrade of the 0.5 MV AMS system by a time-of-flight spectrometer allows the suppression of scattered stable isotope ions of medium-heavy nuclei by 1 to 2 orders of magnitude.

REFERENCES

[1] F. Busch et al., Nucl. Instrum. Meth. 171, 71 (1980).

[2] M. Döbeli et al., Nucl. Instrum. Meth. B 142,417 (1998).

162

RADIOCARBON DATES OF OLD AND MIDDLE KINGDOM MONUMENTS IN EGYPT

G. Bonani (ETHZ); I. Hajdas (PSI); W. Wölfli (ETHZ); H. Haas (USA); M. Lehrter (Semitic Museum, Harvard Univ.); R. Wenke (Univ. of Washington); Z. Hawass, S. Nakhla (Supreme Council of Antiquities, Cairo)

Between 1984 and 1995, over 450 organic samples were collected from monuments built during the Old and the Middle Kingdom. The purpose was to establish a radiocarbon chronology with samples from secure context and collected with the careful techniques required for radiocarbon samples. This chronology is compared to the historical chronology established by reconstructing written documentation.

Radiocarbon dating of dynastic monuments in Egypt goes back to the very beginning of this dating method. W. F. Libby included three Old and Middle Kingdom samples in his initial set of known-age samples as a test of the method [1]. In the following twenty years, numerous laboratories have followed Libby's lead and analyzed similar samples. From the published results it became apparent that close agreement with the historical chronology was often lacking. A closer study of this disagreement was needed. The American Research Center in Egypt (ARCE) undertook in 1984 the first of the two projects reported here with financial support from the Edgar Cayce Foundation. The Foundation's interest in the project rested on a hypothesis offered by Cayce that the Giza pyramids dated to 10,500 BC.

The Giza pyramids are memorials to 4 t h Dynasty rulers whose reigns are placed by Egyptologists to around 2500 BC. Our project therefore concentrated mostly on the Old Kingdom. The results [2] confirmed the sequence of the monuments and their ages as they were established by historians, but the match between 1 4 C and historic dates was only approximate and left open the possibility of a difference between the two chronologies. It became clear that more data was needed. Thus a second project was begun in 1995. It was designed to confirm or adjust the difference between the two chronologies. David H. Koch who established the Pyramids Radiocarbon Dating Project provided support for this second project.

In the field we looked for organic materials that were clearly linked to the construction of the monuments. Temples and pyramids built with mud bricks yielded grass, straw and reed fragments, which had been mixed into the clay and soil before shaping the bricks. Finding suitable materials in stone monuments was of a greater challenge. In most of these monuments the stone building blocks were leveled and secured in place with mortar that was manufactured locally. This required massive fires to heat gypsum or limestone. The roasted minerals and the ashes from the fires were added to the mortar mix along with remaining charcoal fragments. These usually very small fragments (1-2 mm) constituted the datable material. While searching the monuments we examined seams between stone blocks for mortar filling and for black specks of charcoal inside the mortar.

44 samples were large enough for conventional radiocarbon dating by liquid scintillation counting (LSC) first at Southern Methodist University (Dallas, Texas, USA) and

later at Desert Research Institute (Las Vegas, Nevada, USA) [3]. 226 small samples were dated with AMS at the PSI/ETH AMS laboratory in Zurich [4].

Figure 1 shows the calibrated monument ages, l a errors were used with the averaged monument dates and each calibration range is displayed. The length of a solid black bar corresponds to the BC time span, and the width of the bar is proportional to the statistical weight of the range. For comparison, the historical chronology of the monuments is shown as hatched rectangles. Applying 2a errors to the monument ages results in wider time spans but does not significantly alter observed differences between the two chronologies.

i r n i 1 1 1 1 1 i 1 1 1 1 1 * •

m

- 7

3 4 0 0 3200 3 0 0 0 2B00 h I i I i I i I i I i I i I i I i I i

2600 2 4 0 0 2 2 0 0 2000 1B00 1600

BC

AMENEMHET IH P y r . SENUSRET I I P y r a m i d QAKARE IBY P y r a m i d PEPE I I P y r a m i d

— TET1 P y r a m i d UNAS T o m b A

— UNAS P y r a m i d UNAS T e m p l e SAHURE T e m p l e QUEEN'S P y r a m i d USERKAF P y r a m i d

— USERKAF T e m p l e SHEPSESKAF MENKAURE P y r a m i d KHAFKE P y r a m i d DJEDF.FP.E P y r a m i d DJEDRFRE T e m p l e KHUFU P y r a m i d

— GIZA L o g i s t i c C e n t e r MEIDUM P y r a m i d DASHUP, P y r a m i d T o m b 17 SEKHEMEHET DJOSER T e m p l e

— DJOSER P y r a m i d e — T o m b 3505 — T o m b 3035

T o m b 3 5 0 4 T o m b 3 4 7 1 T o m b 3357

Fig. 1: Comparison of the calibrated l a C ranges (horizontal black bars) with the historical chronology of the monuments (hatched areas). The lengths of the solid black bars corresponds to the BC time span, and their width is proportional to the probability to find the true age within the corresponding l a range.

REFERENCES

[1] J.R. Arnold et al., Science 110, 678 (1949).

[2] H. Haas et al., BAR International Series 379, 585 (1987).

[3] H. Haas et al., in : Liquid Scintillation Counting and Organic Scintillators, edsH. Ross, J.E. Noakes, J.D. Spaulding, Chelsea, Michigan : Lewis Publishers Inc., 669 (1991).

[4] G. Bonani et al., Nucl. Instrum. Meth. B29, 87 (1987).

163

REFINED RADIOCARBON CHRONOLOGIES AND A CORRELATION BETWEEN CLIMATIC RECORDS

/. Hajdas (PSI); G. Bonani (ETHZ); J. McManus (WHOI); M. Mendelson, S. Hemming (LDEO)

Studies of past climates play a key role in the understanding of present and future climate variability. Time frames of such changes are of great importance for paleoclimatic reconstruction. Based on high-resolution radiocarbon dating, we propose a correlation between wet periods in the western United States and the record of an enhanced transport of ice-rafted debris, so-called Heinrich Events, into the North Atlantic.

During the last 40,000 years, Earth experienced numerous climate fluctuations. Detailed studies show that changes from a cold to a warm climate (and vice versa) occurred in a very short time. For example, the cold spell of the Younger Dryas 12,000 years ago appears to have 'settled in' during 30-50 years based on ice core studies. Such resolution of dating is exceptional and cannot be achieved for most of the records and events. However, reliable chronologies can be established using different methods of dating. 1 4 C dating is the most common among those applied in Quaternary studies of the last glacial period and déglaciation period. The first radiocarbon chronology of Heinrich Events has been published by Bond et al. [1]. Although these radiocarbon ages, which were obtained using AMS 1 4 C dating of foraminifera shells, are well established, obtaining solid chronologies beyond 14,000 BP (Heinrich Event 2) might be difficult. The radiocarbon time scale is complicated due to variations (an increase) in atmospheric 1 4 C content between 40,000 and 35,000 BP. An apparent inversion in 1 4 C ages occurs shortly before (and possibly even during) Heinrich Event 4 (Fig. 1). In this study we propose that this 1 4 C 'event' can be used as a global marker in correlations between paleo-records. Two sites, the deep-sea sediment from the North Atlantic core ODP-984 south of Greenland and the Wilson Creek formation from Mono Lake, California, USA, were 1 4 C dated and correlated.

The deep-sea core provides records of Heinrich Events. These are seen as layers characterized by low content of biogenic carbonate and an increase in detrital carbonate. We have dated planktonic foraminifera shells found in those layers. Some 1000 to 2000 shells of N.Pachyderma(s) were needed for 1 4 C AMS analysis. The radiocarbon chronology of the ODP-984 core shows an excursion in 1 4 C ages, which precedes the ice-rafted debris peak corresponding to Heinrich Event 4 [2]. This is in agreement with a finding by Voelker et al. [3] who had shown a similar feature in the record of another North Atlantic core (PS-2644). Ostracode shells from the section of Wilson Creek were dated using 1 4 C AMS. At least 50% of the shells' outside surface were removed prior to the dating. The 1 4 C excursion is observed between 90 and 120 cm above the base. Our conclusion is that the section of sediment between 120 and 200 cm corresponds to Heinrich Event 4 (Fig 1).

Based on a radiocarbon age model, Benson et al. [4] proposed a correlation between dry events (lake lowstands LI through L4) and Heinrich Events (HI through H4), respectively. However, the L? lowstand event remained uncorrelated (Fig 2). According to our chronology the L? event, which has been recognized between 120 and 150 cm

above the base, corresponds to Heinrich Event 4. Therefore L4 event, which is observed between 20 and 46 cm above the base and is older than 40,000 BP, might correspond to Heinrich Event 5.

WILSON CREEK FORMATION MONO LAKE,CA

25000 ' I . . » .1 • • • I 300 250 200 150 100 50

Height (cm)

Fig. 1: Radiocarbon chronology of Wilson Creek

Hight (m)

Fig. 2: Proposed correlation between climatic events in Mono Lake (CA, USA) and the North Atlantic region. Periods of low lake level have been correlated to Heinrich Events in the North Atlantic [4].

REFERENCES

[1] G. Bond et al., Nature 365,143 (1993).

[2] I. Hajdas et al., PSI Sei. Rep. 2000/1.

[3] A. Voelker et al., Radiocarbon 42, 437 (2000).

[4] L.V. Benson et al., Quaternary Research 49 ,1 (1998).

164

USES OF C-14 DATA IN A TRANSECT OF MID-ATLANTIC RIDGE

B.Renik, W.S. Broecker (LDEO); I. Hajdas (PSI); G. Bonani (ETHZ)

Twenty deep-sea cores recovered across the Mid-Atlantic Ridge were studied. Radiocarbon ages at sediment depth of ca. 50 cm were measured in order to establish pattern of sedimentation rates.

The strength of the ocean's conveyor circulation during glacial time is not clear. In particular, paleo-proxies present conflicting evidence as to the conveyor's influence over the composition and ventilation rate of Atlantic deep-water [1]. Our study will examine this circulation by comparing glacial and Holocene data from 1 4 C, Nd, Ô13C, ô 1 8 0 , Cd, and Zn measurements on a series of cores traversing the western flank of the Mid-Atlantic Ridge (MAR) between 45 °N and 45°S.

The first step in this work is to outline the stratigraphy of each core, so that the glacial and Holocene sampling depths may be identified. To elucidate the age-depth relationship in the sediment, we made bulk accelerator mass spectrometric (AMS) 1 4 C measurements at about 50-cm depth on each core. These data help us in three ways.

First, the 1 4 C dates will enable us to locate the glacial portion of the sediment. Most immediately, they say whether it begins above or below 50 cm. Then, by reflecting the average net sediment accumulation rate over that 50 cm, the data give a sense of how far from that depth we can find the target glacial samples (20 to 16 kyr BP 14C-years old). We are in the process of refining this stratigraphy by conducting profiles of carbonate content in the top 80 cm of each core. Although the rise in carbonate content should signal the change from glacial to Holocene sediment, we have found that this transition is not always obvious and that the 1 4 C dates at 50 cm are useful in anchoring our interpretations.

Second, the sedimentation rates calculated from the C data have improved our understanding of the core-top stratigraphy. We measured the difference in foraminifera ô 1 8 0 between 50-cm depth and the core tops to confirm that this segment straddles the glacial-to-Holocene change. (Measurements were made by Athanasius Koutavas, Linda Baker, and Jean Lynch-Stieglitz of LDEO.) In some cores, the difference between the ô 1 8 0 values was too small for the core tops to be pure Holocene sediment (Fig 1). The 1 4 C data helped explain these results by revealing low sedimentation in most of these cores. This suggests that Holocene sediment was bioturbated with older material to produce the intermediate ô 1 8 0 core-top values.

Third, the 1 4 C results reveal a latitudinal pattern in sediment accumulation rate (Fig 2). It peaks around the equator and the higher-latitude ends of the transect, and drops off between them. This symmetric pattern seems worthy of investigation, and our carbonate content measurements may give a sense of whether it is regional variation in carbonate or silicate flux that is shaping this bulk sedimentation pattern.

n r 8 1 8 0 ALONG MAR TRANSECT

"i r T

cf •

i — i 1 r r

J L _!_

O „ ï 0.

50 40 30 20

2.0

1.5

1.0

,5

J L

- # - DEEP, Gr.(T.)Trunc.

— DEEP, GsSacc. - O - - T 0 P , Sr. (T.)Trunc.

- TOP. Gs. Sacc.

X -10 -20 -30 -40 -50

I I I I I I 1 1 1 - • - DEEP-TOP Gr. (T.) Tome.

-t— DEEP-TOP, Gs. Sacc.

- \ > ^ \ • - \\\ \ / ~ * ' 1

\ 4 V > -1 1 1 * 1 1 1 1 1 1

0.0

-0.5

50 40 30 20 10 0 -10 N LATITUDE

-20 -30 -40 -50

S

Fig. 1: ô 1 8 0 along the MAR transect. Foraminifera of different species were taken at about 50 cm ("deep") and at the top of the core ("top"). The upper panel shows the ô 1 8 0 data of the different foraminifera species. The lower panel depicts the difference of ô 1 8 0 in the top of a core and in a depth of 50 cm.

g | 2

00 cocooxo

45

N 5 EQU. 5

LATITUDE

Fig. 2 : Bulk average net sedimentation rate along MAR transect. AMS 14C-dated samples were taken at about 50 cm depth. Water depth (in km) of each core site is Usted at the top of the figure.

REFERENCE

[1] W.S. Broecker, Israel Journal of Geochemistry, in press (2002).

165

CONSERVATIVE BEHAVIOR OF 1 0 Be IN WATER MASSES OF THE ANTARCTIC CIRCUMPOLAR CURRENT

M. Frank (ETHZ); M. M. Rutgers van der Loeff (AWI Bremerhaven); P. W. Kubik (PSI); A. Mangini (Heidelberger Akademie der Wissenschaften)

The first detailed transect of water column profiles across the Antarctic Circumpolar Current (ACC) shows that 10Be behaves as a conservative water mass tracer even in an environment of high biological productivity and thus high particle fluxes. This is mainly a consequence of the rapid water mass advection and mixing within the ACC.

The behavior of particle reactive cosmogenic 1 0 Be in the oceans (residence time -500-1000 years) has been subject to numerous studies. Effects of particle scavenging (removal by adsorption to particles) versus advective transport by water masses compete in controlling the 1 0 Be concentrations in the ocean. We present the first set of water column 1 0 Be concentrations on a transect between the Weddell Sea (low particulate fluxes) and the ACC (high biological particle fluxes) (Figure 1).

The data of all profiles show an increase in concentration from very low values in the surface waters to up to 2000 atoms/g in the deep water below 1000 m. Gradients are much steeper at the southerly stations at the AWB and the Weddell Sea. The 1 0 Be distribution at the four northern stations clearly mirrors the influence of North Atlantic Deep Water (NADW) with its typical concentration of around 800-1000 atoms/g. The well mixed deeper waters further south are dominated by a water mass called Circumpolar Deep Water (CDW) with higher 1 0 Be concentrations largely coming from the Pacific Ocean. This distribution is obviously not significantly influenced by 1 0 Be contributions to the surface waters coming from melting Antarctic ice.

Polar Frontal Antarctic Zone Zone

7 0 0 0 -I 1 I

50 52 54 56 58 Degrees Southern Latitude

It is well known that the surface water masses north of the Antarctic Wedell Gyre Boundary (AWB) are areas of high biogenic opal productivity and thus high particle fluxes which scavenge 1 0 Be out of the water column [1, 2]. This apparently contradicts the conservative behavior indicated by our data. The highly dynamic hydrography of the ACC can, however, explain the observed profiles. The ACC is the ocean's largest current in terms of volume transport, and water mass residence times are short. This short time does only allow a depletion of the uppermost 500 m where residence times of 1 0 Be amount to only a few months. Particle remineraUsation and water mass exchange at greater depth are too rapid and efficient to allow any significant increase above the values expected for the different water masses.

These results imply that the adsorptive flux of 1 0 Be reconstructed from the sediments of the ACC can indeed be related to past variability of boundary scavenging and thus intensity and composition of particle flux in the past, if the rapid water mass exchange has supplied 1 0 Be constantly to each location of the ACC. A prerequisite to this assumption is, however, that the supply and admixture of NADW has remained approximately unchanged in the past to maintain a constant supply of 1 0 Be. This may not have been fulfilled for the glacial periods of the Late Quaternary when the supply of NADW was diminished and CDW was probably more dominated by Pacific water masses with higher 1 0 Be concentrations. As a consequence, the enhanced glacial 1 0 Be deposition rates recorded by the sediments below the ACC may at least partly originate from higher 1 0 Be supplies rather than increased scavenging induced by higher particle fluxes.

REFERENCES

[1] N. Kumar et al., Nature 387, 675 (1995).

[2] M. Frank et al., Paleoceanography 15, 642 (2000).

Fig. 1: Dissolved 1 0 Be concentrations (atoms/g) for a water column transect between 46°S and 62°S in the eastern Atlantic sector of the ACC. AWB marks the approximate position of the ACC Weddell Gyre Boundary. The morphology of the sea floor appears to be steep due to the inclusion of two more westerly located stations, one of which is at the deep South Sandwich Trench.

166

PALEOCEANOGRAPHY IN THE NORTH PACIFIC OCEAN

T. van de Flierdt, M.Frank, A.N. Halliday, B.Hattendorf, D. Günther (ETHZ); J. R. Hein (USGS); P.W. Kubik (PSI)

Time-series for two North Pacific ferromanganese crusts were dated with mBe/)Be ratios and analysed for their Pb isotope composition. Our data show a clear change in provenance ofPb isotopes in the North Pacific Ocean during the past 15 Ma, which are probably related to changes in ocean circulation.

Records of deep-ocean trace metal isotope composition can be retrieved from pristine seawater precipitates, such as hydrogenetic ferromanganese crusts. These crusts have very slow growth rates (1-10 mm/Ma). Long-term isotope time-series of trace metals obtained from those ferromanganese crusts are suitable to reconstruct past changes in ocean circulation and source provenance.

Crusts RNDB06 13D-27A and S6-79-NP D4-13A were recovered from the north-west and the north-east Pacific (51°27.8'N, 167°38.2'E and 53°32.6'N, 144°22.4'E) at water depths of 1800-1500 m and 2100 m, respectively. Profiles of these 56 mm and 41 mm thick crusts were taken to obtain chronologies based on the decay profile of 1 0 Be / 9 Be ratios (tl/2 = 1-5 Ma) (Figure 1). Growth rates of 5.7 mm/Ma and 2.6 mm/Ma have been determined.

1.00E-6

A RNDB06, NW Pacific growth rate: 5.7 mm/Ma

+ D4-13A, NE Pacific growth rate: 2.6 mm/Ma

CD

CD

1.00E-7

1.00E-8 r

1.00E-9 20 30

depth [mm]

Fig. 1: 1 0 Be/ 9 Be ratios for two North Pacific crusts. By combining AMS 1 0 Be concentrations and ICP-MS 9 Be concentrations, reliable growth rates can be obtained.

Lead isotopes were analysed with high precision using a Nu Plasma Multiple Collector Inductively Coupled Plasma Mass Spectrometer (MC-ICP-MS). The external reproducibility was obtained by repeated standard measurements (NBS981) and is < 150 ppm for all Pb ratios.

The two crusts show variability in deepwater 2 0 6 Pb/ 2 0 4 Pb over the past 10-15 Ma that exceeds the amplitude of the so far known Equatorial Pacific records about threefold (Figure 2). Both crusts display monotonie evolutions, which are very similar to each other even though the sample locations are separated by more than 3000 km along the Aleutian island arc.

Q.

Q.

18.85

18.75

18.65

18.55

Fe-Mn Deposits:

A NW Pacific

• NE Pacific

10 15 20

a g e [ M a ]

25 30

Fig. 2: 2 0 6 p b / 2 0 4 p b v e r s u s a g e for N o r t h p a c i f i c

ferromanganese (Fe-Mn) crusts. Shown for comparison are data from Equatorial Pacific crusts [1,2] .

The source terrains for Pb in North Pacific deepwater are local island arcs. The present day Pb isotope signature of both Fe-Mn crusts is exactly the same as that of volcanic rocks from the Aleutians. The lower values in 2 0 6 Pb/ 2 0 4 Pb of 10 to 15 Ma ago are due to a stronger influence of the Northwest Pacific arcs, e.g. Honshu and Kamchatka. Continental material (wind-derived Asian loess) is traceable at the locations of the crusts, but plays a minor role. The similarity of the records points to a very efficient mixing of deepwater along the Aleutian arc in a local convection cell. This cell has shown only limited exchange with deepwater from the Equatorial Pacific.

The trend in the two isotope records is caused by changes in importance and mixing proportions of the local endmembers (Aleutian arc, Northwest Pacific arcs and Asian loess). This can either be due to changes in circulation patterns or the continental rocks preferentially weathered. Our preliminary interpretation is a weakening of the Western Boundary Current during the past 15 Ma. This current flows along the western margin of the Pacific Ocean and carries material from the western arcs to the Aleutian region. As its strength was decreasing, the closest local source (Aleutians) became more prominent.

REFERENCES

[1] H. F. Ling et al., Earth Planet. Sei. Lett. 146, 1 (1997).

[2] K. David et al., Chem. Geol. 178, 23 (2001).

167

RECONSTRUCTION OF THE EARTH'S MAGNETIC FIELD INTENSITY OVER THE LAST 200 000 YEARS, BASED ON 1 0 Be RECORDS IN DEEP-SEA SEDIMENTS

M. Christi, C. Str obi, A. Mangini (Heidelberg Academy oj'Sciences); P.W. Kubik (PSI)

The intensity of the Earth's magnetic field is reconstructed from 10Be fluxes into deep-sea sediments. A simple box model is able to describe boundary scavenging of 10Be in the ocean and can be used to separate transport and production signals in single 10Be records.

The cosmogenic radionuclide 1 0 Be is produced in the upper atmosphere by galactic cosmic rays impinging on the Earth's atmosphere inducing spallation reactions in N and O atoms. Due to the shielding effect, the 1 0 Be production rate varies inversely with the intensity of the Earth's magnetic field. Therefore, 1 0 Be records in deep-sea sediments were suggested as archives for the reconstruction of the geomagnetic field intensity [1]. However, climatic influences on the 1 0 Be deposition could modulate the production signal. The biggest argument against 1 0 Be as a good tracer for the Earth's magnetic field is that it reacts very sensitively to transport processes in the ocean. We use a new approach to separate transport and production signal of 1 0 Be in deep-sea sediments. First, lateral transport of adsorbed 1 0 Be (sediment redistribution) is quantified by normalizing to thorium excess ( 2 3 0TheX). Then, lateral transport of dissolved 1 0 Be is calculated using a simple box model. Vertical sediment accumulation rates are used as input values for the model calculations. The calculated scavenging correction factors are applied to correct the records for boundary scavenging. The correction procedure [2] was applied to four 1 0 Be records located of the Atlantic and Pacific Ocean (Table 1). Details will be published soon.

Tab. 1: 1 0 Be records used for this study with location, water depths and references.

core, location depth [m] ref. PS 2082, Southern Ocean 4610 [3] M 16772, Equatorial Atlantic 3913 [4] GEO B 1523, CearaRise 3292 [1] RNDP 74P, Central Pacific Ocean 2547 [5]

The model corrected Be records are used to calculate relative variations of the geomagnetic field intensity (Fig. 1). In the upper part of the figure, the record is compared to a 1 0 Be derived paleointensity stack [1]. Within the uncertainties the two 1 0 Be derived records look very similar, which is remarkable, because calculating the stacked record is much different from the procedure we applied here. There is also a good correlation with the NAPIS-75 record [6] based on paleointensity records from North Atlantic sediment cores (lower left of Fig. 1). Furthermore, we observe a good correlation with the magnetic field record based on 3 6C1 and 1 0 Be concentration in the GRIP ice core [7] (lower right of Fig. 1).

10 20 30 40 50 60 70 80 0 10 20 30 40 50 60 70 80

Age [ka] GISP timescale Age [ka] GISP timescale

Fig. 1: Geomagnetic field intensity record (thick Unes). Other paleointensity reconstructions (dotted Unes) based on global 1 0 Be stack data [1], NRM/ARM data in North Atlantic sediment cores [6] and 3 6C1 and 1 0 Be concentration in the GRIP ice core [7]. The gray areas show the calculated uncertainties.

CONCLUSIONS

A simple box model describing boundary scavenging of 1 0 Be in the ocean is used to calculate correction factors, which are then appUed to correct the 1 0 Be records to be used in the calculation of a paleointensity record. This 1 0 Be based paleointensity record correlates well with other records from very different archives.

REFERENCES

[1] M. Frank et al., Earth Planet. Sei. Lett. 149, 121 (1997).

[2] M. Christi et al., Eos Trans. AGU 82(47), Fall Meet. Suppl., Abstract OS21D-12, (2001).

[3] M. Frank,

Bericht z. Polarforschung AWI186, 136 (1996).

[4] W. Henken MelUes, Ph.D. Thesis, ETH Zürich ( 1990).

[5] B. Schwarz, Ph.D. Thesis, Univ. Heidelberg (1996).

[6] C. Laj et al., Phil. Trans. Royal Soc. London A 358, 1009 (2000).

[7] G. Wagner et al., Nucl. Instrum. Meth. B 172, 597 (2000).

168

STATUS OF RADIONUCLIDE MEASUREMENTS IN THE ICE OF THE SOUTH INILCHEK GLACIER (KYRGHYZSTAN)

H.-A. Synal (PSI); D. Cecil, J.Green, D. Naftz (USGS); J. Santos (Univ. Seville); J. Beer (EAWAG); K.Kreutz (Univ. Maine); C. Wake (Univ. New Hampshire); V.B. Aizen ( College of Mines and Earth Resources, USA)

The long-lived radionuclides 36Cl and 137Cs are measured in a deep ice core recovered from the South Inilchek Glacier in the Tien Shan Mountains. Using the 36Cl bomb pulse and the 1963 time marker of elevated 137Cs, we could establish a preliminary time scale and derive average accumulation rates for the past 50 years.

Ice cores are unique archives preserving information on past climate changes. Most important are the polar ice sheets where precipitation of several hundreds of thousands of years is conserved. But mid-latitude Alpine glaciers can play an important role by connecting information from polar sites with observations made at regions where 80 percent of the human population H ves.

The U.S. Geological Survey (USGS) is conducting a collaborative isotopic research program on mid-latitude glaciers around the world. Form one of the studied glacier sites, the Inilchek Glacier located in the Tien Shan Mountains on the borders of Kyrghyzstan and Kazakhstan, two deep ice cores have been recovered during a field campaign in 2000. A part (100 m) of the first core (167 m total length) has been prepared in the field for the analysis of the radionuclides Cl, I and Cs. Be measurements are planned depending on the quality of the ice archive. The ice allocated to the measurements of the radionuclide records was shipped to Zurich, and samples have been processed for the analysis with AMS. The 3 6C1 measurements have been completed in 2001. 1 2 9 I measurements are in progress and 1 3 7 Cs measurements have been made for about 40 of the 100 ice core samples. The 3 6C1 and the 1 3 7 Cs results are shown in figure 1.

shows an anomaly between 4 and 9 meter water equivalent (m.w.e.) right at the location of the high 3 6C1 concentrations.

1940 1950 1960 1970 1980 1990 2000 Year/AD

Fig. 1: Profiles of 3 6C1 and 1 3 7 Cs in the ice core recovered from the South Inilchek Glacier in the Tien Shan Mountains (42°N, 80°E). For comparison, also the 3 6C1 profiles from Dye-3 (Greenland) and Guliya (Himalayan) are shown.

Four peaks of elevated 3 6C1 concentration can be observed in the first 20-m of the core. Most probably, these excursions are due to avalanche events causing the influx of older snow/ice from the mountain peaks surrounding the glacier plateau. Evidence of avalanche debris is found in the ice. In addition, a <5180 profile of the first 10 m of the core

« -30

-dl80(%ovsmow) -36Cl/g

400 600

core depth / craw.e.

Fig. 2: Profiles of ô 1 8 0 and 3 6C1 from the upper 10 m.w.e. of the first core. Anomalies in both parameters indicate an avalanche layer.

The primary objective of our work, to establish time markers of fallout events from the nuclear weapons tests in the 1950's and 1960's is accomplished. The 3 6C1 concentration record shows a pronounced peak with concentrations almost three orders of magnitude higher than the base line. This is similar to the observations from Dye-3 in Greenland. It can therefore be expected that the deeper core between 20 and 85 m.w.e. is undisturbed. The deepest part of the core analyzed so far does not reach into the pre-bomb era. It is planned to extent sampling to also get the per-bomb 3 6C1 levels and the increasing slope of the bomb peak.

Using the well dated Dye-3 record as a reference together with the 1 3 7 Cs bomb horizon, a time to depth relationship for the Tien Shan ice core can be made, from which the snow accumulation rate can be derived. For the last 50 years, the average accumulation corresponds to about 1.9 m.w.e. However, the amount of additional snow input due to avalanches is difficult to estimate and can result in a deviation to the true snow accumulation. But because two distinct time markers in the 1950's and 1960's are available, accumulation in that time range should vary only within tight limits. Thus, it seems that the accumulation rate in this part of the core is somewhat higher than in the younger section of the core.

The high snow accumulation rate at the Inilchek glacier reveals new feature of the 3 6C1 bomb fallout. From 1962 to 1964 we observe a peak, which could have been caused by enhanced local fallout from nearby test sites.

169

RECONSTRUCTION OF THE PALEO ACCUMULATION RATE OF CENTRAL GREENLAND USING Be-10 AND Cl-36

3. Beer, G.Wagner, R. Muscheler (EAWAG); H.-A. Synal, P.W. Kubik (PSI)

The snow accumulation rate is one of the most fundamental climate parameters, which can to be derived from ice cores. In addition to its importance to the climate, it provides a crucial constraint on depth-age scales, where annual layer counting is not possible. We have derived the accumulation rate for the time interval 3-75 ka BP by applying a method based on the cosmogenic radionuclides 36Cl & 10Be in the Summit ice cores and on geomagnetic field data.

Usually the reconstruction of the accumulation rate of an ice sheet is based on parameters with a clear seasonal signal (e.g. Ô 1 80) and on ice flow models. In the case of the GRIP and GISP ice cores, which are only 30 km apart, significant discrepancies of up to a factor of 2 were found [1,2] .

Our approach for deriving the accumulation rate is based on the connection between the relative accumulation rate (À), the concentration (c) of the cosmogenic radionuclides 3 6C1 or 1 0 Be in the ice and the flux of 3 6C1 or 1 0 Be (F) from the atmosphere into the ice:

MD) •

we show the calculated accumulation rate (relative values) for the measured 1 0 Be and 3 6C1 concentrations [5].

F(D) c{D)

Hence the accumulation rate can be calculated as a function of the depth D in an ice core, if the paleoflux F(D) of the radionuclides can be independently evaluated, which is actually the crucial point.

The flux of the cosmogenic radionuclides at any location of the Earth's surface depends on the interplay between two processes: the production rate in the atmosphere and the transport from the atmosphere into the ice. 3 6C1 and 1 0 Be are produced in interactions of cosmic ray particles with constituents of the atmosphere (O, N and Ar atoms). Their production rates vary inversely with the Earth's magnetic field intensity and with solar activity [3], both of which modulate the cosmic ray flux penetrating into the atmosphere.

We assume now that the local 3 6C1 and 1 0 Be flux in central Greenland represents the mean global production rate, and we assume that on time scales longer than 250 years only the geomagnetic field leads to variations in the production and therefore in the flux of 3 6C1 and 1 0 Be. Hence all data used for calculating the accumulation rate is low-pass filtered with a cut-off frequency of (250 yr)"1. In view of all these assumptions, we estimate the uncertainty of our reconstruction to be in the range of 15-20%. To calculate the paleoproduction rate of 3 6C1 and 1 0 Be, we use a new reconstruction of the geomagnetic field intensity for the interval 0-75 kyr, which is largely based on NAPIS-75 (North Atlantic Paleolntensity Stack since 75 kyr BP) [4]. Besides an estimation of the paleoproduction rate of 3 6C1 and 1 0 Be, the radionuclide profiles of 3 6C1 or 1 0 Be are needed in order to derive the accumulation rate at Summit (see formula above). We use an almost complete 3 6C1 record covering the time interval between approximately 17.5 and 75 kyr BP. The flux F is derived from the geomagnetic field reconstruction using the relationship between geomagnetic field intensity and production rate [3], which is assumed to be proportional to the radionuclide flux to Summit. In Fig. 1

1500

Depth [m]

2000 2250 2400 2500 2550

30

10

-based on magnetic field & Be-10 data -based on magnetic feld <k CI-36 data

10 20 30 40 50 60

Age [kyr BP]

70

Fig. 1: Upper panel: reconstructed accumulation rates based on geomagnetic field data and on 3 6C1 and 1 0 Be data. Lower panel: Ratio between our and Johnsen et al.'s accumulation rate [5].

The upper panel of Fig. 1 shows the reconstructed accumulation rate based on the geomagnetic field intensity and on the 3 6C1 and 1 0 Be data. In the lower panel our data are compared with the accumulation rate derived by Johnsen et al. [1]. Up to about 60 ka BP, our and Johnsen et al.'s reconstructed accumulation rates agree very well.

The main advantage of our approach is that it is independent of ice flow models. Our approach can therefore be applied to much older ice where the thinning effect prevents the identification of annual signals.

REFERENCES

[1] S. J. Johnsen et al., Tellus 41 B, 452 (1989).

[2] K. M. Cuffey and G. C. Clow, J. Geophys. Res. 102 26383 (1997).

[3] J. Masarik and J. Beer, J. Geophys. Res. 104, 12099 (1999).

[4] C. Laj et al., Phil. Trans. R. Soc. Lond. A 358, 1009 (2000).

[5] G. Wagner et al., Earth, and Planet. Sei. Lett. 193, 515 (2001).

170

VARIABILITY OF 1 0 Be & 3 6C1 IN RECENT ANTARCTIC SNOW AND AIR SAMPLES

M.Huke, AStanzick, D. Wagenbach (Univ. Heidelberg); H.-A. Synal, P.W. Kubik(PSI), J. Kipfstuhl (AWI Bremerhaven); M. Legrand (LGGE Grenoble)

First36CI measurements in Antarctic air samples together with other data from shallow firn cores at Antarctic deep-drilling sites show distinct changes in chloride deposition processes for snow accumulation ranging from about 3 to 6 cm-water- equivalent (cm.w.e.).

Attempts to elucidate the recent spatial and temporal behaviour of 1 0 Be and 3 6C1 in the northern parts of Central Greenland have been finalised [1]. Meanwhile, we have extended the investigations to Antarctica with special emphasis on the European deep-drilling positions -Dome C (DC: 74.5°S, 123.0°E), Dronning Maud Land (DML: 75.0°S, 0.1°E), Berkner Island (BI: 79.6°S, 45.6°W)- and the German overwintering station Neumayer (NM: 70.7°S, 8.3°W).

Compared to the North Greenland study area, the snow accumulations at the drilling sites are comparable (BI) and up to a factor of four lower (DC). Neumayer Station, where we already have established a decadal 7Be-aerosol record, provides our reference site for atmospheric year-round observations of 1 0 Be and 3 6C1.

The main activities of the program were: • High volume aerosol (and atmospheric HCL) sampling

during summer campaigns at DML and DC as well as year-round sampling at NM for analysis of cosmogenic isotopes along with aerosol chemistry and 2 1 0 Pb.

• Analyses of firn core records of 3 6C1 and 1 0 Be at BI, DML and DC for the last approximately 70 years along with dedicated snow pit sampling (for analyses similar to atmospheric samples).

At NM, aerosols were sampled since 1998 on precleaned cellulose filters (A-Filter). To retain HCl we used a backup filter impregnated with an alkaline solution (B-Filter). 3 6C1 was measured for the years 1998 and 1999 on pooled filter aliquots, each pool representing 3 months. A- and B-Filters were measured separately. For the 1998 season, 97% of chloride was retained on impregnated (gas) filters. Between 29% (winter) and 53% (summer) of the total 3 6C1 was found on the gas filters, while or 1999, these fractions were only 10%-20%, possibly due to an unusual low collection efficiency of the backup filters.

Combining the A-Filter data from both years and using the B-Filter data from 1998 only, we estimate the annual mean atmospheric 3 6C1 concentration to be 1250 atoms/m3, whereas when using all data a lower limit of 1050 atoms/m3

results.

For Central Antarctica (DML and DC), where data also possibly suffered from a too low collection efficiency of the backup filters, lower limits for 3 6C1 concentrations are 300 atoms/m3 for DML and 3000 atoms/m3 for DC. As both filter sets have been prepared identically, the one order of magnitude difference between this two locations is not a collection artefact but reflects a significant difference in

boundary layer air concentrations (not seen in the levels).

u Be

10 6 -, Dome C

DML

Berkner Island

10 5 J

10 4 .

10° 2000

Fig. 1: 3 6C1 records for three Antarctic firn cores with different accumulation rates (dating of the DC and DML firn cores is preliminary). BI: 13.7 cm.w.e./a, DML: 6.2 cm.w.e./a and DC: 3 cm.w.e./a. 3 6C1 in

36r firn from BI and DML reflects the bomb- CI input function [2] and recent values are equal to prebomb values. In contrast to this finding, bomb- 3 6Cl at DC is present up to the snow surface.

This surprising result is mirrored in the near surface 3 6C1 firn levels as well. We found similar 3 6C1 bomb signals at BI and DML (Fig. 1) despite a factor of two difference in accumulation rates. We conclude that remobilization of chloride is not very important down to 6 cm.w.e./a. However, modern 3 6C1 levels at DC are clearly a factor of 20 higher while accumulation rates are only another factor of two lower than in DML. This suggests the presence of bomb- 3 6Cl at the surface and in the boundary layer at DC and therefore remobilization effects for chloride, which are strongly dependent on accumulation rates. This could make it difficult to use 3 6C1 in Antarctic areas with very low snow accumulation rates.

We plan to use 1 0 Be data to further analyse the air-firn transfer in situations of low accumulation range to assist the interpretation of the ongoing European deep-drillings in Antarctica.

REFERENCES

[1] A. Stanzick, Dissertation Univ. Heidelberg (2001).

[2] H.-A. Synal et al., Nucl. Instrum Meth. B 52,483 (1990).

171

EXPOSURE AGE OF LATE GLACIAL AND EARLY HOLOCENE MORAINES IN THE FERWALL GROUP, AUSTRIAN ALPS

H. Kerschner (Univ. Innsbruck, Austria); S. Ivy-Ochs (ETHZ); R. Sailer (Univ. Innsbruck, Austria); P.W. Kubik(PSI)

10Be surface exposure dating ofEgesen Stadial moraines in the Ferwall group supports a Younger Dry as age of the moraines. Younger moraines (Kartell Stadial) seem to have been deposited during the early Preboreal.

The general downwasting of alpine glaciers after the Last Glacial Maximum was interrupted by a number of successively smaller re-advance periods ("stadials"). Among them, the "Egesen Stadial" could be correlated to the Younger Dryas (Greenland Stadial 1) [1]. It is usually three-phased, pointing to at least three major phases of glacier advance during the Younger Dryas. After the deposition of the youngest Egesen moraines and before melting back to a Holocene (Little Ice Age: LIA) order of magnitude, many glaciers formed moraines which are situated downvalley from the Holocene moraines, but clearly higher up than the youngest Egesen moraines. Traditionally they were attributed to the Kromer / Kartell stadial [2, 3], whose age, however, is unknown.

The drop in the equilibrium Une altitude (ELA) of a glacier advance can be a valuable indicator for the precipitation during the advance provided that the change in summer temperature is known with a sufficient degree of accuracy [4]. If glacier advances are sufficiently well dated, they can be used to reconstruct palaeo-precipitation fields.

It was therefore attempted to date a possible Egesen Maximum moraine in the Ferwall Group mountains at the western fringe of the Austrian Central Alps. The moraine is situated in the Schönferwall Valley a few kilometers to the southwest of St. Anton am Arlberg (Fig.1). The ELA drop was -290 m relative to the LIA ELA. Three samples have been analyzed so far. PreUminary 1 0 Be exposure ages range between 12,700 and 10,700 years supporting the assumed Younger Dryas age of the moraine complex. This also supports the morphostratigraphical correlation of moraines in the vicinity with the Egesen Maximum advance.

Fig. 1: Study areas in the Ferwall Group, Austria

The type locality of the Kartell stadial is situated in the Moostal valley in the Ferwall Group a few kilometers south

of St. Anton am Arlberg (Fig. 1). The moraines are situated about 1 km downvalley from the LIA moraines and about the same distance upvalley from the youngest local Egesen moraines. They show some post-depositional deformation due to rockglacier flow. The ELA drop was -120 m relative to the LIA ELA. Three samples were analysed and gave preliminary 1 0 Be exposure ages ranging between 9,400 and 10,500 years cal BP. This indicates that the moraine was stabilized shortly after 11,000 cal BP. The data show that during the early Preboreal, glaciers in the Ferwall Group re-advanced to an extent, which was substantially larger than LIA. Whether the Kartell advance was caused by an increase in accumulation after the rather dry final phase of the Younger Dryas or by a temperature drop such as the Preboreal Oscillation [5, 6] remains unclear.

REFERENCES

[1] S. Ivy-Ochs et al., Eclogae Geol. Helv. 89, 1049 (1996).

[2] G. Gross et al.,

Zeitschr. Gletscherkd. Glazgeol. 12, 223 (1977).

[3] R. Fraedrich, Düsseldorfer Geograph. Stud. 12 (1979).

[4] H. Kerschner et al., Ann. Glaciol. 31, 80-84 (2000).

[5] B. Ammann, Palaeo3 159, 191 (2000).

[6] S. Björck et al., J. Quat. Sei. 12,455 (1997).

172

l u Be EXPOSURE DATES FOR THE IRCH HILL MORAINE SYSTEM, SOUTH ISLAND, NEW ZEALAND

S. Ivy-Ochs (ETHZ); C. Schlüchter (Univ. Bern); P.W. Kubik (PSI); G. H. Denton (Univ. Maine)

10Be surface exposure dating of six boulders from the Birch Hill moraine complex at Lake Pukaki implies advance of glaciers in the Southern Alps during the time corresponding to the northern hemisphere Younger Dryas.

There are several moraines in the Southern Alps (New Zealand) which have been suggested to have formed by the advance of glaciers around the time of the Pleistocene-Holocene transition (post Otiran or post-Last Glacial Maximum). This was based on sparse radiocarbon dates, as well as géomorphologie data (e.g. [1], [2] and references therein). This includes the Waiho Loop moraine, the Misery Lake moraines and the Birch Hill moraine complex. The Waiho Loop moraine located on the west side of South Island was formed after 11,050 1 4 C years [3] based on radiocarbon dates from wood found underneath the till. The Misery Lake moraines at Arthur's Pass have been exposure dated at 11,900 years [4] (recalculated with recent 1 0 Be production rates [5,6]).

The Birch Hill moraine system (Figure 1) comprises several spectacular steep walls found along both sides of the Tasman Valley just north of Lake Pukaki. The lateral moraines extend for tens of kilometers and are up to a hundred meters high. The moraines and ice-decay features are covered with huge boulders many more than 5 m high. Boulder lithology ranges from fine- to medium-grained greywackes of the Torlesse Sandstone to phyllites of the Haas Schist. We have measured 1 0 Be concentrations in eight of these boulders. The calculated exposure ages show a bimodal distribution. Ages for six of the boulders range from 10,900 to 13,000 years, while two boulders have ages of 20,000 and 25,000 years.

The two 'older' boulders lie on the outermost part of the Birch Hill moraine complex, one on the orographic left side, one on the right. Evidence from both sides of the Tasman Valley indicate that the Birch Hill glacier plowed into and overran the older Pukaki deposits (Last Glacial Maximum equivalent) (e.g. [7] and recent mapping). These two older boulders may really belong to the Pukaki deposits, i.e. are external to the Birch Hill moraine zone. Another possibility is that they were simply pushed into the Birch Hill moraine from the underlying Pukaki deposit without turning, so that the same side remained up and exposed. A third possibility is that the boulders are peeking through a window in the Birch Hill deposit into the underlying Pukaki deposits. Either way they provide further temporal information about glacier movements in the Pukaki region during the LGM (see Schäfer et al., this Annual Report).

From the ages of the six boulders in the younger group an unweighted average of 12,000 years can be calculated. This falls within the Younger Dryas chronozone as recorded in Greenland ice (which lasted roughly from 12,800 to 11,600 years ago). In comparison, the age of the Misery Lake moraines at Arthur's Pass is 11,900 years. The glacier advance, which led to the formation of the Waiho Loop

moraine, took place after 12,800 cal years ago. Glacier advance synchronous with the Northern Hemisphere Younger Dryas has now been verified at three sites on the South Island, New Zealand. This provides further evidence that right around 13,000 to 12,000 years ago, a significant cold event did affect much of the planet. In that case, neither the forcing nor signal-transference mechanism have been unequivocally pinpointed.

Fig. 1: The Birch Hill lateral moraine complex (left of center). Lake Pukaki is in the background.

REFERENCES

[1] C. J. Burrows et al., Boreas 5, 57 (1976).

[2] S. J. Fitzsimmons, Quat. Int. 38/39, 69 (1997).

[3] G. H. Denton and C. H. Hendy, Science. 264, 1434 (1994).

[4] S. Ivy-Ochs et al., Geog. Ann. 81 A, 313 (1999).

[5] P. W. Kubik et al., Earth Planet. Sei. Lett. 161, 231 (1998).

[6] B. Heisinger and E. Nolte, Nucl. Instrum. Meth. 172, 790 (2000).

[7] C. J. Speight, NZ J. Geol. Geophys. 6, 160 (1963).

173

STRUCTURE OF THE LAST GLACIAL MAXIMUM IN SOUTHERN MID-LATITUDES: TERRESTRIAL EVIDENCE FROM NEW ZEALAND

/. M. Schäfer (IDEO), S. Ivy-Ochs (ETHZ); U. Ninnemann (LDEO); R. Wieler (ETHZ); P.W. Kubik (PSI); G. H. Denton (Univ. Maine); P. Schlosser (LDEO); C. Schlüchter (Univ. Bern)

Dating of moraines in the Southern Alps of New Zealand using cosmogenic 10Be indicates a period of glacial highstand during the Last Glacial Maximum (LGM) over almost 10 ka before the final LGM collapse about 18 ka ago. The LGM termination in southern mid-latitudes appears to be strikingly synchronous to northern mid-latitudes suggesting a rapid transport mechanism of the underlying climate signals, i.e. atmospheric transport.

Global reconstruction of the termination of the LGM and its transition to the Holocene is a key task to understanding the processes that drive the Earth's climate. Records focusing on this subject are mostly derived from polar ice cores and their interpretation is still controversial (e.g. [1] versus [2]). We investigate the structure of Late Glacial mountain glacier advances in New Zealand (NZ), a small island in southern mid-latitudes near Antarctica, and compare them to other mid-latitude records. We date the moraine set at Lake Pukaki, Southern Alps, using in-situ cosmogenic nuclides and intend to match the results with data from offshore high accumulation sediment cores that are expected to record the glacial melt water pulse at the end of the LGM. Our approach tackles the questions (i) How was the timing of the LGM in southern mid-latitudes compared to other mid-latitude sites in both hemispheres, and (ii) Is the structure of the LGM in New Zealand similar to nearby Antarctica as recorded in ice cores?

The Lake Pukaki (Southern Island, NZ) setting is shown in Fig. 1. Both, terminal and lateral moraines at Lake Pukaki are very well preserved. Moraine sets from adjacent glacial lakes display a very similar setting. We sampled greywacke erratics, separated quartz, and analyzed for in-situ cosmogenic 1 0 Be and 2 6 Al. All rocks are several m 3 in size. This excludes post-depositional snow cover and turning. The process of erosion can also be excluded due to preserved glacial striae on the sampled surfaces.

The investigated sediment core VM122-16 is located some 20 km offshore from the main melt water drainage of the East Coast of New Zealand. We analyzed oxygen and carbon isotopes in planktic and benthic foraminifera. Because the 1 4 C dating of this core is not yet completed, we concentrate here on the terrestrial data. The prehminary results are shown in Fig. 1. The "outermost moraine" of the LGM was deposited 27,800 + 2,500 years ago, whereas the exposure age of the lake moraine, deposited just before the lake forming collapse of the "mountain glacier LGM" in New Zealand is 18,000 + 2,000 years. This implies:

(I) The termination of the LGM in New Zealand, as recorded in the snowline lowering of mountain glaciers at Lake Pukaki, happened 18,000 + 2,000 years ago. This is in striking agreement with studies of "mountain glacier LGM" in mid-latitude South America [3] on one hand and in northern mid-latitudes, i.e. in Switzerland, on the other [4]. Note that not only the timing but also the absolute and relative extension of the Late Glacial advances in these three sites are very similar.

(II) The highstand of mountain glaciers during the LGM in New Zealand occurred some 10,000 years prior to the final collapse.

Fig. 1: Photograph of the Lake Pukaki area with the preliminary surface exposure ages. The age of the "Outermost Moraine" is based only on sample 421 so far; the age of the Lake Moraine is derived from samples 404, 406, and 408. Note the clearly defined terminal moraine set, from the "Outermost Moraine" to the "final" LGM lake moraine. [Ivy-Ochs et al., in prep.], dated the Birch Hill moraine marked in the background (see Ivy-Ochs et al., this Annual Report).

The preliminary bottom line of this work is that the termination of the "mountain glacier LGM" occurred synchronous in mid-latitudes of both hemispheres. This implies either a symmetric trigger area, i.e. the tropics, or, if the end of the LGM is triggered elsewhere, a rapid signal transfer, i.e. through atmospheric processes. Together with the work of [Ivy-Ochs et al., in prep], the Lake Pukaki area might become the reference area for mountain glacier dynamics during the late glacial period in southern mid-latitudes.

REFERENCES

[1] T. Blunier et al, Nature 394, 739 (1998).

[2] R. B. Alley and P. U. Clark, Ann. Rev. Earth Planet. Sei. 27, 149 (1999).

[3] G. H. Denton et al., Geografiska Annaler 81 A(2), 107 (1999).

[4] S. Ivy-Ochs, Ph. D. Thesis, ETH Zürich (1996).

174

RECONSTRUCTION AND SURFACE EXPOSURE DATING OF THE LAST ICE CAP IN THE WESTERN ALPS

MA. Kelly, C. Schlächter (Univ. Bern); P.W. Kubik (PSI)

A reconstruction of the last maximum ice cap in the western Alps provides the most accurate representation of the former ice surface and reflects the main precipitation sources that led to ice accumulation. Surface exposure dating used to determine the age of déglaciation from the last maximum ice surface shows that the Alpine ice cap existed during the Würm glaciation and suggests that the high elevation southern Valais was deglaciated by -13,000 yr B.P.

The surface configuration of the last maximum Alpine ice cap is reconstructed based on detailed mapping of glacial erosional features, which indicate the former ice surface elevation and flow directions within the western inner-Alpine region. The ice surface reconstruction for the western Alps, combined with previous work from the western and central Alps, provides the most accurate representation of the last maximum ice-cap surface in the Swiss Alps [1, 2].

Within the inner-Alpine region, the former ice cap was characterised by ice domes (areas of high ice accumulation from which ice flowed outward in all directions). The locations of three ice domes in the central Alps and the direction of ice flow over high Alpine passes indicate that the former ice cap was influenced by dominant southerly air circulation and precipitation [3]. The locations of two ice domes in the western Alps were strongly influenced by the high surface topography of this region. However, the ice dome over the Mt. Blanc massif had an asymmetrical surface (200-300 m higher on the southern side) suggesting an influence of southerly circulation on ice accumulation.

A major question exists as to the age of this last maximum ice cap in the inner-Alpine region. Surface exposure dating of mapped erosional features enables a minimum age of déglaciation from the maximum ice surface to be determined. The cosmogenic nuclide 1 0 Be was measured in steeply-dipping striated bedrock surfaces at two locations in the western Alps approximately 100-200 m below the former maximum ice surface (as marked by glacial trimlines). Preliminary surface exposure dates from near the Lac d'Emosson and in the Saastal are shown in Fig. 1.

The surface exposure dates indicate that high-elevation erosional features were formed by an ice cap that existed in the Alps during the Late Würm glacial stage. This maximum ice surface in the inner-Alpine region is consistent with the Würm maximum extent of glaciers on the northern Alpine foreland at <28,060 + 340 1 4 C yr B.P. [4].

The Saastal sampling site is located approximately at the midpoint in the length of the valley, at 2500 m elevation on the eastern side. The 1 0 Be dates from the Saastal site suggest that the valley glacier receded from the sample site by at least 13,000 yr B.P. Previous work, based on radiocarbon dates, suggested that déglaciation occurred simultaneously in the northern Alpine foreland and in the inner-Alpine pass regions at -14,000 1 4 C yr B.P. [5, and references therein]. The new surface exposure dates suggest that the high elevation southern Valais may have remained ice covered during the initial déglaciation of the northern Alpine foreland.

The Lac d'Emosson Be dates indicate déglaciation occurred by at least 10,000 yr B.P. Déglaciation at the Lac d'Emosson sample sites may have occurred at a later time than in the Saastal, because the Lac d'Emosson region is a high basin, between 2300 and 2500 m elevation above the main valley, and was most likely influenced by Late Glacial-age ice re-advances.

SA-2 S/W x

EM-4 /i St

/ / EM-5

T

I 1 ' X I /

\ y Saastal Lac d1 Emosson

sample

Fig. 1: Be surface exposure dates from glacially eroded bedrock surfaces near the Lac d'Emosson and in the Saastal. Duplicate samples are individually processed and measured.

The surface exposure dates indicate the general timing of déglaciation from the highest ice surface in the inner-Alpine region. Samples from Grimsel Pass will also be measured in order to provide more information about the déglaciation of high alpine passes.

REFERENCES

[1] H. Jäckli, Bundesamt f. Landestopogr., Blatt 6 (1970).

[2] D. Florineth and C. Schlüchter, Eclogae Geologicae Helevetiae 91, 391 (1998).

[3] D. Florineth and C. Schlüchter, Quat. Res. 54, 295 (2000).

[4] C. Schlüchter and C. Röthlisberger, Jubiläums-Sympo-sium d. Schweiz. Gletscherkommission, 47 (1993).

[5] C. Schlüchter, Bulletin de l'Association française pour l'étude du Quaternaire 2/3, 141 (1988).

175

PLEISTOCENE AND HOLOCENE GLACIER ADVANCES IN CENTRAL ASIA AND NEPAL AS ASSESSED BY IN SITU COSMOGENIC 1 0 Be EXPOSURE AGES OF

MORAINE BOULDERS

U. Abramowski, B. Glaser, W. Zech (Univ. Bayreuth); S. Ivy-Ochs (ETHZ); P.W. Kubik(PSI)

In situ cosmogenic 10Be concentrations in samples from lateral and frontal moraine boulders from the Turkestan Range and the Alay Range (Kyrgystan), and the Gorkha Himal (Nepal) yield exposure ages corresponding to glacier advances -3000, -11,000, -20,000, -60,000 and >60,000 y BP. Our results corroborate the hypothesis, that, at least in the Alay Range, the maximum glacier advance was during the late Pleistocene (OIS-4).

AMS measurements of in situ cosmogenic 1 0 Be in quartz from boulders exposed at the crest of moraines has proved to be an excellent means of constraining the ages of the glacier advances which have left these deposits [1]. In particular, it is a promising way to support and elaborate the theory of asynchronous maximum advances of mountain and continental glaciers during the late Pleistocene [2].

Samples were collected in 1998 in the Aksu Valley, Turke­stan Range, Kyrgystan (39.6°N, 70°E; Figure 1, left picture), in 1999 in the Koksu Valley, Alay Range, Kyrgystan (39,6°N, 72°E; Figure 1, left picture), and again in 1999 in the Macha Khola Valley, Gorkha Himal, Nepal (28,3°N, 84°E; Figure 1, right picture).

Fig. 1: Investigation areas in Central Asia.

1 0 Be was extracted from the quartz of a sample following the procedure set up by [3]. The 1 0 Be concentration was then measured at the AMS facility at PSI/ETHZ. The calculation of the exposure ages followed [4], modified by [5], under the assumptions of flat horizontal surface geometries for the samples and negligible erosion. Shielding factors were calculated for the Aksu Valley following [6] and using a map based on satellite images. Shielding was estimated to be similar for all other sites.

In the Aksu Valley, samples from three lateral moraine ridges supposed to be of LGM and Late Glacial ages, yielded 1 0 Be exposure ages of a) 20.6, 17.3, 17.2, 13.8, 11.2 ka, b) 24.3, 20.4, 19.9, 18.9, 15.4 ka, and c) 26.6, 21.7, 17.8, 13.4 and 10.1 ka. These results suggest that all three moraine ridges must be assigned to phases of the LGM, with a mean age of ~ 19-20 ka BP. However, the large scat­ter of the data does not allow to separate different phases. An older moraine consisting of single, highly weathered boulders from a more extensive glaciation was recognized in the valley, but could not be dated reliably.

In the Koksu Valley, 1 0 Be exposure ages of 11.4, 11.5 and 11.5 ka were obtained from a frontal moraine supposed to

be of Late Glacial to early Holocene age, clearly assigning this moraine to a global Younger Dryas advance, as previously documented by exposure ages elsewhere [7]. From the lowest frontal moraine of the valley, ages of 65.7, 60.1 and 56.1 ka were obtained, thus giving for the first time reliable evidence of an ice advance during oxygen isotope stage 4 (OIS-4) in Central Asia.

In the Macha Khola Valley, samples from a moraine supposed to be of Neoglacial age yielded exposure ages of 3.2, 3.2, 2.8 and 1.8 ka corroborating our field observations. Samples from a lateral moraine supposed to be of Late Glacial or Holocene age, 1 0 Be exposure ages of 11.7 and 11.1 ka, again imply the global Younger Dryas advance [7]. Samples from the frontal moraine of the most extensive glaciation recognizable in this valley yielded exposure ages of 160, 89, 57, 51, and 40 ka. Since these values are not erosion-corrected, and since inheritance cannot be excluded in the samples yielding the higher ages, it is not possible to unequivocally assign the deposit to an OIS-4 or to an OIS-2 glacier advance. Nonetheless, it remains possible, that here again the maximum advance of the ultimate glaciation has preceded the LGM.

We have been able to determine the 1 0 Be exposure ages of several moraines with a satisfying degree of precision, for other samples scatter has been unexpectedly high. Nevertheless, these results prove the existence of extensive glaciations in Central Asia during OIS 4 as well as OIS 2 [8].

REFERENCES

[1] J. Gosse and F. Phillips, Quat. Sei. Rev. 20, 1475 (2001).

[2] A. Gillespie and P. Molnar,

Rev. Geophysics 33, 311 (1995).

[3] S. Ivy-Ochs, Diss. ETH 11763, Zürich 1996.

[4] D. Lai, Earth Planet. Sei. Lett. 104, 424 (1991).

[5] J. Stone, J. Geophys. Res. 105 B 10, 23753 (2000).

[6] J. Dunne et al., Geomorphology 27, 3 (1999). [7] S. Ivy-Ochs et al., Geografiska Annaler 81 A, 313

(1999).

[8] J. Schäfer et al., Earth Planet. Sei. Lett. 194, 287 (2002).

176

RECONSTRUCTING PALEO-GLACIATIONS ON THE TIBETAN PLATEAU BY SURFACE EXPOSURE DATING

/. M. Schäfer (LDEO); S. Tschudi (Univ. Bern); Z. Zhao (CAGS, China); X. Wu (CAS, China); S.Ivy-Ochs, R.Wieler, H. Baur (ETHZ); P.W. Kubik (PSI); P. Schlosser (LDEO); P. Oberholzer (ETHZ);

C. Schlachter (Univ. Bern)

First surface exposure ages from moraines in Central and East Tibet exclude a significant influence of glaciations in Tibet on the Earth's climate system over the last 170 ka. A rather small glacial advance occurred in East Tibet during Marine Isotope Stage 2 (MIS-2) indicating a climate relation between Tibet and the "classical" Northern Hemisphere.

Extensive ice cover on the Tibetan Plateau would significantly influence the Earth's climate in general and the Asian monsoon system in particular. However, extent and timing of Quaternary glaciations in Tibet remain still highly controversial. E.g., it is still unclear, if the drastic albedo increase of Eurasia related to a potential ice-dome covering substantial parts of the Tibetan Plateau in the past triggered hemisphere-wide to global climate changes. Since 1997, we investigate the lowering of palaeo-snowlines of Tibetan glaciers to learn more about the climatic interconnection between the Tibetan Plateau and the rest of the planet. Is the Tibetan Plateau climatically driven by the surrounding monsoon systems of India and East Asia as suggested by e.g. [1]? Is it related to the "classic" North Atlantic climate recorded in the Greenland ice cores? Or is the climate in Tibet dominated by local triggers?

- ¿ •„ jù H ü h l - -. , ^ 1

Fig. 1: Map of the Tibetan Plateau showing the sampling sites of the 1997/98 expeditions (() (results presented in [2]), and the sites of the 2001 expedition (I ). The dashed and the dotted arrows indicate the potential connection to the North Atlantic climate and the influence of the monsoon, respectively. The dotted ellipse roughly sketches the source area of a hypothetical ice dome covering substantial parts of the Plateau (see text).

To tackle these problems we date erratics on top of moraines to reconstruct the glacial advances and the underlying climate excursions. We apply the method of Surface Exposure Dating of erratics with cosmogenic 1 0 Be, 2 6 Al, and 2 1 Ne. In 1997 and 1998, we concentrated on the

climatic key areas of Central (Tanggula) and East Tibet (Litang). The results were published in [2]. In 2001, we went to South Tibet, Nyalam County, on the northern flank of the Himalayas (Fig. 1).

Cosmogenic nuclide data imply that the most extensive glacial advance in the Tanggula area, which was still rather small (some 25 km from the glacial cirque), occurred more than 170 ka BP ago. Since then, no more extensive glacial advances occurred. Therefore, this data set excludes a climate-influencing ice dome on the Tibetan Plateau since 170 ka ago. Glaciations have been minor in central Tibet during the last two glacial cycles, most likely due to constant arid conditions.

In the Litang area, a glaciation during MIS-2 is identified. This implies a climate coupling to the "classical" Northern Hemisphere rather than a dominant influence of the monsoon system in Tibet. This finding from East Tibet is inconsistent with reports from asynchronous glacial advances in Southwest Tibet (e.g. [1]). These authors argue that during periods of Northern Hemisphere inter-stadials, the high insolation intensifies the Indian monsoon, which increases summer precipitation in the West Himalayas triggering glacial advances.

The data set to be produced from the 2001 campaign to the Nyalam County, central part of the Himalayas, can be expected to shed light on this conflict. Besides its well preserved moraine record, the Nyalam area is of special interest, as a "gap" in the Himalaya chain opens the pathway for the Indian monsoon, which creates a very humid environment. As a monsoon hot-spot within the Himalayas, Nyalam mountain glaciers are especially appropriate to evaluate the importance of the Indian monsoon system for the timing of climate changes in Tibet. In addition, due to higher precipitation, this glacial system is expected to record even rather short and abrupt climate changes.

REFERENCES

[1] L. A. Owen, et al., J. Quat. Sei. 16 (6), 555 (2001).

[2] J. M. Schäfer et al., Earth Planet. Sei. Lett. 194 (3-4), 287 (2002).

177

EROSION STUDIES OVER VARIOUS SPATIAL AND TEMPORAL SCALES USING IN SITU-PRODUCED COSMOGENIC NUCLIDES IN SEDIMENTS

F. von Blanckenburg (Univ. Bern; now Univ. Hannover); M. Schaller, T. Hewawasam, P. Morel (Univ. Bern); P.W. Kubik (PSI)

We report on four years of research into quantification of spatially averaged erosion rates using cosmogenic nuclides in river sediments. Applications range from the characterization of geomorphic change in the European landscape to erosion studies in tropical islands affected by deforestation, and the determination of "paleo erosion rates" on buried sediments.

Since 1998, the Berne Isotope Geology group and the Laboratory for Ion Beam Physics of PSI and ETHZ in Zurich have undertaken a major effort to explore applications of erosion studies using in «Yw-produced cosmogenic 1 0 Be and 2 6 Al. The basic principle is that a catchment-wide erosion mass balance is calculated from the cosmogenic nuclide abundance of quartz in river sediments. At steady state, the flux of nuclides out of the catchment (by erosion followed by river sediment transport) equals that into the catchment (by the known altitude- and latitude-scaled production rates of cosmogenic nuclides). An erosion rate integrating over the entire catchment can be calculated. The time scale explored is given by the mean cosmic ray attenuation pathlength (ca. 60 cm) divided by the erosion rate. In our Middle European catchments, this time scale is between 10 and 30 ka. In some of our Sri Lankan catchments, this time scale is between 30 and 150 ka. To date, the principle results are as follows.

1) Erosion rates in Middle European uplands range from 10 to 50 mm/ka. In uplands of crystalline bedrock, erosion rates are strongly topography-dependent. In fact, the technique allows, for the first time, to explore the detailed relationships between relief and erosion. In sedimentary bedrock, a distinct dependency of bedrock composition can be quantified. (Mirjam Schaller, Ph.D. thesis, also [1])

2) River terraces are sediments that bury the erosion products of past periods. If the age of the terrace is known, then samples taken from a depth in which post-depositional shielding is negligible yield "paleo-erosion rates". The cosmogenic technique is the only approach capable to provide such data. Terraces have been sampled in great detail through the last climate cycle. Erosion rates in Allier (Massiv Central, France) and Meuse (Ardennes, The Netherlands) terraces have been higher in the last cold period (e.g. 30 ka to 10 ka) than today. This is explained by the lower vegetation level and by periglacial (partial frozen soil) erosion processes at that time. Given the long integration time of the method, the signal of these elevated rates is carried as a "memory" into recent river sediments, although erosion has decreased. (Mirjam Schaller, Ph.D. thesis)

3) The same approach was applied to a 1.6 Ma terrace record in the Meuse catchment. Surprisingly constant

erosion rates of ca. 25 mm/ka from 1.5 to 0.4 Ma result, despite significant global cooling during that period. At 0.4 Ma, increased uplift of the Ardennes mountain chain lead to elevated erosion rates. (Mirjam Schaller, Ph.D. thesis)

4) Cover beds, widespread on hillslopes of temperate climate zones, represent layers of allochtonous material laterally transported by periglacial processes in the last cold periods. In s/ta-produced 1 0 Be was analyzed in quartz from soil sections from Middle European landscapes affected by cover bed formation. Depth profiles give discontinuous zigzag-like patterns. This is in Une with deposition of allochtoneous material. Modeling the ages of irradiation between soil movements is compatible with transport events during the Last Glacial Maximum and the Younger Dryas, respectively. (Mirjam Schaller, Ph.D. thesis)

5) The effects of river capture and gorge formation was explored in the Wutach catchment (southeastern Black Forest, Germany). 18 ka ago, the river Wutach changed course from being a Danube tributary to draining into the river Rhine. A deep gorge formed. Although this event is violating the cosmogenic steady-state assumption, cosmogenic nuclides still yield robust catchment-wide erosion rates. This is because the area incised is small compared to the entire catchment. However, sediments affected by the glaciation of the high Black Forest yield perturbed results. (Philippe Morel, Diploma thesis).

6) Sri Lanka is a tropical island featuring a 2500 m altitude mountain range. Contrary to all expectations, erosion rates in the center of this mountain range are as low as 3 mm/ka. We explain this by the presumably ancient topography of the island, absence of tectonic movements, protection of bedrock by highly weathered soils, and protection of soils by rain forest. Where this forest has been cleared for agriculture, recent soil erosion rates have increased up to 100 times. (Tilak Hewawasam, ongoing Ph.D. project).

REFERENCES

[1] M. Schaller et al., Earth Planet. Sei. Lett. 188, 441 (2001).

178

PALEO-EROSION RATE RECORDS FROM COSMOGENIC l u B e IN A 1.6 MA TERRACE SEQUENCE OF THE MEUSE RIVER, THE NETHERLANDS

M. Schaller (Univ. Bern); F. von Blanckenburg (Univ. Bern; now Univ. Hannover); A. Veldkamp, M. W. van den Berg (Wageningen Univ.); N. Hovius (Cambridge Univ.); P.W. Kubik (PSI)

Terrace deposits of known age provide suitable records of "paleo-erosion rates". These can be determined by in situ-produced cosmogenic 10Be in quartz. Here we present a 1.6 million-year erosion rate reconstruction of the Ardennes mountain range.

The method to study paleo-erosion rates utilises the fact that river-borne quartz carries a cosmogenic nuclide memory that is a function of the spatially averaged catchment erosion rate [1]. If incorporated into a river terrace, the hinterland's erosion rate at the time of deposition can be measured today.

For this technique, an important requirement is that the river terrace sediments sampled have been buried deeply, such that post-depositional exposure is negligible or that post-depositional exposure can be corrected by using the independently known age of the terrace and the sampling depths. Both parameters, however, introduce considerable sources of error.

Erosion rates of the Meuse River in The Netherlands (Fig. 1), mainly reflecting cold-stage erosion of the Ardennes mountains, are surprisingly uniform with 16 to 26 mm/ka from 1.6 to 0.4 Ma ago (Fig. 2). Neither the global Pleistocene cooling nor the Middle Pleistocene transition away from dominant 41 ka cycles at ~ 1.2 Ma appears to have an effect on erosion.

Meus©/_)

&\ \

* \ France {y

s * \

*( /Venlo

0 / R o e r m o n d

* / y &

* m%i

Heerlen I m \

I Maastricht \

In contrast, tectonic change doubles erosion to 35 mm/ka to 40 mm/ka after 0.4 Ma (Fig. 2). Interestingly, this time is ca. 0.3 Ma after an increase in river incision rate caused by accelerated uplift of the Ardennes Mountains. It points to a substantial lag time required for linear incision to propagate into spatial erosion of an entire river basin as reflected by cosmogenic nuclides.

80-

60-

_ 40

20

m Pleistocene Meuse terraces « Late Pleistocene to Holocene terraces a Modern river bedload

Incision rate (van Baien et al., 2000)

0.0 5,0x105 1.0x10* 1.5x10s

Time before present (a)

Fig. 1: Map of the Meuse Catchment with terrace sampling locations (stars)

Fig. 2: Paleo-erosion rates calculated from cosmogenic 1 0 Be concentrations in river-borne quartz of Meuse terraces (squares). The variance over time in the calculated erosion rates is small. Cosmogenic nuclide-derived erosion rates from Late Pleistocene to Holocene (circles) and modern river-bedload (triangles) are also shown for comparison. The solid line shows the uplift rate of the Ardennes Mountains. Note that an increase in catchment-wide erosion rate is 0.3 Ma after the rise of the Ardennes.

It is interesting to note that the scatter in erosion rates is largest in a Late Pleistocene and Holocene terrace sequence studied in more detail (round data points in Figure 2). The probable reason is that this late sequence includes Holocene warm-period sediments that stem from an entirely different erosion regime than the earlier Pleistocene terraces. The latter have been deposited in cold periods only.

REFERENCE

[1] M. Schaller et al., Earth Planet. Sei. Lett. 188, 441 (2001).

179

QUANTIFICATION OF THE EFFECTS OF LITHOLOGY, LANDSCAPE DISSECTION, AND GLACIATION ON ROCK WEATHERING AND LARGE-SCALE EROSION AS

DETERMINED BY COSMOGENIC NUCLIDES IN RIVER SEDIMENTS

P. Morel (Univ. Bern); F. von Blanckenburg (Univ. Bern; now Univ. Hannover); M. Schüller (Univ. Bern); M. Hinderer (TUDarmstadt); P.W. Kubik (PSI)

The effects of river capture and gorge formation on the determination of catchment-averaging erosion rates by cosmogenic nuclides was explored in the Wutach catchment (southeastern Black Forest, Germany). Although the capture is violating the steady-state assumption, cosmogenic nuclides still yield robust erosion rates. However, sediments affected by the glaciation of the high Black Forest yield perturbed results.

Cosmogenic nuclides measured in quartz in the bedload of rivers present a novel tool to quantify surficial processes at the 10 4 a time scale.

Here we present an investigation of the effects of lithology, river incision, and Last Glacial Maximum (LGM) glaciation on erosion rates in the medium-scale (346 km 2) upland catchment of the river Wutach (Black Forest, Germany). The erosion rates measured with 1 0 Be are strongly controlled by lithology: sandstone lithologies erode at 9-14 mm/ka, granite lithologies at 27-37 mm/ka, and limestone lithologies (as deduced from river load gauging) at 70-90 mm/ka (Fig. 1).

100

m T ® m « LD T - <n o CM -C

o o ^ o o 5 t < 5 r i ; ra

a a s S a a S g S S g g - g O

Sample

O Sandstone catchement (cosmogenic)

O Granite catchement (cosmogenic)

B Limestone catchement (total load)

Dependency of erosion rate on bedrock lithology. Granite and sandstone lithology erosion rates have been determined by cosmogenic nuclides, whereas those from limestone are from gauging of the dissolved load of the respective tributaries.

From 18 ka BP, the Wutach basin was strongly affected by capture-induced incision. At that time, the Wutach changed from being a tributary to the river Danube to being a tributary to the river Rhine. The base level was lowered by about 100 m. A deep gorge formed (Fig. 2).

Fig. 1:

Since the cosmogenic time scale of these measurements means that we are integrating over only ca. 20 ka, the instantaneous incision represents a violation of the steady-state assumption the method is based on. We have tested the effect of this violation by comparing incised streams with non-incised streams of the same lithology in the adjacent Danube catchment. Surprisingly, we see no difference in catchment-wide erosion rates between both catchments.

Fig. 2: 18 ka ago, the Wutach landscape was dissected by river incision. Today, erosion rates from cosmogenic nuclides in river sand are dominated by the non-incised landscape surrounding the gorge.

Based on mass balance considerations, we can demonstrate that in the Wutach case the effect of the capture-induced incision is negligible on the cosmogenic nuclide budget when compared to all other uncertainties that are involved in these calculations. We infer that the time required for the entire catchment to be affected by landscape change resulting from the incision is much longer than 18 ka. Schaller et al. [1] report on a time scale of 300 ka for tectonic change to translate into changes in catchment-wide erosion rates.

We have also tested the effect of glaciation of the higher elevations of the Black Forest during the LGM. Those parts of the catchment, which had been affected, had a clearly noticeable effect on the cosmogenic budget resulting in nuclide concentrations lower by up to 20%.

REFERENCE

[1] Schaller et al., PSI Scientific Report 2001,1.

180

4 1 C a INTERCOMPARISON MEASUREMENTS

C. Schnabel (ETHZ); H.-A. Synal (PSI); C. Geppert, K. Wendt (Univ. Mainz); L. K. Fifield (ANU)

The results of intercomparison measurements of standard materials and samples using AMS (at ETH/PSI and at the Australian National University (ANU)) and RIMS (at the University of Mainz) are shown. 41Ca/°Ca ratios from absolute measurements in Mainz and ANU are within the one sigma uncertainty of the standard material used.

At the PSI/ETH AMS facility, 4 1 Ca/ 4 0 Ca measurements are routinely made using CaH 2 as target material. Isobaric interference from 4 1 K ions can be suppressed sufficiently to reach detection limits of less than 10"13. At present, our primary applications are related to the investigation of 4 1 Ca production in meteoroids and to the OSTEODIET [1] project within the European 5 t h Framework program on Nutrition and Health.

Our 4 1 Ca measurements are carried out relative to material diluted from a standard whose 4 1 Ca concentration was determined by liquid scintillation counting at PTB, Braunschweig [2]. The nominal 4 1 Ca/ 4 0 Ca ratio of the material we use as our primary standard (JUEL) is (1.04 ± 0.08)-10"9. In addition, we use secondary standards (e.g. VILL04) calibrated against JUEL. To validate the quality of our 4 1 Ca measurement procedure, we and the AMS group of ANU performed intercomparison measurements of these standard materials and of one meteorite sample.

A metal separate from meteorite Estherville (piece No. N1025C) was the comparison sample. Ca(OH)2 was prepared after addition of Ca carrier of terrestrial isotopic composition and then divided into two parts. One aliquot was further prepared as CaH 2 for the measurement in Zurich, whereas CaF 2 was prepared from the other aliquot for ANU. The results (as activity concentrations in dpm/kg metal) were 16.52 ± 2.24 for the Zurich and 16.82 ± 1 . 1 9 for the ANU sample. The isotopic ratios measured at PSI7ETH normalized to the respective ANU results are summarized in Table 2. All results agree with the nominal value of our primary standard and its one sigma error of about 7.6%. On the other hand, all absolute measurements at ANU gave higher isotopic ratios than the relative measurements at ETH/PSI.

Table 2: Isotopic ratios 4 1 Ca/ 4 0 Ca (x) obtained at ANU divided by the isotopic ratios measured at ETH/PSI.

Sample (x) ANU / (x) ETH/PSI JUEL 1.058 ±0.030 VILL04 1.059 ±0.038 Estherville N1025C metal 1.018 ±0.156

According to the objectives of the OSTEODIET project, 4 1 Ca/ 4 0 Ca isotopic ratio measurements of blood and urine samples from 4 1 Ca labelled women will be carried out in Zurich by AMS as well as in Mainz by Resonant Laser Ionization Mass Spectrometry (RIMS). To check for comparability of both methods, a second intercomparison experiment with three samples from proton irradiation experiments has been performed. The results are shown and discussed in detail elsewhere [3]. The 4 1 Ca/ 4 0 Ca ratios determined by RIMS, normalized to the respective AMS results from ETH/PSI, are shown in Table 3 together with the isotopic ratios measured by AMS. Note that the

Measurements at ANU are carried out as absolute measurements, i.e. without using a standard material for calibration. However, fractionation effects during negative ion formation, the stripping process and beam transport could affect the measured isotopic ratios. The 4 1 Ca/ 4 0 Ca ratios measured for the two standard materials and for the meteorite sample are shown in Table 1. Note that "JUEL" was used for normalization in Zurich. The nominal value is therefore given in Italics instead of a measured result.

Table 1: 4 1 Ca/ 4 0 Ca ratios measured at ETH/PSI and at ANU, Canberra.

Standard ETH/PSI ANU JUEL 1.04*10-" (1.10 ± 0 . 0 1 ) * 10 - 9

VILL04 (2.44 ±0.01)* 10"11 (2.59 ± 0.09) * 10"u

Esthl025C (2.11 ±0.28) * 10"12 (2.14 ± 0 . 1 5 ) * 10"12

absolute measurements of RIMS were higher for all three samples.

Table 3 : Comparison of measured 4 1 Ca/ 4 0 Ca ratios by RIMS and AMS

Sample (RIMS) / (AMS) 4 1 Ca/ 4 0 Ca (AMS) FESC005 1.027 ±0.094 (2.13 ±0.09) *10"1U

FESD004 1.044 ±0.154 (1.84 ±0.08) * 10"1(J

FESF011 1.236 ±0.363 (3.64 ±0.19) n O " 1 1

The uncertainties of the normalized ratios result mainly from the one sigma errors of the RIMS measurements, which amounted to 8.2% and 14.1% respectively for the two samples with isotopic ratios of about 2 * 10"10.

A C K O W L E D G M E N T

We are grateful to R. Michel and U. Herpers for the irradiations with protons, to S. Merchel for a part of the sample preparation of these samples, and to G.F. Herzog for making available the meteorite sample.

REFERENCES

[ 1 ] 5 t h Framework programme of the European Union, Contract No.: QLK1-199-00752

[2] B. Dittrich-Hannen et al., Nucl. Instr. Meth. B 113, 453 (1996).

[3] K. Wendt et al., Nucl. Instrum. Meth., in preparation.

181

1 Z V I AND 1 Z / I IN EUROPEAN SOILS

T. Ernst (Univ. Hannover); S. Szidat (Univ. Hannover, Univ. Bern, PSI); J. Handl, D. Jakob, R. Michel (Univ. Hannover); C. Schnabel (ETHZ); H.-A. Synal (PSI); F. J. Santos Arevalo (Univ. Sevilla); I. Benne, J.Boess, E. Gehrt, A.Capelle, J.Schneider, W. Schäfer (NLfB Hannover)

129 129 127

In order to quantify the anthropogenic I input into soils, I and I were analyzed by AMS and ion chromatography, respectively, in 7 soils from Lower Saxony (Germany) up to a depth of 250 cm. Considering the

129 127 129

different time periods for the input of I and I, it was possible to use anthropogenic I as a tracer for the explanation of the iodine migration process in soils [1 ].

In the last 50 years, the environmental abundance of I has been increased by several orders of magnitude as a result of the use of nuclear fission and, in particular, as a result of emissions from nuclear fuel reprocessing plants. We therefore started investigations into the 1 2 9 I budget to quantify the anthropogenic changes and the behavior with time [2].

Based on systematic examinations of 1 2 9 I in rain, surface-and groundwaters in Lower Saxony, in soil profiles from the Ukraine and in pre-nuclear soils from Russia, we could describe the 1 2 9 I input into Lower Saxony soils by means of 1 o n 1 0 1 1OQ

1/ I isotope ratios [3-4]. An anthropogenic input of I was observed in all seven Lower Saxony soils down to the

1 o n 1on

deepest sample depths. The observed 1/ I isotopic ratios are between (5.2 + 0.3) • 10"8 at the surface and (5.4 + 0.6) • 10"11 below. These ratios - even at a depth of 250 cm- were higher by one order of magnitude compared to the lowest measured ratio of (5.7 + 1.1) • 10"1 2in pre-nuclear soils [4]. In comparison to Chernobyl accident unaffected Ukrainian soils we have found 1 2 9 I contaminations in Lower Saxony higher by factors of three to four in terms of integral average deposition densities. Table 1: Integral deposition densities of I and I.

Land utilisation / location 1 2 9 I / mBq/m 2 1 2 7 I / g / m 2

Pasture / Vestrup 390 + 50 2.3 + 0.5 Forest / Eilenriede 178 + 26 2.4 + 0.4 Lawn / Ricklingen 118 + 25 2.5 + 0.4 Farmland / Twenge 158 + 20 3 .1+0.5 Farmland / Barum 1 3 6 + 1 6 3.5 + 0.4 Farmland / Adenstedt 1 2 4 + 1 6 6.4+ 1.1 Farmland / Groß Lobke 1 7 1 + 2 3 7.2 + 0.9 Geometric mean 168 • 1,1" 3.5 •

1.2"

Chernobyl accident unaffected Ukrainian soils [5]

38 • 1.7"

Russian soil / 1939 [4] 0.084 + 0.017

We observe different exponential depth dependences of the 1 o n i on

I and I concentrations in topsoils and in subsoils. Based on 1 2 7 I contents, the sequence of some of the soils correlates inversely with 1 2 9 I contents for any depth (Fig. 1). Within our model, this is interpreted as an accelerated migration of modern iodine correlated with decreasing 1 2 7 I contents in the subsoil. We conclude that an interchange

1 on i o n

between immobilised I with free I allows an

immobilisation of I in soils. Furthermore, we postulate equilibrium conditions of this interchange in different adsorption sites (physical or chemical sorption) and in different soil properties. We infer that 1 2 9 I can only be immobilized as a result of dynamic equilibrium, which interchanges iodine in the timeframe of the enhanced 1 2 9 I input. This is the case for physical sorption and sorption on organic matter. In combination with soil properties and flow properties of water in the soil we can interpret all iodine distributions in the soils. The model explains the fact that iodine has mostly accumulated in the topsoil due to high availability. It also explains, based on the special soil properties, even the highest 1 2 9 I integral deposition density with the least significant 1 2 7 I deposition density (pasture Vestrup). Furthermore, we conclude that 1 2 9 I from the anthropogenic input has passed through the soi ls and reached the groundwater. Consequently, integral deposition densities are lower limits of the anthropogenic 1 2 9 I input.

depth of projections surface / cm -0-forest Eilenriede -A-pasture Vestrup -©-lawn Ricklingen

- o - acre Groß Lobke -o -acre Adenstedt - d - a c r e Twenge

—ti- acre Barum

Fig. 1: Surface-projected 1 2 7 I (lower part) and 1 2 9 I (upper part) contents in Lower Saxony soils.

REFERENCES

[1] T. Ernst et al., Proc. 34. Jahrestagung des Fachver­bandes für Strahlenschutz, (2002) in press.

[2] A. Schmidt et al., Sei. Total Environ. 223, 131(1998). [3] S. Szidat et al.,

Nucl. Instrum. Meth. B172, 699 (2000). [4] S. Szidat, Ph.D. Thesis, Univ. Hannover (2000). [5] R. Michel et al., Berichte der Strahlenschutz-

kommission, (2002) in press.

182

DETERMINATION OF l u Be AND MAl IN METEORITE ACFER 168 AND A MODEL CALCULATION TO RECONSTRUCT ITS SIZE AS A METEOROID.

A. Tarabischi, T. Bastian, U. Herpers (Univ. Köln); R. Michel (Univ. Hannover); P.W. Kubik (PSI)

Long-lived cosmogenic radionuclides (10Be, 26Al) were determined in stony meteorites by means of AMS after radiochemical separation. Using meteorite Acfer 168 as an example, we demonstrate that cosmogenic nuclide analysis and model calculations give information on the geometry of a meteorvid.

Long-lived radionuclides produced by cosmic ray exposure of meteoroids yield information which can be used to determine, on one hand, the spectral distribution and the constancy of the cosmic ray flux in the solar system and, on the other hand, to study the meteorite exposure history. In addition, it is possible to gain information about the size of a meteoroid.

Cosmogenic 1 0 Be and 2 6 Al concentrations have been determined in a large number of stony meteorites e.g. from the Sahara. The radiochemical separation of the radionuclides in the meteorites under investigation was based on the method of Vogt and Herpers [1].

Information on the exposure history of the meteorite can be obtained by comparing experimental results with model calculations (such as described in reference [2]). The model calculations describe the relations between exposure time, chemical composition, mass and shape of the meteoroid, and the depth of the sample in the meteoroid.

The calculated 1 0 Be and 2 6 Al activities can then be plotted as a function of the ratio of the radius of a meteoroid to the depth of the sample in a meteoroid (d/r). This, together with a known exposure age and measured 1 0 Be and 2 6 Al activities, makes it possible to reconstruct the size of the meteoroid and the location of the sample in it.

Q . TD

CD CÛ

Fig. 1: Calculated 1 0 Be activity vs. the ratio d/r for Acfer 168 for different meteoroid radii. d: depth of the sample below the surface of the meteoroid. r: radius of the meteoroid.

In the case of the meteorite Acfer 168, for example, an irradiation age of 5.5 Ma can be deduced from noble gas data [3]. Figures 1 and 2 show the relationships between the calculated 1 0 Be and 2 6 Al activities and the ratio d/r as functions of meteoroid radii ranging from 15, 25 and 32 to 40 cm.

75-. 70-65-

S 60-

[dpm

/ 55-50-

< CJ

45-40-35-

' i ' i • i • i ' i • i

L__^A »15 crrK S^C^"* -»25 cm; ^ 32 cm

40 cm ;

0,0 0,2 0,4 0,6 0,8 1,0 d/r

1,2

Fig. 2: Calculated 2 6Al activity vs. the ratio d/r for Acfer 168 for different meteoroid radii.

The activities of 1 0 Be and 2 6 Al were determined at the PSI7ETHZ AMS facility to 18.9 dpm/kg and 51.4 dpm/kg, respectively. With these activities, one can conclude that the analyzed sample of Acfer 168 should have been located no more than 14 cm below the surface of a meteoroid with a radius between 32 cm and 36 cm.

ACKNOWLEDGEMENT

Meteorites were kindly placed at our disposal by the Institut für Planetologie, Münster (Germany). The study was supported by the DFG and the Swiss National Science Foundation.

REFERENCES

[1] S. Vogt and U. Herpers, Fresenius Z. Anal. Chem. 331, 186 (1988).

R. Michel et al., Nucl. Instrum. Meth. 113, 434 (1996).

[2]

[3] L. Schultz, priv. comm.

183

INVESTIGATION OF PLATINUM GROUP ELEMENTS AT THE CRETACEOUS-TERTIARY BOUNDARY WITH ACCELERATOR SIMS

C. Maden (ETHZ); M. Döbeli (PSI); B. Hofmann (Nat. Hist. Museum, Bern)

Platinum Group Elements (PGE) have been examined with Accelerator SIMS at the PSI/ETH AMS facility in order to investigate the potential of the method for solving problems in geology or other fields of research. As an example the in-situ measurement of PGE in sedimentary layers of the Cretaceous-Tertiary (KT-) boundary are presented.

Platinum Group Elements are important trace elements especially in the field of geology and can be used to investigate major global events such as meteorite impacts. These events are manifested by anomalies in PGE concentrations in sedimentary layers. The excellent detection limits for trace elements in silicon together with a high lateral resolution of 100 um of the PSI/ETH Accelerator SIMS facility [1, 2] suggest that profiles of PGE concentrations in sedimentary layers can be measured in-situ with unequalled resolution and sensitivity. In order to demonstrate the potential of Accelerator SIMS, test measurements have been performed on samples provided by the Natural History Museum in Berne. Figure 1 shows a picture of the samples. They represent a continuous cross section through the sediment layers at the KT-boundary containing the PGE concentration anomalies produced by the meteoritic impact that occurred 65 million years ago. The Tertiary sediments are on the left and the Cretaceous layer on the right hand side of the picture.

The sedimentary layers were coated with a 50-nm thick carbon layer so that charging of the electrically insulating sample due to bombardment with the primary ion beam is avoided. An analysis of PGE was then performed with Accelerator SIMS at various points on the sample. In addition, the distributions of the main matrix elements were determined with RBS in a linear scan across the sample. The position of the scan on the samples is shown with the dashed white line in Figure 1.

Figure 2 shows a preliminary summary of the ongoing measurements. It can be seen that the counting rate of iridium measured with Accelerator SIMS shows a sharp increase in the Tertiary sediments when approaching the KT-boundary. The shape of the data matches extremely well previous Ir-concentration measurements performed with Neutron Activation Analysis [3]. Accelerator SIMS loses in sensitivity, however, when measuring in the sedimentary layers of the KT-boundary and the kaolinite clay. The reason can be seen in the change of the matrix components in these layers with respect to the Tertiary layer. The strong increase in the concentration of oxygen reflects a strong increase in the concentration of S I 0 2 and A1 2 0 3 in these layers. Since measurements of the sputter yield of negative ions from a S I 0 2 matrix [4] show that the detection limit of PGE are about two orders of magnitude worse than in a pure silicon matrix, it seems that the iridium concentration is below the detection limit of Accelerator SIMS in the layers with a high oxygen concentration. These detection limits are in units of atoms per matrix atom: 210" 9

for Pt, MO"7 for Ir, 210" 7 for Pd, 310" 7 for Au, 210" 8 for Os, 1 • 10"8 for Rh and 1 • 10"8 for Ag.

Fig. 1: Picture of the analysed sedimentary layers of the KT-boundary. The dashed line illustrates the position of the Accelerator SIMS and RBS measurements.

0 5 10 15 20 25 Position [mm]

Fig. 1: Abundance of some elements as a function of position across the sediments of the KT-boundary

Future measurements intend to reduce the lateral resolution of the concentration profile of iridium down to the 100 urn the apparatus is capable of resolving. Similar profiles of other PGE can be measured as well.

REFERENCES

[1] R. M. Ender et al.,

Nucl. Instrum. Meth. B123, 575 (1997).

[2] C. Maden, Diploma Thesis, ETH Zürich ( 1998).

[3] L. Alvarez et al., Science 208, 1095 (1980). [4] C. Maden, M. Döbeli, B. Hofmann,

PSI Sei. Rep. 1999,1, p. 199.

184

SELECTIVE ELECTRODEPOSITION OF Cu NANOSTRUCTURES ON FIB SENSITIZED p-Si

A. Spiegel (EPFL); R. Mühle (ETHZ, PSI); M. Döbeli (PSI); P. Schmuki (Univ. Erlangen-Nuremberg)

Ion beam induced surface damage on semiconductors may promote local electrochemical reactions, which can be used to deposit material selectively at the damaged sites. Based on previous work we have studied the relevant parameters in greater detail while increasing process resolution to less than 200nm.

It has been shown before that Focused Ion Beam (FIB) induced damage on p-Si can be used to trigger selective electrochemical reactions [1]. Our research has shown that at semiconductor defect sites the local Schottky barrier breakdown potential is significantly altered when compared to the intact surface. This difference can be used to trigger selective electrochemical reactions at the defect sites. Hence, maskless metal deposition in the sub-micrometer range becomes possible and may offer new methods for nanostructuring semiconductors [2].

For ion implantation we used the FIB system installed in the cleanroom of the Laboratory for Micro- and Nanotechnology (LMN) at PSI. We have been working with a Ga ion source built in-house. Ions were implanted with an energy of 30 keV and fluences were varied over 4 orders of magnitude (10 1 2 - 10 1 6 ions/cm2). The influence of fluence on electrochemical behavior was investigated. All electro­chemical experiments were carried out using a standard three-electrode setup (sample as working electrode, Pt counter electrode, standard calomel reference electrode -SCE) under potentiostatic or -dynamic conditions. Different electrolytes were used (0.01 M CuS0 4 + 0.05 M H 2 S 0 4 (+ 0.1 mM benzotriazole (BTA)) for Cu deposition under varying electrochemical conditions (time, potential, scanning speed).

Using microcapillary measurements [3] we were able to show the influence of electrochemical parameters (electrolyte, potential) and of the implant dose on deposition behavior.

io-6

io-7

10-»

10-9

10-10

10-"

1 0 - 1 2

10-«

- Unimp) anted Si " Implant 4, -1-1014ions/cm ;

- Implant 3, ~3-10,4ions/cnT - Implant 2, ~1-1015ions/crri ' Implant 1, ~3-1015ions/cm:

-2000 -1500 -1000 Potential / mV (SCE)

-500

The addition of BTA to the electrolyte lead to a significantly decreased Cu crystallite size. It is generally assumed that BTA adsorbs to the sample surface and hereby inhibits crystallite growth by hmiting surface diffusion of adsorbed ionic species (in this case, Cu + + ions).

Fig. 1: Current-voltage behavior of FIB sensitized p-Si (BTA containing electrolyte).

Fig. 2: Cu Une on p-Si sensitized by FIB (marker is 200 nm).

Fig. 2 shows a Cu Une deposited on p-Si implanted with ~ 1 1 0 1 5 ions/cm 2 (20s at -1500mV, with electrolyte as described above). The electrochemical process visibly reaches the resolution given by the FIB and structures in the sub-micrometer range are easily obtainable. No distinguishable grains or crystallites can be seen in Fig. 2 indicating that even smaller structures are possible. Selectivity is excellent and coverage of the implant site is complete.

In the near future we will focus our attention on further optimization of the deposition procedure and we are confident to reach the sub 100 nm resolution soon. Also, more fundamental aspects of the electrochemical behavior will be investigated.

REFERENCES

[1] A. Spiegel et al.,

J. Electrochem. Soc. 147, 2993 (2000).

[2] P. Schmuki et al., Phys. Rev. Let. 80,4060 (1998).

[3] H. Böhni et al., Surf. Coat. Techn. 130, 80 (2000).

185

RADIATION HARDNESS OF CdTe/CdS SOLAR CELLS UNDER LOW ENERGY PROTON IRRADIATION

D. L. Bätzner, A. Romeo, H Zogg, A. N. Tiwari (ETHZ); M. Döbeli (PSI)

The performance stability of CdTe/CdS thin film solar cells against radiation damage caused by protons has been investigated. A minor degradation is measured at high fluences for low energy protons of 650 keV. CdTe/CdS solar cells are highly suitable for space application.

The main power sources of most satellites are solar cells. Usually the solar power generators consist of high efficiency Si and III-V cells made of mono-crystalline materials. Not only the initial efficiency but also the stability against particle irradiation in space is an important factor for the long-term suitability of solar cells in space. In a preliminary study [1] the excellent stability of CdTe/CdS solar cells against high-energy protons was shown. In this work the stability of CdTe/CdS solar cells irradiated with low energy protons is described.

The CdTe/CdS solar cells were developed using a vacuum evaporation process on soda-lime glass yielding cell efficiencies in the range of 10 -12.5 % [2]. The most important parameter for the damage in solar cells is the non­ionizing energy loss (NIEL). The NIEL increases with decreasing proton energy. In a geostationary orbit a fluence of 5 1 0 1 2 cm"2 per year has to be expected for 1 MeV protons. Therefore, our investigation is focused on low energy protons of 650 keV, 1 MeV and 2.2 MeV with fluences ranging from 10 1 1 cm"2 up to 10 1 4 cm"2. Proton irradiation was performed at the PSI/ETH tandem accelerator at ETH Hönggerberg.

10 1 1 10 1 2 10 1 3 10 1 4

Proton Fluence §n I c m 2

Fig. 1: Ratio of efficiency after irradiation to effi­ciency before irradiation (r)0) versus proton flu­ence.

The solar cells were characterized before and after irradia­tion using standard electro-optical measurements, i.e. current-voltage characteristics under AM 1.5 irradiance, current-capacitance characteristics at 100 kHz and room temperature as well as quantum efficiency measurements. The relative efficiency as a function of the proton fluence is displayed in Fig. 1 for all three proton energies. As expected, protons of 650 keV are most damaging. For the

2.2 MeV proton irradiation of 3-10 1 2 cm"2 the efficiency is still 70% of the initial value while for 650 keV protons the efficiency dropped below 20 % at the same fluence. A part of this efficiency loss can be attributed to radiation damage (creation of color centers) in the glass substrate. Fig. 2 shows the open circuit voltage V o c as a function of irradiation fluence.

T—/A 1 1 r

Proton Fluence §n I cnr 2

Fig. 2 : V o c relative to value before irradiation as a function of proton fluence for 3 energies.

A decrease in V o c as well as in the short-circuit current J s c

(not shown here) were seen only for high fluences, above 3-10 1 2cm" 2. For smaller fluences V o c even increases by more than 2 % (20 mV in absolute value).

In conclusion, the irradiation hardness of CdTe/CdS solar cells is superior to that of mono-crystalline materials reviewed in literature. The apparent degradation observed is mainly due to transmission loss in the glass substrate. This could be avoided by using space qualified C e 0 2 doped silica fused glass. For space missions in typical orbits of communications satellites no End-Of-Lifetime degradation is expected. On the contrary, at medium proton fluences around 10 1 2 cm"2 even a slight increase in performance can be expected.

REFERENCES

[1] A. Romeo et al., MRS Symp. Proc. 668, H3.3.1 (2001).

[2] A. Romeo et al., 2nd World Conf. PVSEC, 1105 (1998).

186

AN ExB FILTER FOR THE INVESTIGATION OF LIQUID METAL ION SOURCES

R. Mühle (ETHZ); M. Döbeli (PSI)

An ExB filter with a mass resolution of 50 has been developed for the investigation of liquid metal ion sources. The filter was tested with a AuBeSi liquid metal ion source. For beam current measurements of low intensity ions the Faraday cup can be replaced with a channel plate.

A newly prepared liquid metal ion source (LMIS) has to be tested carefully before its use in a focused ion beam system [1]. For this purpose a mass spectrometer with an ExB filter has been built. It consists of the following components arranged on the ion optical axis: ion source (LMIS), electrostatic lens, mass separation aperture and Faraday cup. The LMIS can be moved parallel and in the plane perpendicular to the ion optical axis by means of a goniometer. In the case of ions of low intensity a channel plate can be inserted between aperture and Faraday cup. It can also be used for the alignment of the ion source. The temperature of the ion source can be controlled from the outside of the vacuum chamber by means of a two-colour pyrometer. The field region of the ExB filter has a length of 60 mm. The B field created by two CoSm magnets has a strength of 0.5 T. The fringe field is reduced by means of small metallic tubes on each side of the magnets as described by J. Teichert [2]. The E field is created by two electrodes, which are 5 mm apart.

The mass spectrum of an Au72Bei 4Sii4 LMIS (at-%) at a source current of 5 uA and a temperature of 500 °C, obtained with the ExB filter is shown in Fig. 1. The acceleration voltage was 5 kV. The peak current I measured in the Faraday cup is plotted against the control voltage U, which is proportional to the voltage between the E field plates and inversely proportional to the square root of the mass-to-charge ratio m/q of the ions.

120

The peak currents are shown in Tab. 1 with Au + and Au** being the strongest. The peak intensities as a function of source temperature and source current have been investigated in detail. It was found that for a fixed temperature the intensity of the doubly charged ions Be + + , S i + + and Au** decreases with decreasing source current. The same property was found by the investigation with a time-of-flight spectrometer, described in [3].

Table 1: Mass-to-charge ratio m/q and peak current I for the mass spectrum of the AuBeSi LMIS, as shown in Fig. 1.

Ion m / q I / p A

Be^ 4.51 218

Be + 9.01 32

SÍ++ 98.48 373

Si+ 14.04 26

Au++ 28.09 656

Au+ 196.97 1953

Au 2

+ 393.93 92

Au 3

+ 590.90 21

Au 4

+ 787.87 0.7

Au 5

+ 984.83 0.8

4.80

REFERENCES

[1] R. Mühle, Rev. Sei. Instrum. 63, 3040 (1992).

[2] J. Teichert, Arbeiten zum Wienfilter und zur CoNd-LMIS, Arbeitsbericht Mai 1992, FZR Rossendorf (1992).

[3] R. Mühle, M. Döbeli and C. Maden, J. Phys. D: Appl. Phys. 32, 161 (1999).

Fig. 1: Mass spectrum of the Au72Be 1 4 Si 1 4 LMIS (at-%) at a source current of 5 uA and a temperature of 500 °C. The current of intensive peaks has been scaled by the factor shown in brackets.

The peaks of the singly and doubly charged ions of the isotopes Si, Si and Si are resolved nicely. Investigations on a GePd LMIS have shown that the mass resolution of the filter is about 50.

187

LIST OF PUBLICATIONS

LABORATORY FOR PARTICLE PHYSICS

R-86-05 H. -Ch. Schröder, A. Badertscher, R F. A. Goudsmit, M. Janousch, H. J. Leisi, E. Matsinos, D. Sigg, Z. G. Zhao, D. Chatellard, J. -P. Egger, K. Gabathuler, P. Hauser, L. M. Simons, A. J. Rusi El Hassani, The pion-nucleon scattering lengths from pionic hydrogen and deuterium Eur. Phys. J. C 21,473 (2001).

R-87-13 B. Kothnski, D. Androic, G. Backenstoss, D. Bosnar, T. Dooling, M. Furie, P. A. M. Gram, N. K. Gregory, A. Hoffart, C. H. Q. Ingram, A. Klein, K. Koch, J. Köhler, M. Kroedel, G. Kyle, A. Lehmann, V. Markushin, A. O. Mateos, K. Michaelian, T. Petkovic, M. Planinic, R. P. Redwine, D. Rowntree, N. Simicevi,' R. Trezeciak, HJ. Weyer, M. Wildi, K. E. Wilson, Pion absorption reactions on N, Ar and Xe Eur. Phys. J. A 9, 537 (2000).

R94-10.1 I. C. Barnetter a / . , X. Morelle, An apparatus for the measurement of the transverse polarization of positrons from the decay of polarized muons Nucl. Instrum. Meth. A 455,329 (2000).

R-96-04 K. Bodek, T. Boehm, D. Cond, N. Danneberg, W. Fetscher, C. Hilbes, M. Janousch, St. Kistryn, K. Köhler, J. Lang, M. Markiewicz, J. Sromicki and J. Zejma, A tracking detector for low energy electrons Nucl. Instrum. Meth.A 473, 326 (2001).

R-96-05 F. Atchison, M. Daum, P.-R. Kettle and C. Wigger, Does the KARMEN time anomaly originate from a beam correlated background? Phys. Lett. B 498,11 (2001).

R-98-03 J. F. C. A. Veloso, J. M. F. dos Santos, C. A. N. Conde, F. Mulhauser, P. Knowles, C. Donche-Gay, O. Huot, D. Taqqu, F. Kottmann, A driftless gas proportional scintillation counter for muonic hydrogen X-ray spectroscopy under strong magnetic fields Nucl. Instrum. Meth. A 460,297 (2001).

Z-01-03 M. Pajek, D. Bañas, D. Castella, D. Corminboeuf, J.-Cl. Dousse, Y.-P. Maillard, O. Mauron, P.-A. Raboud, D. Chmielewska, I. Fijal, M. Jaskola, A. Korman, T. Ludjiejewski, J. Rzadkiewicz, Z. Sujkowski, J. Hoszowska, M. Polasik and T. Mukoyama, High-resolution measurements ofTh and U x-rays induced by energetic ions Phys. Scripta T 92, 382 (2001).

E-91-09 T. A. Porcelli, A. Adamczak, J. M. Bailey, G. A. Beer, J. L. Douglas, M. P. Faifman, M. C. Fujiwara, T. M. Huber, P. Kammel, S. K. Kim, P. E. Knowles, A. R. Kunselman, M. Maier, V. E. Markushin, G. M. Marshall, G. R. Mason, F. Mulhauser, A. Olin, C. Petitjean, J. Zmeskal, Measurement of the Resonant dpt Molecular Formation Rate in Solid HD Phys. Rev. Lett. 86, 3763 (2001).

PIBETA COLLABORATION, PSI E. Frlez, D. Pocanic, and S. Ritt, ADC common noise correction and zero suppression in the PIBETA detector Nucl. Instrum. Meth. A 463,341 (2001).

188

E. Frlez, Ch. Brönnimann, B. Krause, D. Pocanic, D. Renker, S. Ritt, P. L. Slocum, I. Supek, and H. P. Wirtz, Light Response of pure Csl calorimeter crystals painted with wavelength shifting lacquer Nucl. Instrum. Meth. A 459,426 (2001).

E. Frlez, B. K. Wright, and D. Pocanic, Optics: general-purpose scintillator light response simulation code Comp. Phys. Commun. 134, 110 (2001).

BROOKHAVEN AGS, E865 COLLABORATION J. Egger, W. Herold, H. Kaspar, S. Pislak et al., New Measurement ofK^4 Decay and the s-Wave irir-Sacttering Length OQ Phys. Rev. Lett. 87, 221801-1 (2001).

CERN, L3 Collaboration M. Acciarri et ai, A. J. Barczyk, K. Deiters,

Measurement of the topological branching fractions of the tau lepton at LEP Phys. Lett. B 519,189 (2001).

Standard model Higgs boson with the L3 experiment at LEP Phys. Lett. B 517, 319 (2001).

Search for heavy neutral and charged leptons in e+e~ annihilation at LEP Phys. Lett. B 517,75 (2001).

Search for heavy isosinglet neutrino in e+e~ annihilation at LEP Phys. Lett. B 517,67 (2001).

Total cross section in 7 7 collisions at LEP Phys. Lett. B 519, 33 (2001).

Study of the e+e~ —> Z 7 7 —>• 5 5 7 7 process at LEP Phys. Lett. B 505,47 (2001).

Measurement of the tau branching fractions into leptons Phys. Lett. B 507,47 (2001).

Measurement of the charm production cross section in 7 7 collisions at LEP Phys. Lett. B 514,19 (2001).

Search for the standard model Higgs boson in e+e~ collisions at i / i up to 202-GeV Phys. Lett. B 508,225 (2001).

Search for neutral Higgs bosons of the minimal supersymmetric standard model in e+e~ interactions at sfs = 192 GeV to 202 GeV Phys. Lett. B 503,21 (2001).

Measurements of the cross sections for open charm and beauty production in ^collisions at i / i = 189 GeV - 202 GeV Phys. Lett. B 503,10 (2001).

Search for excited leptons in e+e~ interactions at \ÍS = 192 GeV - 202 GeV Phys. Lett. B 502, 37 (2001).

Search for R-parity violating decays of supersymmetric particles in e+e~ collisions at i/s = 189 GeV Eur. Phys. J. C 19, 397 (2001).

Higgs candidates in e+e~ interactions at i/s = 206.6 GeV Phys. Lett. B 495,18 (2000).

189

Kg Kg final state in two-photon collisions and implications for glueballs Phys. Lett. B 501,173 (2001).

Light resonances in Ks A ' ~ 7 r ± and r¡TT+TT~ final states in ^y^collisions at LEP Phys. Lett. B 5 0 1 , 1 (2001).

CERN, CPLEAR COLLABORATION A. Angelopoulos et al., P. Bargassa, F. Blanc, P.-R. Kettle, T. Nakada, O. Wigger, T-violation and CPT-invariance measurements in the CPLEAR experiment: A detailed description of the analysis of neutral-kaon decays to e irv Eur. Phys. J. C 22,55 (2001).

K° # K° transitions monitored by strong interactions: A new determination of the KL — Ks mass difference Phys. Lett. B 503,49 (2001).

CERN, CMS COLLABORATION K. Deiters, Q. Ingram, D. Renker, S. Reucroft, T. Sakhelashvili, M. Diemoz et al., Investigation of the avalanche photodiodes for the CMS electromagnetic calorimeter operated at high gain Nucl. Instrum. Meth A 461,574 (2001).

K. Deiters, Q. Ingram, D. Renker, T. Sakhelashvili, Y. Musienko et al., Properties of the most recent avalanche photodiodes for the CMS electromagnetic calorimeter Nucl. Instrum. Meth. A 442,193 (2000).

Properties of the avalanche photodiodes for the CMS electromagnetic calorimeter Nucl. Instrum. Meth. A 453,223 (2000).

DESY, HI COLLABORATION C. Adloffetal., S. Egli, R. Eichler, K. Gabathuler, J. Gassner, R. Horisberger

D*^ meson production in deep inelastic diffractive interactions at HERA Phys. Lett. B 520,191 (2001).

On the rise of the proton structure function F 2 towards low X Phys. Lett. B 520,183 (2001).

A search for leptoquark bosons in e-p collisions at HERA Phys. Lett. B 523,234 (2001).

Measurement of deeply virtual Compton scattering at HERA Phys. Lett. B 517,47 (2001).

Three jet production in deep inelastic scattering at HERA Phys. Lett. B 515,17 (2001).

Photoproduction with a leading proton at HERA Nucl. Phys. B 619, 3 (2001).

Searches at HERA for squarks in R-parity violating supersymmetry Eur. Phys. J. C 20,639 (2001).

CMS-PIXEL GROUP R. Baur Readout architecture of the CMS pixel detector Nucl. Instrum. Meth. A 465,159 (2001).

190

K. Gabathuler, R. Horisberger, ROSE-Collaboration Developments for radiation hard silicon detectors by defect engineering Nucl. Instrum. Meth. A 465,60 (2001).

K. Gabathuler, R. Horisberger, ROSE-Collaboration Radiation hard silicon detectors Nucl. Instrum. Meth. A 466,308 (2001).

R. Horisberger, R. Kaufmann, CMS-Pixel Collaboration Design and test of pixel sensors for the CMS experiment Nucl. Instrum. Meth. A 461,182 (2001).

R. Horisberger Readout architectures for pixel detectors Nucl. Instrum. Meth. A 465,148 (2001).

D. Kotlinski The CMS pixel detector Nucl. Instrum. Meth. A 465,46 (2001).

THEORY GROUP C. Alexandroue, P. de Forcrand and E. Follane, The gluon propagator without lattice Gribov copies Phys. Rev. D 63,094504 (2001).

A. Badertscher, M. Daum, P. F. A. Goudsmith, M. Janousch, P.-R. Kettle, J. Koglin, V. E. Markushin, J. Schottmüller and Z. G. Zhao, Experimental verification of Coulomb de-excitation in pionic hydrogen Europhys. Lett. 54, 313(2001).

W. Beenakker, S. Dittmaier, M. Krämer, B. Plumper, M. Spira and P. M. Zerwas, Higgs radiation off top quarks at the Tevatron and the LHC Phys. Rev. Lett. 87, 201805 (2001).

M. Böhm, A. Denner and H. Joos, Gauge theories of the strong and electroweak interaction Teubner (2001), 784 p.

A. Denner and S. Pozzorini, One loop leading logarithms in electroweak radiative corrections. 1. Results Eur. Phys. J. C 18,461 (2001).

A. Denner and S. Pozzorini, One loop leading logarithms in electroweak radiative corrections. 2. Factorization ofcollinear singularities Eur. Phys. J. C 21,63 (2001).

A. Denner, S. Dittmaier, M. Roth and D. Wackeroth, Probing anomalous quartic gauge boson couplings via e+e~ —> 4 fermions + 7 Eur. Phys. J. C 20, 201 (2001).

S. Dürr, QCD in a finite box: numerical test studies in the three Leutwyler-Smilga regimes Nucl. Phys. B 594,420 (2001).

S. Dürr, Topological susceptibility in full QCD: lattice results versus the prediction from the QCD partition function with granularity Nucl. Phys. B 611 , 281 (2001).

191

V. A. Kuzmin, T. V. Tetereva, K. Junker, Calculation of the total rates of muon capture by complex nuclei

Izvestiya RAN, ser:fizich, Vol.65,40 (2001) (engl, transi.: Bulletin of the Russian Academy of Science, phys.ser.).

M. Melles, Subleading Sudakov logarithms in electroweak high-energy processes to all orders Phys. Rev. D 63,034003 (2001). M. Melles, Resummation of Yukawa enhanced and subleading Sudakov logarithms in longitudinal gauge boson and Higgs production Phys. Rev. D 64,014011 (2001).

M. Melles, Electroweak renormalization group corrections in high-energy processes Phys. Rev. D 64,054003 (2001).

M. M. Mühlleitner, M. Krämer, M. Spira and P. M. Zerwas, Production ofMSSM Higgs bosons in photon-photon collisions Phys. Lett. B 508,311 (2001).

T. A. Porcelli et al., V. E. Markushin, Measurement of the resonant dpt molecular formation rate in solid HD, Phys. Rev. Lett. 86, 3763 (2001).

R. Rosenfelder and A. W. Schreiber, On the best quadratic approximation in Feynman 's path integral treatment of the polaron Phys. Lett. A 284,63 (2001).

192

LABORATORY FOR ASTROPHYSICS

K. Arzner, M. Scholer, Kinetic structure of the post-plasmoid plasma sheet during magnetotail reconnection J. Geophys. Res. 106 A 3, 3827 (2001).

K. Arzner, M. Scholer, Magnetotail reconnection: simulation predictions on magnetic time series Earth Planets Space 53, 655 (2001).

M. Audard, M. Güdel, R. Mewe, The XMM-Newton View of Stellar Coronae: Flare Heating in the Coronae of HR 1099 Astron. Astrophys. 365, L318 (2001).

M. Audard, E. Behar, M. Güdel, A. J. J. Raassen, D. Porquet, R. Mewe, C. R. Foley, G. E. Bromage, The XMM-Newton View of Stellar Coronae: High-Resolution X-Ray Spectroscopy of Capella. Astron. Astrophys. 365, L329 (2001).

E. Behar, A. P. Rasmussen, R. G. Griffiths, K. Dennerl, M. Audard, B. Aschenbach, A. C. Brinkman, High-Resolution X-Ray Spectroscopy and Imaging of Supernova Remnant N132D Astron. Astrophys. 365, L242 (2001).

I. A. Bonnell, K. W. Smith, M. B. Davies, K. Home, Planetary dynamics in stellar clusters Mon. Not. R. Astron. Soc. 322, 859 (2001).

A. C. Brinkman, E. Behar, M. Güdel, M. Audard, A.J. F. den Boggende, G. Branduardi-Raymont, J. Cottam, C. Erd, J. W. den Herder, F. Jansen, J. S. Kaastra, S. M. Kahn, R. Mewe, F. B. S. Paerels, J. R. Peterson, A. P. Rasmussen, I. Sakelliou, C. de Vries, First Light Measurements with the XMM-Newton Reflection Grating Spectrometers: Evidence for an Inverse First Ionisation Potential Effect and Anomalous Ne Abundance in the Coronae of HR 1099 Astron. Astrophys. 365, L324 (2001).

A. Decourchelle, J. L. Sauvageot, M. Audard, B. Aschenbach, S. Sembay, R. Rothenflug, J. Ballet, T. Stadlbauer, R. G. West, XMM-Newton Observation of the Tycho Supernova Remnant Astron. Astrophys. 365, L218 (2001).

M. Güdel, M. Audard, K. Briggs, H. Magee, A. Maggio, R. Mewe, R. Pallavicini, J. Pye, The XMM-Newton View of Stellar Coronae: X-Ray Spectroscopy of the Corona of AB Doradus Astron. Astrophys. 365, L336 (2001).

M. Güdel, M. Audard, H. Magee, E. Franciosini, N. Grosso, F. Cordova, R. Pallavicini, R. Mewe, The XMM-Newton View of Stellar Coronae: Coronal Structure in the Castor X-Ray triplet Astron. Astrophys. 365, L344 (2001).

J. W. den Herder, A. C. Brinkman, S. M. Kahn, G. Branduardi-Raymont, K. Thomsen, H. Aarts, M. Audard, J. V. Bixler, A. J. F. den Boggende, J. Cottam, T. Decker, L. Dubbledam, C. Erd, H. Goulooze, M. Güdel, P. Guttridge, C. J. Hailey, K. al Janabi, J. S. Kaastra, P. A. J. de Korte, B. J. van Leeuwen, C. Mauche, A. J. McCalden, R. Mewe, A. Naber, F. B. S. Paerels, J. R. Peterson, A. P. Rasmussen, K. Rees, I. Sakelliou, M. Sako, J. Spodek, M. Stern, T. Tamura, J. Tandy, C. P. de Vries, S. Welch, A. Zehnder, The Reflection Grating Spectrometer on board XMM-Newton Astron. Astrophys. 365, L7 (2001).

S. M. Kahn, M. A. Leutenegger, J. Cottam, G. Rauw, J.-M. Vreux, A. J. F. den Boggende, R. Mewe, M. Güdel, High-Resolution X-Ray Spectroscopy ofC, Puppis with the XMM-Newton Reflection Grating Spectrometer Astron. Astrophys. 365, L312 (2001).

193

G. Paesold, A. O. Benz, K.-L. Klein, N. Vilmer, Spatial analysis of solar type III events associated with narrowband spikes at metric wavelength Astron. Astrophys. 371, 333 (2001).

P. Schuecker, H. Boehringer, K. Arzner, T. Reiprich, Cosmic Mass functions from Gaussian stochastic diffusion processes Astron. Astrophys. 370,715-728 (2001).

S. L. Skinner, M. Güdel, W. Schmutz, I. R. Stevens, Chandra HETG Spectra of^j2 Velorum Astrophys. J. 558, LI 13 (2001).

K. W. Smith, G. F. Lewis, I. A. Bonnell, J. P. Emerson, Inf all variability in the classical T Tauri system VZ Cha Astron. Astrophys. 378,1003 (2001).

K. W. Smith, I. A. Bonnell, Free-floating planets in stellar clusters? Mon. Not. R. Astron. Soc. 322, LI (2001).

194

LABORATORY FOR MUON SPIN SPECTROSCOPY

RA-90-03 A. M. Mulders, R C. M. Gubbens, C. T. Kaiser, A. Amato, F. N. Gygax, A. Schenck, P. Dalmas de Réotier, A. Yaouanc, K. H. J. Buschow, F. Kayzel, A. A. Menovsky, Muon spin dynamics and sites in GdNi$ Hyperfine Interactions 133,197 (2001).

RA-93-05 D. Baabe, H. H. Klauss, W. Kopmann, M. Birke, D. Mienert, F. J. Litterst, P. Adelmann, and F. Z. Litterst, Inhomogeneous magnetism in electron doped cuprates J.Magn.Magn.Mat.226,95 (2001).

RA-93-06 S. J. Blundell, I. M. Marshall, B. W. Lovett, F. L. Pratt, A. Husmann, W. Hayes, S. Takagi, T. Sugano, Organic magnetic materials studied by positive muons Hyperfine Interactions 133,169 (2001).

S. J. Blundell, Muon-spin rotation studies of molecule based magnets In Magnetism: Molecules to Materials, ed. J. S. Miller and M. Drillon, (Wiley-VCH, Weinheim, 2001 (ISBN 3-527-29772-3)), p235.

M. Kurmoo, H. Kumagai, M. A. Green, B. W. Lovett, S. J. Blundell, A. Ardavan, J. Singleton, Two Modifications of Layered Cobaltous Terephthalate: Crystal Structures and Magnetic Properties J. Solid State Chem. 159,343 (2001).

T. Sugano, S. J. Blundell, W. Hayes, P. Day, Magnetism in organic radical ion salts and complexes based on nitronyl nitroxide Synth. Met. 121,1812 (2001).

F. L. Pratt, S. L. Lee, C. M. Aegerter, C. Ager, S. H. Lloyd, S. J. Blundell, F. Y. Ogrin, E. M. Forgan, H. Keller, W. Hayes, T. Sasaki, N. Toyota, S. Endo, pSR studies of the flux vortex phases in a BEDT-TTF superconductor Synth. Met. 120,1015 (2001).

I. M. Marshall, F. L. Pratt, S. J. Blundell, W. Hayes, A pSR study of the CDWin TTF-TCNQ Synth. Met. 120,997 (2001).

T. Jestädt, M. Kurmoo, S. J. Blundell, F. L. Pratt, C. J. Kepert, K. Prassides, B. W. Lovett, I. M. Marshall, A. Husmann, K. H. Chow, R. M. Valladares, C. M. Brown, A. Lappas, Muon-spin-rotation and magnetization study of metal-organic magnets based on the dicyanamide anion J. Phys.: Condens. Matter 13, 2263 (2001).

S. J. Blundell and S. F. J. Cox, Longitudinal muon spin relaxation in metals and semimetals and the Korringa law J. Phys.: Condens. Matter 13, 2163 (2001).

RA-93-12 S. J. Blundell, F. L. Pratt, I. M. Marshall, A. Husmann, W. Hayes, R. Martin, A. B. Holmes, Muon-spin relaxation study of charge carrier dynamics in the conducting polymer PPV Synth. Met. 119,205 (2001).

RA-94-03 D. E. MacLaughlin, O. O. Bernai, R. H. Heffner, G. J. Nieuwenhuys, M. S. Rose, J. E. Sonier, B. Andraka, R. Chau, M. B. Maple, Glassy spin dynamics in non-Fermi-liquid UCu^-xPdx, x = 1.0 and 1.5 Phys. Rev. Lett. 87,066402 (2001).

195

RA-94-04 F. L. Pratt, S. L. Lee, C. M. Aegerter, C. Ager, S. H. Lloyd, S. J. Blundell, F. Y. Ogrin, E. M. Forgan, H. Keller, W. Hayes, T. Sasaki, N. Toyota, S. Endo, pSR Studies of the Flux Vortex Phases in a BEDT-TTF Superconductor Synth. Met. 120,1015 (2001).

PvA-94-14 G. Solt, Phase diagram for Condon domains in beryllium Solid State Commun. 118, 231 (2001).

PvA-97-12 P. W Klamut, B. Dabrowski, S. Mini, M. Maxwell, S. Kolesnik, M. Mais, A. Shengelaya, R. Khasanov, I. Savic and H. Keller, Magnetic properties of RuSr2RECii20$ (RE=Gd, Eu) and Rui-xSr2GdCu2+xO$-y superconductors Physica C 364, 313 (2001).

RA-97-19 P. D. Battle, A. M. T. Bell, S. J. Blundell, A. I. Coidea, E. J. Cussen, G. C. Hardy, I. M. Marshall, M. J. Rosseinsky and C. A. Steer, Chemically induced magnetism and magnetoresistance in Lao.sSr1.2Mno.eRho.4O4 J. Am. Chem. Soc. 123,7610 (2001).

RA-97-22 B. W. Lovett, S. J. Blundell, J. Stießberger, F. L. Pratt, T. Jestädt, S. P. Cottrell, I. D. Reid, Molecular dynamics in a nematic liquid crystal probed by positive muons Phys. Rev. B 63,054204 (2001).

RA-97-23 J. M. Gil, H. V. Alberto, R. C. Viläo, J. Piroto Duarte, N. Ayres de Campos, A. Weidinger, J. Krauser, E. A. Davis, S. P. Cottrell, S. F. J. Cox, Shallow donor muonium states in II-VI semiconductor compounds Phys. Rev. B 64,075205 (2001).

J. M. Gil, H. V. Alberto, R. C. Viläo, J. Piroto Duarte, N. Ayres de Campos, A. Weidinger, E. A. Davis, S. F. J. Cox, Muonium states in HgO J. Phys.: Condens. Matter 13, L613 (2001).

S. F. J. Cox, E. A. Davis, P. J. C. King, J. M. Gil, H. V. Alberto, R. C. Viläo, J. Piroto Duarte, N. Ayres de Campos, R. L. Lichti, Shallow versus deep hydrogen states in ZnO and HgO J. Phys.: Condens. Matter 13, 9001 (2001).

RA-97-24 I. Z. Machi, S. H. Connell, J. P. F. Sellschop and K. Bharuth Ram, Muon(ium) in nitrogen-rich (type la) and 13C diamonds In Proceedings of the International Conference on Fundamental and Applied Aspects of Modern Physics, edited by S. H. Connell and R. Tegen (World Scientific, 2001).

RA-97-25 T. N. Mamedov, D. G. Andrianov, D. Herlach, V. N. Gorelkin, K. I. Gritsai, O. Kormann, J. Major, A. V. Stoikov, U. Zimmermann, The relaxation rate of the magnetic moment of a shallow acceptor center as a function of impurity concentration in silicon JETP92,1004(2001).

T. N. Mamedov, D. G. Andrianov, D. Herlach, V. N. Gorelkin, K. I. Gritsai, V. N. Duginov, O. Kormann, J. Major, A. V. Stoikov, U. Zimmermann, Magnetic moment relaxation of a shallow acceptor center in heavily doped silicon JETPLett. 73,674 (2001).

T. N. Mamedov, D. Herlach, K. I. Gritsai, O. Kormann, J. Major, A. V. Stoikov, U. Zimmermann, Measurements of the magnetic moment of the negative muon in the bound state in various atoms JETP93,941 (2001).

196

RA-98-04 R. H. Heffner, J. E. Sonier, D. E. MacLaughlin, G. J. Nieuwenhuys, G. M. Luke, Y. J. Uemura, W. Ratcliff, S. W. Cheong, and G. Balakrishnan, Muon spin relaxation study of Lai-xCaxMnOs Phys.Rev. B 63,094408 (2001).

RA-98-07 D. Andreica, A. Amato, F. N. Gygax, A. Schenck, G. Wiesinger, C. Reichl and E. Bauer, LiSR studies of the nonmagnetic-magnetic transition in YbCu^-xAlx

J. Magn. Magn. Mat. 226,129 (2001).

RA-98-10 H.-H. Klauß, W. Wagener, B. Büchner, M. Hücker, D. Mienert, W. Kopmann, M. Birke, H. Luetkens, D. Baabe, F. J. Litterst, Charge carrier dynamics in Zn-doped cuprates Hyperfine Interactions 133 ,203 (2001).

RA-98-17 S. F. J. Cox, M. Charlton, P. Donnelly, A. Amato and A. Schenck, The neutral fraction of muonium in silicon at high temperatures J.Phys.: Condens. Matter 13,2155 (2001).

RA-98-20 B. Roessli, U. Staub, A. Amato, D. Herlach, P. Pattison, K. Sablina and G. A. Petrakovskii, Magnetic phase transitions in the double spin-chains compound LiCu^O^ Physica B 296, 306 (2001).

RA-99-01 D. Mienert, H.-H. Klauß, D. Baabe, W. Kopmann, F. J. Litterst, U. Ammerahl, B. Büchner, Magnetic correlations in the spin chains of Sri.hCaw.^CuiiO\\ studied by Lisr

J. Magn. Magn. Mat. 226,452 (2001).

I. Maksimov, D. Baabe, H.-H. Klauß, F. J. Litterst, R. Feyerherm, D. M. Tobbens, A. Matsushita, S. Süllow, Structure and magnetic order in Fe2+X Vi_xAl J. Phys.: Condens. Matter. 13, 5487 (2001).

RA-99-06 M. C. Guidi, G. Allodi, R. De Renzi, G. Guidi, M. Hennion, L. Pinsard and A. Amato, Staggered magnetization, critical behavior, and weak ferromagnetic properties ofhaMnOz by muon spin rotation Phys. Rev. B 64,064414 (2001).

RA-99-09 V. S. Egorov, G. Soit, C. Baines, D. Herlach, U. Zimmermann, Superconducting intermediate state in white tin studied by muon-spin-rotation spectroscopy Phys. Rev. B 64,024524 (2001).

RA-00-02 C. Bernhard, J. L. Talion, T. Blasius, A. Golnik, and C. Niedermayer, Anomalous peak in the superconducting condensate density ofcuprate high-Tc superconductors at a unique doping state Phys. Rev. Lett. 86, 1614 (2001).

Y. Sidis, C. Ulrich, P. Bourges, C. Bernhard, C. Niedermayer, L. P. Regnault, N. H. Andersen and B. Keimer, Antiferromagnetic ordering in superconducting YBa^Cu^O^.c, Phys. Rev. Lett. 86, 4100 (2001).

RA-00-10 G. A. Petrakovskii, K. S. Aleksandrov, L. N. Bezmaternikh, S. S. Aplesnin, B. Roessli, F. Semadeni, A. Amato, C. Baines, J. Bartolome and M. Evangelisti, Spin-glass state in CuGai 0\ Phys. Rev. B 63,184425 (2001).

197

F. Semadeni, A. Amato, B. Roessli, R B o n i , C. Baines, T. Masuda, K. Uchinokura and G. Shirane, Macroscopic and local magnetic moments in Si-doped CuGeO-¡ as determined by neutron and muSR studies Eur. Phys. J. B 21, 307 (2001).

RA-01-07 A. Schenck, D. Andreica, F. N. Gygax, K. Umeo, T. Takabatake, E. Schreier, A. Kratzer, G. M. Kalvius, Muon Spin Rotation study of Ce^Ni?,: muon related and intrinsic properties of the paramgnetic phase J. Phys.: Condens. Matter 13,4277 (2001).

RA-01-26 A. M. Lossack, E. Roduner, D. M. Bartels, Solvation and kinetic isotope effects in H and D abstraction reactions from formate ions by D, H and Mu atoms in aqueous solution Phys. Chem. Chem. Phys. 3, 2031 (2001).

E. Roduner, H. Dilger, Acid Catalysis in HZSM-5: The Role Of Entropy J. Am. Chem. Soc. 123,7717 (2001).

198

LABORATORY FOR MICRO A N D NANO TECHNOLOGY

B. Baumeister, T. Jung, E. Meyer Nanoscale fracture studies using the scanning force microscope Appl. Phys. Lett. 78, 2485 (2001).

B. Baumeister, T. Jung, E. Meyer Tribological studies on fracture and erosion of nano structure s Tribol. Lett. 11,107 (2001).

S. Berner, M. Brunner, L. Ramoino, H. Suzuki, H.-J. Giintherodt, T.A. Jung Time evolution analysis of a 2D solid-gas equilibrium: A system for molecular adsorption and diffusion Chem. Phys. Lett. 348,175 (2001).

B. Bitnar, W. Durisch, D. Grützmacher, J.-C. Mayor, F. von Roth, J.A. Anna Selvan, H. Sigg, H. R. Tschudi, J. Gobrecht A TPV system with silicon photocells and a selective emitter

Proc. 28 t h IEEE Photovoltaic Spec. Conf. 2000, Inst, of Electrical and Electronics Eng., 1218 (2001).

S. Blaser, L. Diehl, M. Beck, J. Faist, U. Oesterle, J. Xu, S. Barbieri, F. Bertram Characterization and modelling of quantum cascade lasers based on a photon-assisted tunneling transition IEEE J. Quantum Electron. 37,448 (2001). N. E. A. Crompton, J. Gobrecht, C. Higgs, G. Kühne, E. Lehmann, H. Reist, J. Stepanek, T. Tsuda, B. Larsson, Case-Mate: Computer-aided cell seeding, micro-cloning, analysis and telemetric evaluation applied to neutron capture therapy "Frontiers in Neutron Capture Therapy", ed. by Hawthorne et al., Kluwer Academic/Plenum Publishers, New York, 231 (2001).

C. David, D. Wiesmann, R. Germann, F. Horst, B. J. Offrein, R. Beyeler, H.W.M. Salemink, G. L. Bona Apodised Bragg gratings in planar waveguides for add-drop filters Microelectronic Engineering 57-58,713 (2001).

C. David, J. Wei, T. Lippert, A. Wokaun Diffr active grey tone masks for laser ablation lithography Microelectronic Engineering 57-58,453 (2001).

C. David, E. Ziegler, B. Nöhammer Wet etched diffr active lenses for hard x-rays Journal of Synchrotron Radiation 8,1054 (2001).

C. David, B. Nöhammer, E. Ziegler A wavelength tunable diffractice transmission lens for hard x-rays App. Phys. Lett. 79,1088 (2001).

C. David, B. Nöhammer, E. Ziegler, O. Hignette Tunable diffr active optical elements for hard x-rays Proceedings of the SPIE - The International Society for Optical Engineering 4499,96 (2001).

C. David, B. Nöhammer, H. Solak, B. Haas, F. Glaus, J. F. van der Veen, V. Schlott, J. Bongaerts, B. Kaulich, J. Susini Diffractive x-ray lenses for photon energies ranging from extreme ultraviolett to hard x-rays Proceedings of the SPIE - The International Society for Optical Engineering 4499, 85 (2001).

G. Dehlinger, L. Diehl, U. Gennser, H. Sigg, J. Faist, K. Ensslin, D. Grützmacher, E. Müller Intersubband-Electroluminescencefrom Si/SiGe Quantum Cascade Structures Part of the SPIE Conf. on Silicon-based Optoelectronics, San Jose, California, January 2001, Proc. SPIE, Silicon-based and Hybrid Optoelectronics III, eds. David J. Robbins, John A. Trezza, Ghassan E. Jabbour, Vol. 4293,79 (2001).

U. Dötsch, U. Gennser, C. David, G. Dehlinger, D. Grützmacher, T. Heinzel, S. Lüscher, K. Ensslin A single hole transistor in a p-Si/SiGe quantum well Applied Physics Letters 78, 341 (2001).

199

U. Dötsch, V. Senz, U. Gennser, T. Heinzel, T. Ihn, S. Lüscher, K. Ensslin, G. Dehlinger, C. David, D. Grützmacher Electrical conductivity of strongly interacting holes in 2D and OD "Electronic Correlations: from Meso- to Nanophysics", eds.: T. Martin, G. Montambaux, J. Trän Thanh V a n , EDPSciences, 207 (2001).

H. Elgamel, J. Gobrecht A simple and efficient process for fabricating high efficiency polycrystalline silicon ribbon solar cells Solar Energy Materials and Solar Cells, Esevier Science Publishers 65,561 (2001).

M. Folkard, G. Schettino, B. Vojnovic, A. G. Michette, C. David, K.M. Prise, B.D. Michael Development and application of a focused ultrasoft X-ray probe for radiobiological applications Proceedings of the SPIE - The International Society for Optical Engineering 4499,10 (2001).

J. Gobrecht, L. Tiefenauer Nanostrukturierte Oberflächen für die Bioanalytik 3. Symp. "Neue Technologien für die Medizin", ed. by M. Weck, Shaker, Aachen, 407 (2001).

A. Grubelnik, C. Padeste. L. Tiefenauer Highly sensitive enzyme immunoassay (EIA) for detection of benzylpenicillin in milk Food & Agriculture Immunol. 13, 161 (2001).

C. Guedj, A. Beyer, E. Müller, D. Grützmacher Raman spectroscopy of carbon-induced germanium dots Appl. Phys. Lett. 78,1742 (2001).

L. J. Heyderman, H. Schift, C. David, B. Ketterer, M. Auf der Maur, J. Gobrecht Nanofabrication using hot embossing lithography and electroforming Microelectronic Eng. 57-58,375 (2001).

T. Lippert, C. David, M. Hauer, C. Phipps, A. Wokaun Taylor-Made Polymers for Laser Ablation The Review of Laser Engineering 29,734 (2001).

E. Müller, O. Kirfel, A. Rastelli, H. von Känel, D. Grützmacher Investigation of the early stages of Si-overgrowth of Ge-dots on Si(001) Conf. Proceedings, Microscopy of Semiconductor Materials XII, Oxford, U.K. (2001).

B. Müller, M. Riedel, R. Michel, S. De Paul, R. Hofer, D. Heger, D. Grützmacher The impact of nanometer-scale roughness on contact-angle hysteresis and globulin adsorption J. Vac. Sei. Technol. 19,1715 (2001).

V.Ya. Prinz, D. Grützmacher, A. Beyer, C. David, B. Ketterer, E. Deckardt A new technique for fabricating three-dimensional micro- and nanostructures of various shapes Nanotechnology 12, 399 (2001).

T. Prokscha, E. Morenzoni, C. David, A. Hofer, H. Glückler, L. Scandeila Moderator gratings for the generation of epithermal positive muons Applied Surface Science 172, 235 (2001).

H. Schift, L J. Heyderman, M. Auf der Maur, J. Gobrecht Pattern formation in hot embossing of thin polymer films Nanotechnology 12,173 (2001).

C. Schulze-Briese, B. Ketterer, C. Pradervand, Ch. Brönnimann, C. David, R. Horisberger, A. Puig-Molina, H. Graafsma A CVD-diamond based beam profile monitor for undulator radiation Nucl. Instrum. Meth. A 467-468, 230 (2001).

H. Sigg, G. Dehlinger, L. Diehl, U. Gennser, S. Stutz, J. Faist, D. Grützmacher, K. Ensslin, E. Müller Valence band intersubband electroluminescence from Si/SiGe quantum casade structures Physica E 11,240 (2001).

200

H. H. Solak, Y. Yang, F. Cerrina Observation of speckle patterns in extreme ultraviolet imaging J. Vac. Sei. Technol. B 19, 2406 (2001).

H. H. Solak, Y. Vladimirsky, F. Cerrina, B. Lai, W. Yun, Z. Cai, P. Ilinski, D. Legnini, W. Rodrigues Measurement of strain in Al-Cu interconnect lines with x-ray microdiffraction APS Forefront 1, 6 (2001).

H. Sorribas, D. Braun, L. Leder, P. Sonderegger, L. Tiefenauer Adhesion proteins for a tight neuron-electrode contact J. Neuroscience Methods 104, 133 (2001).

H. Sorribas, L. Tiefenauer, J. Gobrecht System for extracellular recording of electrical signals from in-vitro cultivated neurons Biomedizinische Technik 46,438 (2001).

201

L A B O R A T O R Y F O R R A D I O - A N D E N V I R O N M E N T A L C H E M I S T R Y

H E A V Y E L E M E N T S H.W. Gäggeler, U. Krähenbühl The Laboratory of Radiochemistry at Bern University and the Paul Scherrer Institute Chimia 55,1017 (2001).

H. Haba, K. Tsukada, M. Asai, I. Nishinaka, M. Sakamoto, S. Goto, M. Hirata, S. Ichikawa, Y. Nagame, T. Kaneko, H. Kudo, A. Toyoshima, Y. Shoji, A. Yokoyama, A. Shinohara, Y. Oura, K. Sueki, H. Nakahara, M. Schädel, J.V. Kratz, A. Türler, H.W. Gäggeler Startup ofTransactinide Chemistry in JAERI Radiochim. Acta 11/12, in press (2001).

S. Hübener, S. Taut, A. Vahle, R. Dressler, B. Eichler, H.W. Gäggeler, D.T. Jost, D. Piguet, A. Türler, W. Büchle, E. Jäger, M. Schädel, E. Schimpf, U. Kirbach, N. Trautmann, A.B. Yakushev Physico-Chemical Characterization of Seaborgium as Oxide Hydroxide Radiochim. Acta 11/12, in press (2001).

A.B. Yakushev, G.V. Buklanov, M.L. Chelnokov, V.l. Chepigin, S.N. Dmitirev, V.A. Gorshkov, S. Hübener, V.Ya. Lebedev, O.N. Malyshev, Yu.Ts. Oganessian, A.G. Popeko, E.A. Sokol, S.N. Timokhin, A. Türler, V.M. Vasko, A.V. Yeremin, I. Zvara First Attempt to Chemically Identify Element 112 Radiochim. Acta 11/12, in press (2001).

S U R F A C E C H E M I S T R Y M. A m m a n r i

Using 13N as tracer in heterogeneous atmospheric chemistry experiments Radiochim. Acta 11/12, in press (2001).

M. Ammann, F. Arens, L. Gutzwiller, M. Wachsmuth, H.W. Gäggeler Kinetic study of the HNO¡ sea salt reaction in an aerosol flow reactor J. Aerosol Sei. 32, S247 (2001).

F. Arens, L. Gutzwiller, U. Baltensperger, H.W. Gäggeler, M. Ammann Heterogeneous reaction ofN02 on diesel soot particles Environmental Science & Technology 35 (11), 2191 (2001).

J. Kleffmann, J. Heland, R. Kurtenbach, J.C. Lörzer, P. Wiesen, M. Ammann, L. Gutzwiller, M. Rodenas Garcie, M. Pons, K. Wirth, V. Scheer, R. Vogt HONO Emissions from a Diesel Engine Proceedings of the 94th Annual Conference and Exhibition of the Journal of the Air & Waste Management Association, paper 239 (2001).

A N A L Y T I C A L C H E M I S T R Y A. Eichler, M. Schwikowski, H.W. Gäggeler Meltwater-induced relocation of chemical species in Alpine firn TellusB53, 192 (2001).

S.H. Ehrman, M. Schwikowski, U. Baltensperger, H.W. Gäggeler Sampling and analysis of ice crystals as a function of size Atmos. Environ. 35, 5371 (2001).

E. Gerasopoulos, P. Zanis, A. Stohl, C.S. Zerefos, C. Papastefanou, W. Ringer, L. Tobler, S. Hübener, H.W. Gäggeler, H.J. Kanter, L. Tositti, S. Sandrini A climatology of7Be at four high-altitude stations at the Alps and the Northern Apennines Atmos. Environ. 35, 6347 (2001).

P. Ginot, Ch. Kull, M. Schwikowski, U. Schotterer, H.W. Gäggeler Effects of postdepositional processes on snow composition of a subtropical glacier ( Cerro Tapado, Chilean Andes) J. Geophys. Res. 106, 32375 (2001).

2 0 2

S. Henning, E. Weingartner, S. Schmidt, M. Wendisch, H.W. Gäggeler, U. Baltensperger Size-dependent aerosol activation at the high-alpine site Jungfraujoch (3580 m asi) Tellus 53 B, in press (2001).

T. Huber, M. Schwikowski, H.W. Gäggeler Continuous melting and ion chromatographic analysis of ice cores J . Chromatogr. A. 920/1-2, 193 (2001).

M A . Pouchon, E. Curtí, C. Degueldre, L. Tobler The influence of carbonate complexes on the solubility ofzirconia: new experimental data Prog. Nucl. Energy 38, 443 (2001).

C. Schnabel, J.M. Lopez-Gutierrez, S. Szidat, M. Sprenger, H. Wernli, J . Beer, H.-A. Synal On the origin of129I in rain water near Zürich Radiochim. Acta 11/12, in press (2001).

W. Stichler, U. Schotterer, K. Fröhlich, P. Ginot, C. Kuli, H.W. Gäggeler, B. Pouyaud The influence of sublimation on stable isotopes records from high altitude glaciers in the tropical Andes J . Geophys. Res. 106, 22613 (2001).

E.J. Szondi, E.M. Zsolnay, F. Hegedüs, L. Tobler SPALLDOS: New neutron metrology cross-section library for use at spallation neutron sources in Reactor Dosimetry, Radiation Metrology and Assessment, eds. J.G. Wilhams et al., American Society for Testing and Materials, A S T M S T P 1398,401 (2001).

P R O J E C T R A D W A S T E

D. de F. Dos Santos, M. Argentini, R. Weinreich, H.-J. Hansen Current status of selenium coupling to Hoechst-Carborane Frontiers in Neutron Capture Therapy, eds. F.W. Hawthorne et al., New York, 819 (2001).

203

LABORATORY FOR ION BEAM PHYSICS

G. Bond, B. Kromer, J. Beer, R. Muscheler, M. N. Evans, W. Showers, S. Hoffmann, R. Lotti-Bond, I. Hajdas, G. Bonani Persistent solar influence on North Atlantic climate during the Holocene Science 294, 2130 (2001).

W.S. Broecker, J. Lynch-Stieglitz, E. Clark, I. Hajdas, G. Bonani What caused the atmosphere's C02 content to rise during the last 8000 years? Geochemistry Geophysics Geosystems 2, U1-U13 (2001).

C. Degueldre, M. Pouchon, M. Döbeli, K.Sickafus, K. Hojou, G. Ledergerber, S. Abolhassani-Dadras Behaviour of implanted xenon in yttria stabilized zirconia as inert matrix of a nuclear fuel J. Nucl. Mat.. 289, 115 (2001).

M. Dülk, M. Döbeli, H. Melchior Fabrication of saturable absorbers in InGaAsP/InP bulk semiconductor laser diodes by heavy ion implantation IEEE Journal of Selected Topics in Quantum Electronics 7, 124 (2001).

A. Hessler-Wyser, A. Cuenat, M. Döbeli, C. Abromeit, R. Gotthardt Multilayered phase formation after high-fluence implantation of nickel into aluminium Phil. Mag. Lett. 8 1 , 893 (2001).

S. Ivy-Ochs, R. Wüst, P. W. Kubik, H. Müller-Beck, C. Schlüchter Can we use cosmogenic isotopes to date stone artifacts? Radiocarbon 43, 759 (2001).

D. M. Livingstone, I. Hajdas Climatically relevant periodicities in the thicknesses of biogenic carbonate varves in Soppensee, Switzerland, 9740-6870 calendar yr BP

J. Paleolimnology 25, 17 (2001).

I. Leya, R. Wieler, K. Aggrey, G. F. Herzog, C. Schnabel, K. Metzler, A. R. Hildebrand, M. Bouchard, A.J.T. Jull, H. R. Andrews, M.-S. Wang, T. Ferko, M. E. Lipschutz, S. Neumann, R. Michel Exposure History of the St-Robert (H5) Fall Meteroritics and Planetary Science 36,1479 (2001).

J.M. Lopez-Gutierrez, M. Garcia-Leon, Ch. Schnabel, M. Suter, H.-A. Synal, S. Szidat Wet and dry deposition of129I in Seville (Spain) measured by accelerator mass spectrometry J. Environmental Radioactivity 55, 269 (2001).

F. Marcantonio, R. F. Anderson, S. Higgins, M. Stute, P. Schlosser, P. W. Kubik Sediment focusing in the central equatorial Pacific Ocean Paleoceanography 16, 260 (2001).

K. Matsumoto, W.S. Broecker, E. Clark, D. C. McCorkle, W. R. Martin, I. Hajdas Can deep-ocean carbonate preservation history inferred from atmospheric pC02 account for C-14 and %CaCOj profiles on the Ontong-Java Plateau? Earth and Planet. Sei. Lett. 192, 319 (2001).

M. Pouchon, C. Degueldre, M. Döbeli, Enhanced retention of cesium in yttria stabilised zirconia by co-implantation of iodine Prog. Nuc. Energy 38, 275 (2001).

M. Schaller, F. v. Blankenburg, N. Hovius, P. W. Kubik Large-scale erosion rates from in situ-produced cosmogenic nuclides in European river sediments Earth and Planet. Sei. Lett. 188,441 (2001).

C. Schlüchter, J. Schäfer, S. Ivy-Ochs, S. Tschudi, P. W. Kubik, P. Oberholzer, R. Wieler Alter und Stabilität antarktischer Landschaften in: Die Polarforschung als Schlüssel zum Verständnis der globalen Veränderungen, ed. R. Haudenschild, Schweiz. Kommission für Polarforschung SKP, Bern, 39 (2001).

204

C. Schnabel, J. M. Lopez-Gutierrez, S. Szidat, M. Sprenger, H. Wernli, J. Beer, H.-A. Synal 129I in rain water near Zürich and discussion of its origin Radiochimica Acta 89, 815 (2001).

E. Strouhal, G. Bonani, W. Wölfli Chronometrie Data In: The Tomb of Maya and Merit II, Objects and Skeletal Remains,

ed. Maarten J. Raven, National Museum of Antiquities Leiden / Egypt Exploration Society, 98 (2001).

S. Tschudi, S. Ivy-Ochs, C. Schliichter, P. W. Kubik, H. Rainio New absolute dating of the Yonger Dryas Salpasselkä I formation with cosmogenic 26Al Geology 53,131 (2001). G. Wagner, G., J. Beer, J. Masarik, R. Muscheler, P.W. Kubik, W. Mende, C. Laj, G.M. Raisbeck, F. Yiou Presence of the solar de Vries cycle (-205 years) during the last ice age Geophys. Res. Lett. 28(2), 303 (2001).

G. Wagner, C. Laj, J. Beer, C. Kissel, R. Muscheler, J. Masarik, H.-A. Synal Reconstruction of the paleoaccumulation rate of central Greenland during the last 75 kyr using the cosmogenic radionuclides 36CI and 10Be and geomagnetic field intensity data Earth and Planet. Sei. Lett. 193, 515 (2001).

205

CONTRIBUTIONS TO CONFERENCES AND WORKSHOPS

LABORATORY FOR PARTICLE PHYSICS

D. Anagnostopoulos, M. Augsburger, G. Borchert, D. Chatellard, P. El-Khoury, J.-P. Egger, D. Gotta, P. Hauser, M. Hennebach, P. Indelicato, K. Kirch, S. Lenz, Y.-W. Liu, B. Manil, N. Nelms, Th. Siems, and L. M. Simons - R-98-01 Collaboration Charged pion mass determination and energy-calibration standards based on pionic X-ray transitions Proc. of Hydrogen Atom II: Precise physics of simple atomic systems (PSAS 2000), Castiglione della Pescaia (Italy), June 1-3, 2000, eds. S. G. Karshenboim, F. S. Savone, G. F. Bassani, M. Inguscio, and T. W. Hansen, Springer Verlag, Berlin, 500 (2001).

D. Anagnostopoulos, S. Biri, G. Borchert, W. H. Breunlich, M. Cargnelli, J.-P. Egger, B. Gartner, D. Gotta, P. Hauser, M. Hennebach, P. Indelicato, T. Jensen, R. King, F. Kottmann, B. Lauss, Y.-W. Liu, V. E. Markushin, J. Marton, N. Nelms, G. C. Oades, G. Rasche, P. A. Schmelzbach, L. M. Simons and J. Zmeskal - R-98-01 Collaboration Pionic Hydrogen: Status and Outlook Proc. of Hydrogen Atom II: Precise physics of simple atomic systems (PSAS 2000), Casiglione della Pescaia (Italy), June 1-3 2000, eds. S. G. Karshenboim, F. S. Savone, G. F. Bassani, M. Inguscio, and T. W. Hansen, Springer Verlag, Berlin, 508 (2001).

D. Banas, M. Berset, D. Chmielewska, M. Czarnota, J.-Cl. Dousse, J. Hoszowska, Y.-P. Maillard, O. Mauron, T. Mukoyama, M. Pajek, M. Polasik, P. A. Raboud, J. Rzadkiewicz and Z. Sujkowski - Z01-03 Collaboration High-resolution study ofL- and M-x-ray satellites excited in collisions of360-MeVoxygen ions with heavy atoms XII International Conference on Photonic, Electronic and Atomic Collisions ICPEAC 2001, Santa Fe (USA), 2001.

M. Beck, K. Bodek, A. Czarnecki, W. Fetscher, W. Haeberli, C. Hilbes, K. Kirch, St. Kistryn, A. Kozela, J. Pulut, P. Schuurmans, A. Serebrov, N. Severijns, J. Sromicki, E. Stefan and J. Zejma, Search for Time Reversal Violating Effects in the Decay of Free Neutrons International Nuclear Physics Conference, Berkeley, California (USA), July 30 - August 3, 2001.

W. Bertl.eí al., - R87-03 - SINDRUM 2 Collaboration Search for Muon - Electron Conversion on Gold International Europhysics Conference on High-Energy Physics (HEP 2001), Budapest (Hungary), July 12 - 18,2001, Proceedings prHEP-hep2001/155; http://jhep.sissa.it.

F. Birabenei al., F. Kottmann, V. E. Markushin, R. Pohl, L. M. Simons, D. Taqqu, - R-98-03 Collaboration Towards a Lamb shift measurement in muonic hydrogen AIP Conf. Proc. 564,13 (2001).

Ch. Buehler, U. Greuter, G. Frey, O. Zaharko, M. Koennecke, J. Schefer, P. Rasmussen, D. Schaniel, D. Clemens, A. Gabriel, J. Felsche and N. Schlumpf, Sub-Nanosecond Multi-Channel Time-to-Digital Converter for the 2-D Position Sensitive Neutron Detectors at TriCS and AMOR International Conference on Neutron Scattering (ICNS 2001),TU-München (Germany), Sept. 9 - 13, 2001, Appl. Phys. A 73,suppl., S315 (2001).

Ch. Buehler, K. Kim, C. Y Dong, B. R. Masters, M. Auer and P. T. C. So (invited talk), New Frontiers in Biomedical Imaging 7th Conference on Methods and Applications of Fluorecence Spectroscopy, Amsterdam (NL), September 16 - 19, 2001.

Ch. Buehler, K. Kim, U. Greuter, N. Schlumpf, C. Y Dong and P. T. C. So (invited talk), High-Speed Multi-Photon Imaging Max-Plank-Institute for Biophysical Chemistry, Goettingen (Germany), 1st October 2001.

M. Daum - UCN Collaboration (PSI-PNPI-CRACOW-ILL) An Ultracold Neutron Facility at PSI Tagung der Schweizerischen Physikalischen Gesellschaft, Duebendorf (CH), March 3 - 4 , 2001.

206

M. Daum - UCN Collaboration (PSI-PNPI-CPvACOW-ILL) An Ultracold Neutron Facility at PSI Tagung der Deutschen Physikalischen Gesellschaft, Bonn (Germany), March 26 - 27, 2001.

M. Daum - UCN Collaboration (PSI-PNPI-CRACOW-ILL) An Ultracold Neutron Facility at PSI The 3rd UCN workshop, Pushkin (RU), June 1 8 - 2 2 , 2001.

M. Daum, - N T O F collaboration (PSI-ETHZ-Beijing) Experimentaal verification of Coulomb deexcitation in pionic hydrogen Pion Nucleón Workshop Villigen (CH), November 26 - 27,2001.

M. Daum - UCN Collaboration (PSI-PNPI-CRACOW-ILL) An Ultracold Neutron Facility at PSI UCN workshop, Villigen (CH), December 3 - 4, 2001.

J.-Cl. Dousse, D. Bañas, D. Castella, D. Chmielewska, D. Corminboeuf, I. Fijal, J. Hoszowska, M. Jaskola, A. Korman, T. Ludziejewski, Y.-P. Maillard, O. Mauron, M. Pajek, M. Polasik, P.-A. Raboud, J. Rzadkiewicz, and Z. Sujkowski - Z-01-03 Collaboration High-resolution study of thorium and uranium L x-ray spectra induced by impact with fast oxygen ions 7th EPS Conf. on At. Mol. Phys., Berlin (Germany), 2001), Europhys. Conf. Abs tr. 25 B, 47 (2001).

W. Fetscher, Measurement of the polarization vector of the e+ from the decay of polarized p+ as a test of time reversal invariance EDM 2001 Workshop, Brookhaven, NY (USA).

D. Gotta (invited talk), The pionic hydrogen experiment at PSI International RIKEN Conference on Muon Catalyzed Fusion and Related Exotic Atoms, Shimoda (Japan), April 22-26,2001.

D. Gotta, The new pionic hydrogen experiment at PSI 9th International Symposium on Meson-Nucleon Physics and the Structure of the Nucleón, Washington, DC (USA), July 26-31,2001.

D. Gotta (invited talk), First results from the new pionic hydrogen experiment Workshop on Molecular Effects in the Exotic Hydrogen Cascade, PSI, Villigen (CH), November 26-27, 2001.

U. Greuter, Ch. Buehler, P. Rasmussen, M. Emmenegger, D. Maden, M. Koennecke and N. Schlumpf Concept and Realisation of a Fully Configurable and Programmable Data Acquisition System for the Neutron Scattering Instruments at SINQ International Conference on Neutron Scattering (ICNS 2001),TU-Munchen (Germany), Sept. 9 - 13, 2001, Appl. Phys. A 73,suppl., S319 (2001).

M. Hennebach, Towards a new high-precision determination of the pion-nucleon scattering length

Frühjahrstagung der Deutschen Physikalischen Gesellschaft DPG, Erlangen (Germany), March 19 - 22, 2001.

M. Hennebach, The pionic hydrogen experiment at PSI

Indian SummerSchool on the Structure of Hadrons, Prag (CZ), July 9 - 13, 2001.

M. Hennebach, The new pionic hydrogen experiment at PSI

2nd Int. Workshop on Hadronic Atoms, Bern (CH), October 1 1 - 12, 2001.

R. Henneck, Ultrakalte Neutronen am PSI und das neue Experiment zur Messung des elektrischen Dipolmomentes (EDM) des Neutrons Seminarvortrag Univ. Heidelberg (Germany), November 7, 2001.

207

R. Henneck, Ultrakalte Neutronen am PSI und das neue Experiment zur Messung des elektrischen Dipolmomentes (EDM) des Neutrons Seminarvortrag Univ. Stuttgart (Germany), November 8, 2001.

R. Henneck, Test experiment to measure the magnetic shielding and the stabilization of resonance conditions in an EDM spectrometer UCN workshop, Villigen (CH), December 3 - 4, 2001.

R. Henneck, Development of a large vessel with long UCN storage time UCN workshop, Villigen (CH), December 3 - 4, 2001.

R. Henneck, Ultrakalte Neutronen am PSI und das neue Experiment zur Messung des elektrischen Dipolmomentes (EDM) des Neutrons Seminarvortrag Univ. Tuebingen (Germany), December 7, 2001.

P. Indelicato and L. M. Simons - R-98-01 Collaboration Crystal Spectroscopy and Exotic Atoms QED 2000, 2nd Workshop on Quantum Electrodynamics and Physics of the Vacuum, Trieste (Italy), October 5-11, 2000, ed. G. Cantatore, AIP Conference Proceedings 564,264 (2001).

Q. Ingram et al, Z. Antunovic et al., Avalanche Photodiodes for the CMS Electromagnetic Calorimeter International Europhy sics Conference on High-Energy Phy (HEP 2001), Budapest (Hungary), July 12 - 18, 2001; prHEP-hep2001/156.

P.-R. Kettle - MuEgamma Collaboration Search for the Lepton-Flavour Violating (LFV) Decay p —> e + 7 Annual Meeting of Swiss Physical Society SPS, Dübendorf (CH), May 2-3,2001.

P.-R. Kettle - NewHeavns Collaboration The KARMEN Time Anomaly: Search for a Neutral Particle of Mass 33.9 MeV in Pion Decay Proceedings of the XXXth International Conference on High Energy Physics, Osaka (Japan), 27th July to 2nd August 2000; eds C. S. Lim and Taku Yamanaka, p. 1177.

K. Kirch - UCN Collaboration (PSI-PNPI-CRACOW-ILL) Comparison of spallation UCN source concepts The 3rd UCN workshop, Pushkin (RU), June 1 8 - 2 2 , 2001.

K. Kirch - UCN Collaboration (PSI-PNPI-CRACOW-ILL) An Ultracold Neutron Facility at PSI International Nuclear Physics Conference, Berkeley (USA), August 2001.

K. Kirch - UCN Collaboration (PSI-PNPI-CRACOW-ILL) Studies of solid deuterium UCN workshop, Villigen (CH), December 3 - 4 , 2001.

B. Kotlinski - E94-09 - CMS Collaboration Higher level trigger based on pixels in CMS

10th International Workshop on Vertex Detectors VERTEX2001, Brunnen (Switzerland), September 24-28,2001.

F. Kottmann, Cyclotron trap and slow muon beams

International Workshop on Radioactive Antiprotonic and Muonic Atoms, CERN (CH), February 23, 2001.

F. Kottmann, Low energy muon cooling and extraction from a magnetic trap 37th Meeting of the Neutrino Factory Working Group, CERN (CH), March 28, 2001. F. Kottmann, The muonic hydrogen Lamb shift experiment at PSI International RIKEN Conference on Muon Catalyzed Fusion and Related Exotic Atoms, (muCFOl), Shimoda (Japan), April 22 - 26, 2001.

208

R. Pohl, First observation of long-lived ßp(2S) atoms International RIKEN Conference on Muon Catalyzed Fusion and Related Exotic Atoms, (muCFOl), Shimoda (Japan), April 22 - 26,2001.

R. Pohl, Lamb shift in muonic hydrogen and the proton charge radius

Ringberg Seminar of the Max Planck Institute of Quantum Optics, Schloss Ringberg (Germany), September 24 - 28, 2001.

R. Pohl, The Lamb shift in muonic hydrogen and the proton charge radius Seminar über Kern - und Teilchenphysik, ETH Zurich (CH), October 30, 2001.

R. Pohl, Measurement of the kinetic energies of ¡j,p(Is) and determination of the ßp(2s) lifetime International Workshop on Molecular Effects in the Exotic Hydrogen Cascade, PSI (CH), November 26 - 27, 2001.

P. Rasmussen, J. Kohlbrecher, J. Egger, J. Mesot, M. Schild, R. Baetscher, E. Berruyer, and N. Schlumpf Concept and Realisation of2D and ID Detector Readout Systems with new Adjustment and Calibration Features International Conference on Neutron Scattering (ICNS 2001),TU-Munchen (Germany), Sept. 9 - 13, 2001, Appl. Phys. A 73,suppl., S85 (2001).

T. Rohe -E94-09 - CMS Collaboration Sensor development for the CMS pixel detector 5th International Conference on Large Scale Applications and Radiation Hardness of Semiconductor Detectors, Firenze (Italy), July 4-6,2001.

T. Rohe -E94-09 - CMS Collaboration The CMS Pixel Detector 7th Conference on Advanced Technology and Particle Physics, Como (Italy), October 15-17,2001.

A. Serebrov - UCN Collaboration (PSI-PNPI-CRACOW-ILL) A new spectrometer to measure the neutron electric dipole moment Tagung der Schweizerischen Physikalischen Gesellschaft, Duebendorf (CH), March 3 - 4 , 2001.

A. Serebrov - UCN Collaboration (PSI-PNPI-CRACOW-ILL) A new spectrometer to measure the neutron electric dipole moment UCN workshop, Villigen (CH), December 3 - 4, 2001.

D. Taqqu, The experimental study of cascade molecular transitions

International Workshop on Molecular Effects in the Exotic Hydrogen Cascade, PSI (CH), November 26 - 27, 2001.

P. Truöl et al, J. Egger, W. D. Herold, H. Kaspar, A new measurement ofK^4 decay and the s—wave -kit— scattering length - E865 Collaboration International Europhysics Conference on High-Energy Physics (HEP 2001), Budapest (Hungary), July 12 - 18,2001; prHEP-hep2001/175. THEORY GROUP American Linear Collider Working Group T. Abe et al., A. Denner, Linear collider physics resource book for Snowmass 2001 Resource Book APS / DPF / DPB Summer Study on the "Future of Particle Physics" (Snowmass 2001), Snowmass (USA), June 30 - July 21, 2001; hep-ex/0106058.

E. Accomando, CP violating MSSM: what consequences for the Higgs search? To appear in the Proceedings of the 13th Meeting on "LEP2 physics" (LEPTRE 2001), Rome (Italy), April 18-20,2001.

209

E. Accomando, Energy scales and non-annihilation processes To appear in the Proceedings of the 13th Meeting on "LEP2 physics" (LEPTRE 2001), Rome (Italy), April 18-20,2001.

ECFA/DESY LC Physics Working Group J. A. Aguilar-Saavedra et al., A. Denner, M. Spira, TESLA: the superconducting electron positron linear collider with an integrated X-ray laser laboratory. Technical design report, Part 3, Physics at ane+e~ collider; hep-ph/0106315.

ECFA/DESY Photon Collider Working Group B. Badeleke/ al., M. Spira, TESLA: the superconducting electron positron linear collider with an integrated X-ray laser laboratory. Technical design report, Part 6, Physics at an e+e~ collider, hep-ex/0108012.

U. Baure/ al., A. Denner, Status and prospects of theoretical predictions for weak gauge boson production processes at lepton and hadron colliders To appear in the Proceedings of APS / DPF / DPB Summer Study on the "Future of Particle Physics" (Snowmass 2001), Snowmass (USA), June 30 - July 21,2001 ; hep-ph/0111060.

A. Denner (invited talk), Präzisionstests der Elektroschwachen Wechselwirkung an Collidern Physikalisches Kolloquium, University Bielefeld (Germany), January 22, 2001.

A. Denner (invited talk), Leading Electroweak Corrections at High Energies Graduiertenseminar, University Leipzig (Germany), June 26, 2001.

A. Denner (invited talk), Präzisionstests der Elektroschwachen Wechselwirkung an Collidern Physikalisches Kolloquium, University Wuppertal (Germany), June 28, 2001.

A. Denner et al. (invited talk), Precise predictions for e+e~ —> 4f(+j) with anomalous couplings International Europhysics Conference on "High-Energy Physics" (HEP 2001), Budapest (Hungary), July 12 - 18,2001; hep-ph/0110402.

A. Denner (invited talk), Electroweak radiative corrections at high energies International Europhysics Conference on "High-Energy Physics" (HEP 2001), Budapest (Hungary), July 12 - 18,2001; hep-ph/0110155.

A. Denner (invited talk), Leading Electroweak Corrections at High Energies Theorieseminar at University Heidelberg (Germany), July 26, 2001.

S. Dittmaier, P. M. Zerwas, M. Krämer and M. Spira, Higgs radiation off quarks in the Standard Model and supersymmetric theories at e+e~ colliders LC-TH-2001-069,2001,in: "2nd ECFA/DESY Study 1998-2001", 2460.

S. Dürr The phase transition in the multiflavour Schwinger model Proceedings of the International Conference "Quantization, Gauge Theory and Strings", dedicated to the memory of Professor Efim Fradkin, Moscow (Russia), June 5 - 10, 2000, eds. A. Semikhatov et ai, Scientific World, Moscow (2001).

S. Dürr Simple check of the vacuum structure in full QCD lattice simulations Proceedings of the QCD conference in Martina Franca (Italy), June 20 - 24, 2001 ; hep-lat/0108015.

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S. Dürr Testing the Leutwyler-Smilga prediction regarding the global topological charge distribution on the lattice Proceedings of the 8th Euroconference on "Quantum Chromodynamics", Montpellier (France), July 6 - 12,2000, ed. S. Narison Nucl. Phys. Proc. Suppl. 96, 287 (2001).

S. Dürr Study of the Leutwyler-Smilga regimes: lessons for full QCD simulations Proceedings of the XVIII International Symposion on "Lattice Field Theory", Bangalore (India), August 17 - 22,2000, eds. A. Patel etat, Nucl. Phys. Proc. Suppl. 94,506 (2001).

S. Dürr Topology and pion correlators - a study in the Nf = 2 Schwinger model To appear in the Proceedings of the XIX International Symposion on "Lattice Field Theory", Berlin (Germany), August 19 - 24, 2001.

T. S. Jensen and V. E. Markushin, Atomic cascade in hadronic atoms 9th Int. Symp. on "Meson-Nucleon Physics and the Structure of the Nucleón" (Menu2001), Washington DC (USA), July 26-31,2001.

T. S. Jensen and V. E. Markushin, Stark mixing and elastic scattering in pionic and muonic hydrogen Proceedings of the 17th European Conference on "Few-Body Problems in Physics", Evora (Portugal), September 11 - 16, 2000. Nucl. Phys. A 689,537c (2001).

T. S. Jensen and V. E. Markushin, Atomic cascade in hadronic atoms 2nd Workshop on "Hadronic Atoms" (HadAtomOl), Bern (Switzerland), October 1 1 - 12,2001.

T. S. Jensen and V. E. Markushin, Atomic cascade in light exotic atoms Workshop on "Molecular Effects in the Exotic Hydrogen Cascade", PSI (Switzerland), November 26-27,2001.

V. A. Kuz'min, T. V. Tetereva and K. Junker, On the strength of spin-isospin transitions in A = 28 nuclei BLTP International Conference on "Nuclear Structure and Related Topics" (NSRT 2000), Dubna (Russia), June 6-10, 2000, Phys. Atom. Nucl. 64,1169 (2001).

V. E. Markushin and T. S. Jensen, Atomic cascade and X-ray yields in light exotic atoms Proceedings of the 7th International Conference on "Hypernuclear and Strange Particle Physics" (HYP 2000), Torino (Italy), October 23 - 27, 2000. Nucl. Phys. A 691, 318c (2001).

V. E. Markushin (invited talk), The Scalar Mesons that Are Not Like Others Inst. f. Strahlen u. Kernphysik (ISKP), Univ. Bonn (Germany), February 8, 2001.

V. E. Markushin (invited talk), Kinetics of atomic cascade in light exotic atoms International RIKEN Conference on "Muon Catalyzed Fusion and Related Exotic Atoms" (/xCF-01), Shimoda (Japan), April 22-26, 2001.

V. E. Markushin (invited talk), Scattering of light exotic atoms in excited states International RIKEN Conference on "Muon Catalyzed Fusion and Related Exotic Atoms" (/xCF-01), Shimoda (Japan), April 22-26,2001.

211

V. E. Markushin (invited talk), Bose-Einstein Correlations in Nucleon-Antinucleon Annihilation at Rest ETH, Zürich (Switzerland), June 12, 2001.

V. E. Markushin (invited talk), Light Exotic Atoms Aktuelles aus der Teilchenphysik, Univ. Zürich (Switzerland), June 27,2001.

M. Melles (invited talk), Electroweak Sudakov Corrections Michigan State University (USA), March 12, 2001.

M. Melles (invited talk), Electroweak Sudakov Corrections University of Michigan (USA), March 13, 2001.

M. Melles (invited talk), Heavy Quark Background and the Precision of the Two Photon Partial Width at the Compton Collider International Workshop on High Energy gamma gamma Colliders at Fermilab, Chicago (USA), March 14, 2001.

M. Melles, Precision Higgs Physics at a 7 7 collider International Workshop on "High-Energy Photon Colliders" (GG 2000), Hamburg (Germany), June 14-17, 2000, Nucl. Instrum. Meth. A 472,128 (2001).

M. Melles, Two loop mass effects in the static position space QCD potential Proceedings of the 8th Euroconference on "Quantum Chromodynamics", Montpellier (France), July 6 -12, 2000, ed. S. Narison Nucl. Phys. Proc. Suppl. 96, 472 (2001).

M. Melles ( invited talk), Electroweak Sudakov Corrections

Intern. Linear Collider Workshop at Fermilab, Chicago (USA), Oct. 26, 2001.

Michael Melles, Higgs Mechanismus und Phänomenologie Habilitationsvortrag, Universität Zürich, December 16, 2001.

R. Rosenfelder (invited talk), Proton Charge Radius from ep-Scattering

Workshop on "Hadron Form Factors", Physikzentrum Bad Honnef (Germany), April 17 -19, 2001.

M. Spira (invited talk), SUSY Particle Production at Hadron Colliders QCDNET-YR Meeting, ETH Zürich (Switzerland), February 19, 2001.

M. Spira (invited talk), Status Report of the Higgs Working Group (Convenor) Workshop "Physics at TeV Colliders", Les Houches (France), May 22 - June 1, 2001.

M. Spira (invited talk), ttH Production at Hadron Colliders

Workshop "Physics at TeV Colliders", Les Houches (France), May 22 - June 1, 2001.

M. Spira (invited talk), SUSY Particle Production at Hadron Colliders Workshop "Physics at TeV Colliders", Les Houches (France), May 22 - June 1, 2001.

212

M. Spira (invited talk), Summary Report of the Higgs Working Group (Convenor)

Workshop "Physics at TeV Colliders", Les Houches (France), May 22 - June 1, 2001.

M. Spira (invited talk), Theory Challenges for Higgs and SUSY at Colliders

Workshop "Euro-GDR SUPERSYMMETRY, 1st Reunion", Aachen (Germany), June 6, 2001.

M. Spira (invited talk), New Results on Higgs and SUSY Particle Production at Hadron Colliders

Workshop "Theory Institute 2001: From Supersymmetry To Extra Dimensions", Argonne (USA), June 21, 2001.

M. Spira (invited talk), New Results on Higgs and SUSY Particle Production at Hadron Colliders Seminar at Fermilab, Batavia (USA), June 22, 2001. M. Spira (invited talk), Higgs and SUSY Particle Production at Hadron Colliders: QCD Corrections Seminar at University of Barcelona (Spain), October 22, 2001. M. Spira, Higgs radiation off quarks in the Standard Model and supersymmetric theories at e+e~ colliders 5th International Symposium on "Radiative Corrections (RADCOR 2000): Applications of Quantum Field Theory to Phenomenology", Carmel, California (USA), September 11-15, 2000; hep-ph/0101314.

LABORATORY FOR ASTROPHYSICS

B. Allongue, G. Berger, F. Faccio, W. Hajdas, C. Rivetta, Single event burnout in DC-DC converters for the LHC experiment 6th European Conference on radiation and its effects on components and systems (RADECS), Grenoble (France), September 10 - 14, 2001

K. Arzner, M. Scholer, R. Treumann (talk and poster), On a collisonless Dreicer field CESRA Workshop on Energy Conversion and Particle Acceleration in the Solar Corona, Ringberg (Germany), July 2 - 6, 2001.

M. Audard (invited review), First results from X-ray Spectroscopy of Stellar Coronae with XMM-Newton RGS Royal Astronomical Society Discussion Meeting on Coronal Heating in the Sun and Late-Type Stars, London (United Kingdom), January 12, 2001.

M. Audard, M. Güdel, A. Sres, R. Mewe, A. J. J. Raassen, E. Behar, C. R. Foley, R. L. J. van der Meer, A Study of the Coronal Plasma in RS CVn Binary Systems: HR 1099 and co 3 5 t h ESLAB Symposium : "Stellar Coronae in the Chandra and XMM-Newton Era", Noordwijk (Netherlands), June 25 - 29, 2001.

M. Audard, M. Güdel, A. Sres, R. Mewe, A. J. J. Raassen, E. Behar, C. R. Foley, R. L. J. van der Meer, A Study of the Coronal Plasma in RS CVn Binary Systems: HR 1099 and co The 12th Workshop on Cool Stars, Stellar Systems and the Sun, Boulder (USA), July 30 - August 3, 2001.

M. Audard, M. Güdel, A. Sres, R. Mewe, A. J. J. Raassen, R. L. J. van der Meer, E. Behar, C. R. Foley, The Chandra LETG and XMM-Newton Spectra of HR 1099

"Two Years of Science with Chandra", Washington DC (USA), September 5 - 7, 2001.

M. Audard, XMM-Newton X-ray Spectroscopy of Stellar Coronae Annual Assembly of the Swiss Society for Astrophysics and Astronomy, Yverdon (CH), October 18, 2001.

213

M. Audard, M. Güdel, A. Sres, R. Mewe, A. J. J. Raassen, R. L. J. van der Meer, E. Behar, C. R. Foley, The Chandra LETG and XMM-Newton Spectra of HR 1099

"New Visions of the X-ray Universe in the XMM-Newton and Chandra Era", Noordwijk (Netherlands), November 26 - 30,2001.

M. Audard, M. Güdel, Elemental Abundances in Stellar Coronae with XMM-Newton

"New Visions of the X-ray Universe in the XMM-Newton and Chandra Era", Noordwijk (Netherlands), November 26 - 30,2001.

M. Audard (invited talk), Reducing Reflection Grating Spectrometer Data for Point-like Sources "New Visions of the X-ray Universe in the XMM-Newton and Chandra Era", Noordwijk (Netherlands), November 26 - 30,2001. T. R. Ayres, A. Brown, S. A. Drake, A. K. Dupree, M. Güdel, E. Guiñan, G. M. Harper, C. Jordan, J. L. Linsky, D. Reimers, J. H. M. M. Schmitt, T. Simon, Origins, Structure, and Evolution of Magnetic Activity in the Cool Half of the H-R Diagram: Progress Report on a Major HST STIS Stellar Survey 197th Meeting of the AAS, San Diego (USA), January 2001, Bull. Am. Astron. Soc. 197,44.07.

J. M. DePasquale, J. J. Bochanski, E. F. Guiñan, I. Ribas, G. P. McCook, J. D. Dorren, M. Güdel, When the Sun was Young: A Multi-Frequency Study of the Young Solar Analog HD 129333 ( = EKDra) 198th Meeting of the AAS, Pasadena (USA), June 2001. Bull. Am. Astron. Soc. 198,44.04.

S. A. Drake, L. Brenneman, N. E. White, T. Simon, K. P. Singh, M. Güdel, M. Audard, The Quiescent Corona ofUXAri as seen by Chandra The 12th Workshop on Cool Stars, Stellar Systems and the Sun, Boulder (USA), July 30 - August 3, 2001.

T. Dumm, M. Güdel, W. Schmutz, M. Audard, H-R. Schild, M. Leutenegger, K. van der Hucht, XMM Observations of the WR+O System Gamma Velorum "New Visions of the X-ray Universe in the XMM-Newton and Chandra Era", Noordwijk (Netherlands), November 26 - 30,2001.

M. Fivian, Der HESSI Satellit Seminar: Institut für theoretische Physik, Universität Zürich (CH), January 24, 2001.

E. J. Gaidos, G. Gonzales, M. Güdel, S. R. Heap, G. Henry, Observations of Nearby Solar Analogs "Young Stars Near Earth": Progress and Prospects. Mountain View CA (USA), March 28 - 30, 2001.

M. Güdel (invited review), X-Ray Spectroscopy of Stars Royal Astronomical Society Expert Discussion Meeeting, London (UK), February 9, 2001.

M. Güdel, (invited review), Multi-Wavelength Aspects of Coronae 3 5 t h ESLAB Symposium : "Stellar Coronae in the Chandra and XMM-Newton Era", Noordwijk (Netherlands), June 25 - 29, 2001.

M. Güdel, (invited review), X-Ray Emission from Stellar Coronae

"Two Years of Science with Chandra", Washington DC (USA), September 5 - 7, 2001.

M. Güdel, (invited review), New Views and Visions of Stellar Coronae and Stellar Winds

"New Visions of the X-ray Universe in the XMM-Newton and Chandra Era", Noordwijk (Netherlands), November 26 - 30,2001.

M. Güdel, (invited review), Stellar Coronae: Formation, Structure, and Evolution

Annual Assembly of the Swiss Society for Astrophysics and Astronomy, Yverdon (CH), October 18, 2001.

M. Güdel, (invited talk), X-Raysfrom Stars: A New View with XMM-Newton and Chandra Astrophysics Seminar, Observatoire de Genève, Versoix (CH), November 13, 2001.

214

M. Güdel, Stellar Flares Front Smallest to Largest - What Do They Tell Us About Energy Release ? Astrophysics Colloquium, Institute of Astronomy, ETH Zürich (CH), December 18, 2001.

M. Güdel, M. Audard, A. Sres, R. Wehrli, E. Behar, A. J. J. Raassen, H. R. M. Magee, XMM-Newton Probes the Solar Past: Observations of Solar Analogs at Different Ages 3 5 t h ESLAB Symposium : "Stellar Coronae in the Chandra and XMM-Newton Era", Noordwijk (Netherlands), June 25 - 29, 2001.

M. Güdel, M. Audard, V. L. Kashyap, J. J. Drake, E. F. Guiñan, Flares and Coronal Heating in Active Stars - A Statistical Investigation 3 5 t h ESLAB Symposium : "Stellar Coronae in the Chandra and XMM-Newton Era", Noordwijk (Netherlands), June 25 - 29, 2001.

M. Güdel, M. Audard, K. W. Smith, A. Sres, C. Escoda, R. Wehrli, E. F. Guiñan, I. Ribas, A. J. Beasley, R. Mewe, A. J. J. Raassen, E. Behar, H. Magee, A Systematic Spectroscopic X-Ray Study of Stellar Coronae with XMM-Newton The 12th Workshop on Cool Stars, Stellar Systems and the Sun, Boulder (USA), July 30 - August 3, 2001.

M. Güdel, M. Audard, M. Horvath, K. W. Smith, S. L. Skinner, J. L. Linsky, J. J. Drake, A XMM-Newton Study of Próxima Centauri

"New Visions of the X-ray Universe in the XMM-Newton and Chandra Era", Noordwijk (Netherlands), November 26 - 30,2001.

E. F. Guiñan, I. Ribas, L. E. DeWarf, G. Harper, M. Güdel, Evolution of the FUV Sun in Time: FUSE Observations of the Solar Analogs with Different Ages 198th Meeting of the AAS, Pasadena (USA), June 2001. Bull. Am. Astron. Soc. 198,22.01. W. Hajdas Proton Irradiation Facility at PSI 2001 ESA/ESTEC, Noordwijk (NL), January 30 - 31 2001.

J. W. den Herder, A. C. Brinkman, S. M. Kahn, G. Branduardi-Raymont, M. Audard, A. J. den Boggende, J. Cottam, C. Erd, M. Güdel, J. S. Kaastra, F. B. Paerels, J. R. Peterson, A. P. Rasmussen, J. D. Reynolds, T. Tamura, C. P. de Vries (invited talk), Calibration of the Reflection Grating Spectrometers onboard of XMM-Newton "New Visions of the X-ray Universe in the XMM-Newton and Chandra Era", Noordwijk (Netherlands), November 26 - 30,2001.

V. L. Kashyap, J. J. Drake, M. Güdel, M. Audard, Viability of Flare Heating of Stellar Coronae AGU 2001 Spring Meeting, Solar-Planetary Space Physics and Aeronomy, Boston (USA), May 29 - June 2, 2001.

V. L. Kashyap, J. J. Drake, M. Güdel, M. Audard, Flares Heating of Stellar Coronae 3 5 t h ESLAB Symposium : "Stellar Coronae in the Chandra and XMM-Newton Era", Noordwijk (Netherlands), June 25 - 29, 2001.

V. L. Kashyap, J. J. Drake, M. Güdel, M. Audard, Modeling Stellar Microflares

Statistical Challenges in Modern Astronomy III, Pennsylvania State University (USA), July 18 -21 ,2001 .

Ph. Lerch Kryodetektoren und ihre Anwendung in der Astrophysik

Seminar: Institut für theoretische Physik, Universität Zürich (CH), January 31,2001.

G. Paesold, A. O. Benz, K.-L. Klein, N. Vilmer, Spatial Analysis of Solar Type III Events Associated with Narrowband Spikes at Metric Wavelengths

CESRA Workshop on Energy Conversion and Particle Acceleration in the Solar Corona, Ringberg (Germany), July 2 - 6 , 2001.

G. Paesold, A. O. Benz, Testparticle Simulation of the Electron Firehose Instability CESRA Workshop on Energy Conversion and Particle Acceleration in the Solar Corona, Ringberg (Germany), July 2 - 6 , 2001.

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G. Paesold, A. O. Benz, Electron acceleration and plasma instabilities in solar flares Annual Assembly of the Swiss Society for Astrophysics and Astronomy, Yverdon (CH), October 18, 2001.

A. J. J. Raassen, M. Audard, R. Mewe, M. Güdel, R. L. J. van der Meer, E. Behar, Emission Measure Modeling and Abundance Determination ofProcyon by Means of a Variety of Instruments on board of Chandra and XMM-Newton 3 5 t h ESLAB Symposium : "Stellar Coronae in the Chandra and XMM-Newton Era", Noordwijk (Netherlands), June 25 - 29, 2001.

A. J. J. Raassen, J. S. Kaastra, R. L. J. van der Meer, R. Mewe, M. Audard, M. Güdel, J.-U. Ness, E. Behar, Temperature Determination and Emission Measure Modeling of the Coronae of a Centauri and Procyon The 12th Workshop on Cool Stars, Stellar Systems and the Sun, Boulder (USA), July 30 - August 3, 2001.

A. J. J. Raassen, M. Audard, R. Mewe, M. Güdel, J. S. Kaastra, Temperature determination and emission measure modeling of the corona of of ATMic

"New Visions of the X-ray Universe in the XMM-Newton and Chandra Era", Noordwijk (Netherlands), November 26 - 30,2001.

M. Scholer, K. Arzner, Hybrid simulations of magnetotail reconnection: Turbulence in the post plasmoid plasma sheet, Les Wolliscroft Memorial Conference / Sheffield Space Plasma Meeting: Multipoint Measurements versus Theory, Sheffield (UK), April 24 - 26, 2001. K. W. Smith, M. Güdel, M. Audard, R. Jeffries, Pre-main Sequence Dwarfs near Gamma Velorum "New Visions of the X-ray Universe in the XMM-Newton and Chandra Era", Noordwijk (Netherlands), November 26 - 30,2001.

K. W. Smith, M. Güdel, M. Audard, E. Behar, R. Mewe, The Neupert Effect in Sigma Geminorum "New Visions of the X-ray Universe in the XMM-Newton and Chandra Era", Noordwijk (Netherlands), November 26 - 30,2001.

K. W. Smith, M. Güdel, M. Audard, A Menagerie of Stellar Flares "New Visions of the X-ray Universe in the XMM-Newton and Chandra Era", Noordwijk (Netherlands), November 26 - 30,2001.

B. Stelzer, V. Burwitz, R. Neuhäuser, M. Audard, J. H. M. M. Schmitt, The Joint XMM-Newton and Chandra view of YY Gem 3 5 t h ESLAB Symposium : "Stellar Coronae in the Chandra and XMM-Newton Era", Noordwijk (Netherlands), June 25 - 29, 2001.

K. Thomsen Röntgensatelliten, XMM Seminar: Institut fur theoretische Physik, Universität Zürich (CH), January 17, 2001.

A. Zehnder Dark Matter Kernphysik - Kolloquium, ETH - Zürich (CH), November 27, 2001.

LABORATORY FOR MUON SPIN SPECTROSCOPY

A. Amato (invited talk), Critical point(s) and unconventional Superconductivity in UPt^ MuSR Users Meeting, PSI, Villigen (Switzerland), January 25, 2001.

A. Amato (invited talk), Critical point(s) and unconventional Superconductivity in UPt^ Seminar, Physics Institute, University of Zürich (Switzerland), February 22, 2001.

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A. de Visser, P. Estrela, M. J. Graf, A. Amato and A. Schenck, Magnetic quantum critical point and superconductivity in U(Pt,Pd)z International Conference on Strongly Correlated Electron Systems (SCES2001), Ann Arbor, Michigan (USA), August 6-10,2001.

G. M. Kalvius, E. Schreier, A. Kratzer, D. R. Noakes, R. Wappling, J. I. Espeso, J. C Gomez Sal, A. Amato, Ch. Baines, ßSR magnetic studies of CeNi\-xCux

International Conference on Strongly Correlated Electron Systems (SCES2001), Ann Arbor, Michigan (USA), August 6-10,2001.

D. Herlach, T. Albrecht, C. Bhrer, D. M. Herlach, D. Platzek, J. Reske, K. Maier, ¡JLSR an Co-Pd Legierungen im flüssigen, unterkühlten und im festen Zustand Symposium unterkühlte Metallschmelzen, 65. Physikertagung d. Deutschen Physikalischen Gesellschaft DPG, Hamburg (Germany), March 26 - 30, 2001.

D. Herlach (poster), Less is MORE - Muons on Request at PSI

Workshop: "Magnetic Resonance of Defects in Materials", Institute of Physics, London (UK), April 6, 2001.

R. Khasanov, A. Shengelaya, K. Conder, E. Morenzoni, I.M. Savic and H. Keller, Oxygen-isotope effect on the in-plane penetration depth in underdoped Yi-xPrxBa2CusOr-s as revealed by muon-spin rotation Swiss Workshop on materials with Novel electronic properties 2001, Les-Diablerets (Switzerland), October 1-3,2001. E. Morenzoni, Muon spin rotation and relaxation experiments on thin films Winter School of PNPI, Repino (Russia), February 20-24,2001.

E. Morenzoni, Penetration ofkeV muons in thin metallic films 19th International Conference on Atomic Collisions in solids, Paris (France), July 29 - August 3, 2001.

E. Morenzoni (invited talk), Muon spin rotation and relaxation experiments Seminar, Leiden University, Leiden (The Netherlands) June 22, 2001.

E. Morenzoni, The use of polarized low energy muons for the study of magnetic fields on the scale of a few nm Swiss Workshop on Materials with Novel Electronic Properties 2001, Les Diablerets (Switzerland), October 1-3, 2001.

T. Prokscha et al., ßSR experiments with low energy muons at PSI: present and future 12th International Conference on Hyperfine Interacions, Park City (USA), August 12-17,2001.

G. Solt, VS. Egorov, C. Baines, D. Herlach, U. Zimmermann, Condon Domains: Collective Magnetic Response of Electrons on Landau Orbitals Meeting of the Swiss Physical Society SPG, Dübendorf (Switzerland), May 2-3,2001.

A. Suter (invited talk), The Magnetic Resonance Force Microscope - Recent Development

Colloquium, Service de Physique de l'Etat Condens, CEA/Saclay (France), February 6, 2001.

A. Suter (invited talk), The Magnetic Resonance Force Microscope — A New Approach to Microscopic Subsurface Imaging Seminar, Physik Institut der Univeristät Zürich (Switzerland), March 13, 2001. A. Suter (invited talk), Quantum Computer— Why - How - When Colloquium, Univeristät Zürich (Switzerland), April 19, 2001.

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LABORATORY FOR MICRO A N D NANO TECHNOLOGY

B. Baumeister, T.A. Jung, E. Meyer Atomic force microscope investigations on fracture and erosion of nanostructures STM 01, Vancouver (Canada), 2001.

B. Baumeister, T.A. Jung, E. Meyer Bruchmechanische Untersuchungen an Nano strukturen unter Verwendung des Rasterkraftmikroskops DPG Tagung, Hamburg (Germany), 2001.

B. Baumeister, T A . Jung, E. Meyer Scanning force microscopy studies on fracture mechanics and erosive wear at the nanometer scale MRS Spring Meeting, San Francsico (USA), April 16, 2001.

B. Baumeister, T.A. Jung, E. Meyer Fracture studies and controlled modification of nanotowers using the scanning force microscope APS March Meeting, Seattle (USA), March 12, 2001.

S. Berner, M. Brunner, L. Ramoino, H. Suzuki, H. Yanagi, D. Schlettwein, T.A. Jung, H.-J. Giintherodt Two dimensional molecular motion confined by decorated terrace edges: dynamic equilibrium in a 2 dimensional 'molecular corrall'or 'bottle' 17 t h SAOG Meeting, University of Fribourg (Switzerland), January 25, 2001.

S. Berner , H. Suzuki, C. Loppacher, T. Kamikado, TA. Jung, E. Meyer, R. Bennewitz, R. Schüttler, S. Mashiko, H.-J.Güntherodt Conformational flexure and switching of single porphyrin molecules Japan Swiss Workshop on Nanoscience, Pontresina (Switzerland), September 25, 2001.

S. Berner, M. Brunner, L. Ramoino, H. Suzuki, T.A. Jung, H.-J. Giintherodt Two dimensional molecular solid-gas equilibrium observed by scanning tunneling microscopy Annual Meet, of the Swiss Physical Society, EMPA Dübendorf (Switzerland), May 2, 2001.

S. Berner S., L. Ramoino, H. Suzuki, T.A. Jung, H.-J. Güntherodt Direct observation of a molecular 2D solid-gas equilibrium by STM STM 01, Vancouver (Canada), July 15, 2001.

S. Berner, M. Brunner, L. Ramoino, H. Suzuki, H.-J. Güntherodt, T. A. Jung Two dimensional molecular solid-gas equilibrium observed by Scanning Tunneling Microscopy 20 t h European Conference on Surface Science, ECOSS, Krakow (Poland), September 4 - 7 , 2001.

A. Beyer, D. Grützmacher, J. Gobrecht Electrically stimulated IR luminescence from Ge quantum dots International Semiconductor Conference CAS, Sinaia (Romania), October 9 - 13, 2001.

A. Beyer, S. Stutz, H. Sigg, M. Goryll, T. Stoica, L. Vescan, D. Grützmacher Electro- and photoluminescence of C-induced Ge quantum dots First International Workshop on NEW GROUP IV (Si-Ge-C) SEMICONDUCTORS, Sendai (Japan), January 21 - 23, 2001.

A. Beyer, E. Müller, H. Sigg, S. Stutz, K. Ensslin, D. Grützmacher Electroluminescence of carbon-induced germanium islands in silicon 11th European Workshop on Molecular Beam Epitaxy, Hinterzarten (Germany), February 4 - 7 , 2001.

A. Beyer, E. Müller, S. Stutz, B. Haas, H. Sigg, C. David, D. Grützmacher Optische Eigenschaften von Germanium Inseln Seminar, Universität Hamburg (Germany), May 11, 2001.

A. Beyer, E. Müller, S. Stutz, H. Sigg, C. David, D. Grützmacher Germanium islands embedded in strained silicon quantum wells grown on patterned substrates Fourth International workshop "modelling, growth, properties and devices of epitaxial semiconductors on Novel Index Surfaces", Aspet (France), September 16 - 20, 2001.

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B. Bitnar Thermophotovoltaik - kostengünstige Elektrizitätserzeugung mit Gasheizungen Universität Hamburg (Germany), May 11, 2001.

B. Bitnar, W. Durisch, G. Palfinger Thermophotovoltaics - Technology and Applications Zentrum für Sonnenenergie- und Wasserstoff-Forschung (ZSW), Stuttgart (Germany), December 20, 2001.

B. Bitnar, W. Durisch, D. Grützmacher, J.-C. Mayor, F. von Roth, J.A. Anna Selvan, H. Sigg, H. R. Tschudi, J. Gobrecht

A TPV system with silicon photocells and a selective emitter 28 t h IEEE Photovoltaic Spec. Conf., Anchorage (Alaska), September 15 - 22, 2000.

B. Bitnar, W. Durisch, J.-C. Mayor, H. Sigg, H. R. Tschudi, G. Palfinger, J. Gobrecht Development of a small TPV prototype system with an efficiency > 2% 17 t h European Photov. Solar Energy Conf. and Exh. Munich (Germany), October 22 - 26, 2001.

M. Brunner, S. Berner, H. Suzuki, C. Loppacher, T. Kamikado, T.A. Jung, E. Meyer, R. Bennewitz, H.-J. Güntherodt Conformational flexure and switching of a single porphyrin molecule STM 01, Vancouver (Canada), July 15, 2001.

B.P. Cahill, L.J. Heyderman, J. Gobrecht, A. Stemmer Transport of sub-micron latex spheres by traveling-wave dielectrophoresis Nanotech 2001, Montreux (Switzerland), November 27 - 29, 2001.

C. David, V. Schlott, A. Jaggi A zone plate based beam monitor for the Swiss Light Sourc 5th European Workshop on Diagnostics and Beam Instrumentation DIPAC 2001, Grenoble (France), May 1 3 - 15, 2001.

C. David, B. Nöhammer, E. Ziegler, O. Hignette Tunable diffractive optical elements for hard x-rays SPIE - The International Society for Optical Engineering, Annual Meeting, San Diego (USA), July 30 - August 3, 2001.

C. David, B. Nöhammer, H. Solak, B. Haas, F. Glaus, J. F. van der Veen, V. Schlott, J. Bongaerts, B. Kaulich, J. Susini Diffractive x-ray lenses for photon energies ranging from extreme ultraviolett to hard x-rays SPIE - The International Society for Optical Engineering, Annual Meeting, San Diego (USA), July 30 - August 3, 2001.

C. David, P. Häberling, M. Schnieper, J. Söchtig, C. Zschokke Nano-structured anti-reflective surfaces replicated by hot embossing Micro- and Nano-Engineering MNE 2001, Grenoble (France), September 16 - 19, 2001.

C. David, B. Nöhammer, E. Ziegler Wet etching of linear Fresnel zone plates for hard x-rays Micro- and Nano-Engineering MNE 2001, Grenoble (France), Septemberl6 - 19, 2001

G. Dehlinger, L. Diehl, U. Gennser, H. Sigg, J. Faist, K. Ensslin, D. Grützmachera E. Müller Intersubband-Electroluminescencefrom Si/SiGe Quantum Cascade Structures SPIE Conference Photonics West, San Jose CA (USA), January 22 - 26, 2001.

G. Dehlinger, L. Diehl, U. Gennser, H. Sigg, E. Müller, S. Stutz, J. Faist, K. Ensslin, T. Roch, G. Bauer, J. Stangl, D. Grützmacher Growth and Characterisation of Si/SiGe Quantum Cascade Structures Deposited by Molecular Beam Epitaxy First International Workshop on New Group IV (Si-Ge-C) Semiconductors Control of Properties and Applications to Ultrahigh Speed and Opto-Electronic Devices, Sendai (Japan), January 21 - 23, 2001.

L. Diehl, G.Dehlinger, H. Sigg, U. Gennser, D. Grützmacher, E. Müller, J. Faist, K. Ennslin Application of the quantum cascade laser principle to the Si/SiGe material system CLEO, Conference on Lasers & Electro Optics, Baltimore, MD (USA), May 6 - 10, 2001.

L. Diehl, G.Dehlinger, H. Sigg, U. Gennser, D. Grützmacher, E. Müller, J. Faist Progress towards the realization of a Si/SiGe Quantum Cascade Laser ITQW 01, Intersubband Transitions in Qunatum Wells, Asilomar, Cal. (USA), September 10 - 14, 2001.

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W. Durisch, B. Bitnar, J.-C. Mayor, F. von Roth, H. Sigg, H. R. Tschudi, G. Palfinger Progress in the development of a small thermophotovoltaic prototype system 17 t h European Photov. Solar Energy Conf. and Exh. Munich (Germany), October 22 - 26, 2001.

U. Gennser, L. Diehl, G. Dehlinger, H. Sigg, D. Grützmacher^ E. Müller, J. Faist, K. Ensslin, I. Sagnes, D. Bensahel Intersubband quantum cascade in the Si/SiGe material system

10th International Conference on Modulated Semiconductor Structures, Linz (Austria), July 23 - 27, 2001.

J. Gobrecht Licht aus Silizium: Traum oder reale Chance?

Physik-Kolloquium, Friedrich Alexander Universität, Erlangen (Germany), January 29, 2001.

J. Gobrecht Einführung in die Nanowelt und deren physikalische Besonderheiten

Seminar on „Kunststoffe in der Nanotechnologie" at KATZ Aarau (Switzerland), March 1, 2001 and November 15, 2001.

J. Gobrecht, L. Tiefenauer Nanos trukturie rte Oberflächen für die Bioanalytik

3. Internationales WGP Symposium, Neue Technologien in der Medizin, Aachen (Germany), May 1 1 - 1 2 , 2001.

J. Gobrecht Self-Assembly in Multilayer Systems TOP NAN021 Seminar "Effiziente Herstellung dünner Schichten aus flüssigen NanomateriaUen", Fribourg (Switzerland), July 2, 2001. J. Gobrecht, D. Grützmacher, A. Beyer Near IR electroluminescence from Ge quantum dots formed by self-organisation "Japanese-Swiss Seminar on Nanoscience II", Pontresina (Switzerland), September 25 - 27, 2001. J. Gobrecht Nano science and technology: national programs and centers in Switzerland Europen co-operation in micro- and nanotechnologies, Sinaia (Romania), October 12, 2001. J. Gobrecht Mikro und Nano für die Biomedizinische Technik

Jahrestagung der Schweizerischen Ges. für biomedizinische Technik, Villigen (Switzerland), November 9, 2001.

J. Gobrecht Nanotechnologie: Grundlagen und ausgewählte Beispiele Hochrhein-Seminar für Mathematik und Naturwissenschaften, VilUgen (Switzerland), 29, 2001. D. Grützmacher, G. Dehlinger, L. Diehl, U. Gennser, H. Sigg, E. Müller, S. Stutz, J. Faist, K. Ensslin Si/SiGe Quantum Cascade Structures Emitting in the 10 jum range Seminar at RIKEN, Tokyo (Japan), January 25, 2001

D. Grützmacher, G. Dehlinger, A. Beyer, L. Diehl, U. Gennser, H. Sigg, E. Müller, S. Stutz, J. Faist, K. Ensslin Electroluminescence ofMBE Grown Si/SiGe(C) Nanostructures: Quantum Dots and Cascade Structures 1 I t h EURO-MBE Workshop in Hinterzarten (Germany), February 4 - 7 , 2201.

D. Grützmacher Sonnen-Neutrinos

Habilitationsvorlesung, Universität Konstanz (Germany), May 2, 2001.

D. Grützmacher Epitaxie von Si-Ge-C Nanostrukturen für Anwendungen in der Opto-Elektronik Max-Planck-Institut für Festkörperforschung, Stuttgart ( Germany), May 22, 2001. D. Grützmacher Si technology off the beaten path: Si-Ge-C Nanostructures for opto-electronic applications Seminar at Russian Academy of Science (Sibirian branch), Institute for Semiconductor Physics, Novosibirsk (Russia), June 2, 2001.

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D. Grützmacher Si/SiGe nanostructures: New paths for opto-electronics on Si Frontier Science Research Conference: Science and technology of Silicon Materials, La Jolla, California (USA), August 13 - 15, 2001.

D. Grützmacher Si - Ge - C Nanostructures: progress towards new device concepts Seminar at Motorola Research Center, Phoenix, Arizona (USA), August 16, 2001.

D. Grützmacher Si based opto-electronics: Potential ofSi-Ge-C Nanostructures

Seminar at IBM T.J. Watson Research Center, Yorktown Heights, New York (USA), August 17, 2001.

D. Grützmacher Fortschritte auf dem Wege zu SiGe basierter Opto-Elektronik MBE-Workshop Berlin 2001 (Germany), September 17 - 18, 2001. D. Grützmacher Epitaxie von Halbleiter-Nanostrukturen im Materialsystem Si-Ge-C Seminar at University of Erlangen, Lehrstuhl für Angewandte Physik / ZAE Bayern( Germany), November 12, 2001.

D. Grützmacher Epitaxie von Halbleite r-Nanostrukturen

Antrittsvorlesung, Universität Konstanz (Germany), October 13, 2001.

L.J. Heyderman, H. Schift Replication of micro- und nanostructures using molding techniques Seminar at University of Wuppertal, Institute for Microstructure Engineering Wuppertal (Germany), May 11, 2001.

L. Heyderman, B. Haas, B. Ketterer, L.Tiefenauer, R. Michel, A. Gössel, M. Textor Production of Nano-patterned materials for cell adhesion studies TOP Nano 21 meeting, Bern (Switzerland), October 16, 2001.

T. A. Jung The International Physicists Tournament: An alternative way of physics competition for high school physics teaching Physiktag für Lehrbeauftrage an Mittelschulen, Bundesamt für Messwesen, Wabern (Switzerland), September 18, 2001.

T. A. Jung Physik als Einstieg für viele Berufe: Die Rolle der Physik in Technologie und Gesellschaft Vortrag vor den Schwz. Teilnehmern der Internationalen Physikolympiade, Neue Kantonsschule Aarau (Switzerland), March 31, 2001.

B. Ketterer, L. Heyderman, B. Haas, L.Tiefenauer, O. Dubochet, P. Surbled, T. Hessler Nanostructured chips for the analysis of individual membrane proteins TOP Nano 21 meeting, Bern (Switzerland), October 16, 2001.

B. Ketterer, J. Gobrecht, R. Strümpler, J.-H. Fabian Feasibility of electromechnaical nano-switches NAREL TOP Nano 21 meeting, Bern (Switzerland), October 16, 2001.

E. Müller, O. Kirfel, A. Rastelli, H. von Känel, D. Grützmacher Investigation of the early stages of Si-overgrowth of Ge-dots on Si (001) Microscopy of Semiconducting Materials XII, Oxford (UK), March 25 - 29, 2001.

E. Müller Transmission Electron Microscopy of SiGe and Ge structures on Si Seminar at the Applied Physics Laboratory, ETH Zürich (Switzerland), May 22, 2001.

E. Müller, O. Kirfel, D. Grützmacher, A. Rastelli, H. von Känel Ge-Inseln auf Si (001) überwachen mit Si Einweihungsfeier zum neuen Mikroskop, Festkörper- und Angewandte Physik, ETH Zürich (Switzerland), October 11, 2001.

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E. Müller, O. Kirfel, A. Rastelli, H. von Känel, D. Grützmacher TEM study of the shape changes occuring during Si-overgrowth of Ge islands on Si (001 ) at growth temperatures up to 650 °C

Dreiländertagung für Elektronenmikroskopie, Innsbruck (Austria), September 9 - 14, 2001.

C. Padeste, B. Steiger, L. Tiefenauer Avidin-biotin based molecular architectures for electrochemical biosensors

Schweiz. Arbeitsgemeinschaft Oberflächen und Grenzflächen, 17 t h Meeting, Freiburg (Switzerland), January 25, 2001.

C. Padeste, B. Steiger, L. Tiefenauer Avidin-biotin based molecular architectures for electrochemical biosensors

6 t h Meeting on "Electrode reaction mechanisms and interfacial structure" Bad Kosen (Germany), April 5, 2001.

C. Padeste Microstructuring, nanotechnology and molecular architecture for biosensors and related applications. Seminar, Univ. Bochum Juni 7 & Univ. Bielefeld (Germany), Juni 8, 2001. G. Palfinger, B. Bitnar, W. Durisch, J.-C. Mayor, D. Grützmacher, J. Gobrecht Cost estimates of electricity from a TPV residential heating system 17 t h European Photov. Solar Energy Conf. and Exh. Munich (Germany), October 22 - 26, 2001. V. Ya. Prinz, D. Grützmacher, A. Beyer, C. David, B. Ketterer, E. Deckardt A new technique for fabricating 3-dimensional micro- and nano structure s of various shapes 9 t h international symposium on Nanostructures: Physics and technology, St. Petersburg (Russia), June 18 - 22, 2001

L. Ramoino, S. Berner, M. Brunner, L. Gade, L. Galea, T.A. Jung, H.-J. Güntherodt Deposition system for single molecule experiments for Scanning Tunneling Microscope Single Molecule Physics and Chemistry Workshop, Andermatt (Switzerland) 2001.

L. Ramoino, S. Berner, M. Brunner, H. Suzuki, H. Yanagi, D. Schlettwein, H.-J. Güntherodt, T. A. Jung Molecular adsorption and motion in a 2D gas-solid equilibrium. Gordon Research Conference on Thin Film and Crystal Growth Mechanisms Wilhams College, Williamstown, Massachusetts (USA), July 1 - 6 , 2001.

H. Schift Herstellung von Nano strukturen mittels Replikation: Verfahren und Anwendungen Seminars on „Kunststoffe in der Nanotechnologie" at KATZ Aarau (Switzerland), March 1, 2001 and November 15, 2001.

H. Schift, L.J. Heyderman, C. Padeste, J. Gobrecht Chemical nano-patterning using hot embossing lithography MNE 2001, Grenoble (France), September 17 - 19, 2001.

H. Schift, L.J. Heyderman, J. Gobrecht, M. Gale, J. Söchtig, W. Raupach, D. Simoneta Nanoreplication: NanoRep TOP Nano 21 meeting, Bern (Switzerland) October 16, 2001.

H. Sigg, G. Dehlinger, L. Diehl, U. Gennser, S. Stutz, J. Faist, D. Grützmacher, K. Ensslin, E. Müller Valenceband intersubband electroluminescence from Si/SiGe quantum cascade structures Advanced Research Workshop on Semiconductor Nanostructures, Queenstown (New Zealand), February 5 - 10, 2001.

H. Sigg, G. Dehlinger, L. Diehl, U. Gennser, S. Stutz, J. Faist, D. Grützmacher, E. Müller Si/SiGe quantum cascade intersubband emission

Conference on Middel Infrared Coherent Sources, MICS'2001, St. Petersburg (Russia), June 25 - 29, 2001.

H. Sigg Electroluminescence in Si/SiGe Quantum Cascade Structures Graduiertenkollegs 384 (Nanoelektronik, Mikromechanik und Mikrooptik) Lehrstuhl für Angewandte Festkoerperphysik Ruhr-Universitaet Bochum (Germany), June 7, 2000.

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H. Sigg Electroluminescence in Si/SiGe Quantum Cascade Structures Seminar at Paul Drude Institute, Berlin (Germany), June 11, 2000.

H. H. Solak X-ray Interferometric Lithography

Swiss Light Source Seminar, PSI VilUgen (Switzerland), March 2, 2001.

H. H. Solak, Y. Yang, F. Cerrina Observation of speckle patterns in extreme ultraviolet imaging

45* International EIPBN 29Conference, Washington DC (USA), May 29 - June 1, 2001.

H. H. Solak X-ray Interferometric Lithography SPS Annual Meeting, Dübendorf (Switzerland), May 2 - 3, 2001. H. H. Solak, C. David, J. Gobrecht, L. Wang, F. Cerrina Four-wave EUV interference lithography

Micro- and Nano-Engineering MNE 2001, Grenoble (France), September 16 - 19, 2001.

H. H. Solak X-ray Interference Lithography

European Synchrotron Radiation Facility Seminar, Grenoble (France), November 19, 2001.

H. Sorribas, L. Tiefenauer, J. Gobrecht System for extracellular recording of electrical signal from in-vitro cultivated neurons 35. Jahrestag. Deutschen Gesell, für Biomedizinische Technik Bochum (Germany), September 19, 2001. H. Sorribas, C. Padeste, P. Sonderegger, C. Stricker, L. Tiefenauer Neurochips functionalised with cell adhesion proteins Biosurf IV, Lausanne (Switzerland), September 20, 2001.

H. Suzuki, S. Berner, M. Brunner, H. Yanagi, D. Schlettwein, T. A. Jung, H.-J. Güntherodt Characterization of molecular overlayers on metal surfaces in dynamic equilibrium by Scanning Tunneling Microscope First International Conference on Molecular Electronics and Bioelectronics (M&BE1), Awaji Yumebutai International Conference Center, Kobe Bai, (Japan), March 5 -7, 2001.

H. Suzuki, S. Berner, M. Brunner, T.A. Jung, H. Yanagi, H.-J. Güntherodt Structure of subphthalocyanine overlayers on Ag surface and their dynamics 48* Spring meeting of Japanese Soc. of Applied Physics, Meiji University (Japan) March 28, 2001.

H. Suzuki, S. Berner, M. Brunner, T.A. Jung, H. Yanagi, D. Schlettwein, H.-J. Güntherodt Coordinated rotational flipping of subphthalocyanine molecules in extended 2D islands STM 01, Vancouver (Canada), July 15, 2001.

L. Tiefenauer Mikro- und Nanotechnologie für die Biowissenschaften Seminar EMPA St. Gallen (Switzerland), April 19, 2001.

L. Tiefenauer Micro- and nanotechnology for life sciences Seminar Univ. Neuchâtel (Switzerland), May 3, 2001.

L. Tiefenauer, H. Sorribas, C. Padeste Micropatterns of functional proteins for cell cultures

7* General meeting of the Swiss Society for Biomaterials, Waldenburg (Switzerland), May 16, 2001.

L. Tiefenauer Micro- and nano structuring for life sciences British-Swiss technology update and partnering days "Micro- and nanotechnologies in the Ufe sciences", Zürich (Switzerland), February 7, 2001.

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L. Tiefenauer Benefits from force measurements of individual ligand-receptor complexes 9 t h Swiss workshop of methodology in receptor research, ETH Zürich (Switzerland), September 23, 2001.

L. Tiefenauer, H. Sorribas, C. Strieker, C. Padeste Bio-functionalized neurochips 2 3 n d IEEE Conf. IEEE Engin. Med. & Biol. Soc., Istanbul (Turkey), October 25, 2001.

M. de Wild., S. Berner, H. Suzuki, C. Loppacher., T. Kamikado., T. A. Jung, E. Meyer, R. Bennewitz, H.-J.Güntherodt Conformational Flexure and Switching of a Single Porphyrin Workshop on Nanoscience, Twannberg (Switzerland), October 16 - 19, 2001.

LABORATORY FOR RADIO- AND ENVIRONMENTAL CHEMISTRY

H E A V Y E L E M E N T S

R. Dressier Nuclear structure near Z=108 and N=162

5 t h Workshop on the Chemistry of the Heaviest Elements, Hasliberg (Switzerland), August 26-29, 2001.

Ch.E. Düllmann Gaschemische Untersuchungen von Elementen der Gruppe 8 in Oxidsystem Seminar des Labors für Radio- und Umweltchemie, Universität Bern (Switzerland), June 15, 2001. Ch.E. Düllmann Gaschemical investigation of Hassium

5* Workshop on the Chemistry of the Heaviest Elements, Hasliberg (Switzerland), August 26-29, 2001.

Ch.E. Düllmann Gaschemische Untersuchung von Osmium und Hassium im Oxidsystem mit IVO und COLD

Poster contritubion Jahrestagung der GDCh-Fachgruppe Radiochemie, Würzburg (Germany), September 23-29, 2001.

Ch.E. Düllmann Gaschemical Investigation of Hassium (Hs, Z=108).

Meeting der ISOLDE-Gruppe CERN, Genf (Switzerland), December 12, 2001.

B. Eichler Adsorptionseigenschaften des Elements 112

Seminar des Labors für Radio- und Umweltchemie, Universität Bern (Switzerland), June 15, 2001.

B. Eichler Metallchemie der Transaktinoide

Jahrestagung der GDCh-Fachgruppe Radiochemie, Würzburg (Germany), September 23-29, 2001.

B. Eichler Adsorption der Transaktinoide auf Metalloberflächen

Seminar des Flerov Instituts für Kernreaktionen, Dubna (Russia), November 28, 2001

H.W. Gäggeler First chemical study ofbohrium with the OLGA technique and prospects for future studies of hassium and element 112

Dept. of Chemistry, University of Oslo (Norway), January 23, 2001.

H.W. Gäggeler Decay properties of some transactinide nuclides studied with the OLGA technique ISOL 01, Oak Ridge TN (USA), March 11-14, 2001.

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H.W. Gäggeler On-line gas chemistry as a tool to study nuclear decay properties and the chemical behaviour of heaviest elements European East-West Coordination Meeting on Nuclear Science, Sandanski Bulgaria, May 5-9, 2001.

H.W. Gäggeler Gas phase chemical studies of transactinides, Workshop on Very Heavy Nuclear Systems European Center for Theoretical Nuclear Physics, ECT, Trente (Italy), July 9-14, 2001.

H.W. Gäggeler Gas chemical studies of transactinides

Institute of Modern Physics, Lanzhou (China), August 9, 2001.

H.W. Gäggeler Chemische Untersuchungen mit einzelnen Atomen schwerster Elemente

Jahrestagung der GDCh-Fachgruppe Radiochemie, Würzburg (Germany), September 23-29, 2001.

H.W. Gäggeler, B. Eichler Semi-empirical calculations and gas chromato graphical determination of adsorption enthalpies of metals, oxides and chlorides

EURISOL/TARGISOL Meeting, CERN/ISOLDE (Switzerland), October 29-30, 2001.

H.W. Gäggeler Gas phase chemical studies of transactinides ACTINIDES 2001, Hayama (Japan), November 4-9, 2001. S. Soverna Miss Piggy als Quelle kurzlebiger Radioisotope

Seminar Radio- und Umweltchemie, Universität Bern (Switzerland), February 9, 2001.

S. Soverna Model studies of mercury for a future 112 experiment 5 t h Workshop on the Chemistry of the Heaviest Elements, Hasliberg (Switzerland), August 26-29, 2001. S. Soverna, H.U. Aebersold, Ch.E. Düllmann, B. Eichler, H.W. Gäggeler, L. Tobler, A. Türler, Q. Zhi Modellstudien an Quecksilber für ein künftiges 112-Experiment

Jahrestagung der GDCh-Fachgruppe Radiochemie, Würzburg (Germany), September 23-29, 2001.

S. Soverna, B. Eichler Model studies of mercury for a future 112 experiment

Seminar of the Flerov Laboratory of Nuclear Reactions, Dubna (Russia), November 28, 2001.

A.Türler Heavy Element Chemistry - Status and Perspectives (invited) 3 rd International Conference on Exotic Nuclei and Atomic Masses (ENAM 2001), Hämeenlinna (Finland), July 2-7, 2001. A. Türler Experimente zur chemischen Charakterisierung von Hassium (Hs, Z=108)

Jahrestagung der Fachgruppe Nuklearchemie der GDCh, Würzburg, Germany, 23-29 September, 2001.

A. Türler Gas Phase Chemistry Experiments with Transactinide Elements Sg (Z=106), Bh (Z=107), andHs (Z=108) (invited) 2 n d International Symposium on Advanced Science Research, ASR2001, Advances in Heavy Element Research, Tokai (Japan), November 13-15, 2001. S U R F A C E C H E M I S T R Y

M. Ammann, F. Arens, L. Gutzwiller, H.W. Gäggeler The reaction of HNO3 with sea-salt aerosol Poster contribution to the session OA21: Tropospheric aerosols: formation and heterogeneous chemistry, European Geophysical Society General Assembly EGS2000, Nice (France), March 25-28, 2001.

225

F. Arens Reaktion von N02 mit Anthrarobin

Seminar Labor für Radio- und Umweltchemie, Paul Scherrer Institute (Switzerland), May 11, 2001.

T. Bartels, M. Ammann, H.W. Gäggeler The Adsorption of Peroxyacetly Nitrate on Crystalline Ice - A Thermo-Cromatography Study Using 13N. Poster and short presentation at ERCA (European Research Course on the Atmospheres), Grenoble (France), January 8 - February 10, 2001. T. Bartels, M. Ammann, H.W. Gäggeler The Adsorption of PAN on ice Oral contribution to the s e s s ion OA23: Photochemistry of the tropical troposphere, European Geophysical Society General Assembly EGS2000, Nice (France), March 25-28, 2001.

T. Bartels, H.W. Gäggeler, M. Ammann The Adsorption of PAN on ice - Results and Method

Contribution to the CUT-ICE EU Project Annual Meeting, York (United Kingdom), May 21-22, 2001.

T. Bartels, H.W. Gäggeler, M. Ammann The Adsorption of Peroxyacetly Nitrate on Crystalline Ice - A Thermo-Cromatography Study Using BN oral contribution to session 7.3: Atmospheric Chemistry at the Air-Ice Interface, IAMAS International Association of Meteorology and Atmospheric Science Annual Meeting, Innsbruck (Austria), July 10-18, 2001. T. Bartels Adsorption of nitrogen oxides on ice: final results, mechanistical considerations and atmospheric relevance Seminar Labor für Radio- und Umweltchemie, Universität Bern (Switzerland), December 7, 2001.

C. Guimbaud Importance ofsnowpack in processing atmospheric acetaldehyde in the arctic boundary layer Seminar Labor für Radio- und Umweltchemie, Paul Scherrer Institute (Switzerland), May 11, 2001.

C. Guimbaud, M. Ammann, F. Arens, L. Gutzwiller, M. Wachsmuth, H.W. Gäggeler Kinetic study of the HN03 sea salt reaction in an aerosol flow reactor Poster, European Aerosol Conference, Leipzig (Germany), September 3-7, 2001.

L. Gutzwiller, M. Ammann Reactions ofN02 with semi-volatile organicsfrom diesel exhaust and VOC photooxidation Contribution to the NITROCAT EU Project Annual Meeting, Orléans (France), April 2-3, 2001.

L. Gutzwiller HONO Bildungskapazität von Dieselabgas

Seminar Labor für Radio- und Umweltchemie, Universität Bern (Switzerland), April 6, 2001.

L. Gutzwiller, F. Arens, M. Ammann New HONO Source involving Semi-Volatile Exhaust Organics Fate and Impact of Anthropogenic Emissions, 8thEuropean Symposium on the Physico-Chemical Behaviour of AtmosphericPollutants, Torino (Italy), September 17-20, 2001. A. Vlassenko Measurement of ammonium sulfate concentration in atmospheric aerosol in Siberian region Seminar Labor für Radio- und Umweltchemie, Universität Bern (Switzerland), December 7, 2001.

M. Wachsmuth, H.W. Gäggeler, M. Ammann A new approach to study HOBr - aerosol interactions Oral contribution to the session ST9: New chemistry in the atmosphere,

European Geophysical Society General Assembly EGS2000, Nice (France), March 25-28, 2001.

M. Wachsmuth Interaktion von markierten Bromverbindungen mit atmosphärenrelevanten Oberflächen Seminar Labor für Radio- und Umweltchemie, Universität Bern (Switzerland), February 9, 2001.

226

A N A L Y T I C A L C H E M I S T R Y H.W. Gäggeler Glaciers from the Alps as Archive of the European Atmosphere Workshop on Climate Change at High Elevation Sites: Emerging Impacts (HIGHEST II), Davos (Switzerland), June 25-28, 2001

H.W. Gäggeler Glaciochemical studies on Belukha (Altai) ARGUS 2001, Baikalsk (Russia), July 30 - August 5, 2001.

P. Ginot, M. Schwikowski. U. Schotterer, W. Stichler, H.W. Gäggeler, B. Francou, R. Gallaire, B. Pouyaud Climate variability reconstruction from Andean glaciochemical records Int. Symposium on Ice Cores and Climate, Kangerlussuaq (Greenland), Augustl9-23 , 2001.

P. Ginot Comparison ofglacio-chemical records from Chimborazo 1999 and 2000 cores Workshop on Andean ice cores, Grenoble (France), March 6, 2001.

T. Huber Kontinuierliches Schmelzen und ionenchromatographische Analyse von Eisbohrkernen Seminar Labor für Radio- und Umweltchemie, Paul Scherrer Institute (Switzerland), January 12, 2001.

Th. Jenk, M. Schwikowski, H.W. Gäggeler Search of a suitable ice archive in the Bernina area

1st Workshop in the VITA-project of the NCCR-Climate, University of Bern (Switzerland), October 25, 2001.

St. Knüsel Dating of the Illimani ice core

Workshop on Andean ice cores, Grenoble (France), March 6, 2001.

N.L. Misra Some studies on the applicability ofTXRFfor trace element analysis in ice samples Seminar Labor für Radio- und Umweltchemie, Universität Bern (Switzerland), February 9, 2001. S. Olivier Nachweis und Analyse von Staubhorizonten im Eis vom Cerro Tapado

Seminar Labor für Radio- und Umweltchemie, Universität Bern (Switzerland), February 9, 2001.

C. Schnabel 10Be und 10Be/7Be Verhältnisse zum Studium des Stratosphären-Troposphärenaustausches Seminar Labor für Radio- und Umweltchemie, Paul Scherrer Institute (Switzerland), May 11, 2001. U. Schotterer, H.U. Bürki, W. Stichler, W. Graf, L. Gourcy, T. Huber, P. Ginot Stable Isotopes in alpine ice cores: do they record climate variability? Conf. on the Study of Environmental Change Using Isotope Techniques, IAEA, Vienna (Austria), April 23 - 27,2001.

U. Schotterer, M. Grosjean, Chr. Kuli, P. Ginot, W. Stichler, H. W. Gäggeler, M. Schwikowski, B. Francou, R.Gallaire Climate Variability and Environmental Changes as Recorded in Glaciers from the Central Andes Workshop on Climate Change at High Elevation Sites: Emerging Impacts (HIGHEST II), Davos (Switzerland), June 25-28,2001.

M. Schwikowski Hochalpine Gletscher als Archive der Luftverschmutzung Fachtagung Gletscher als Umwelt- und Klimaarchiv, Jahresversammlung der Glaziologischen Kommission des S ANW, Universität Bern (Switzerland), January 25, 2001.

M. Schwikowski Potential for climate variability reconstruction from South American glaciochemical records Ice Fields Meeting, Centro de Estudios Científicos, Valdivia (Chile), September 20-21, 2001.

227

S. Szidat, H.W. Gäggeler, H.-A. Synal, I. Hajdas, G. Bonani, U. Baltensperger Radiocarbon (MC) Measurements on Particulate Organic Carbon in the Lower Troposphere EUROTRAC-AEROSOL-Workshop, Cologne (Germany), March 21-22, 2001.

S. Szidat Analyse von 129I in Umweltmaterialien Seminar Labor für Radio- und Umweltchemie, Paul Scherrer Institute (Switzerland), May 11, 2001.

S. Szidat, H.W. Gäggeler, H.-A. Synal, I. Hajdas, G. Bonani Bestimmung von ,4C in aerosolgebundenem Kohlenstoff

Jahrestagung der GDCh-Fachgruppe Radiochemie, Würzburg (Germany), September 23-29, 2001.

S. Szidat Iod-129: Probenvorbereitung, Qualitätssicherung und Analyse von Umweltmaterialien Jahrestagung der GDCh-Fachgruppe Radiochemie, Würzburg (Germany), September 23-29, 2001. S. Szidat, H.W. Gäggeler, H.-A. Synal, I. Hajdas, G. Bonani Bestimmung von I4C in aero sol gebundenem Kohlenstoff mit Beschleunigermassenspektrometrie (AMS) 18. Seminar Aktivierungsanalyse, Berlin, 25-26 October, 2001.

S. Szidat Radioecological Investigations of Iodine-129

Seminar für Kern- und Radiochemie, Universität Mainz (Germany), Novembe 21, 2001.

L. Tobler Bestimmung von Spurenelementen in alpinem Eis mit hochauflösender ICP-MS Seminar Labor für Radio- und Umweltchemie, Universität Bern (Switzerland), April 6, 2001.

L. Tobler Measurement of7Be and210Pb activity concentrations at the Jungfraujoch for the time period March 2000 - March 2001 Workshop EU STACCATO Project, Zurich (Switzerland), May 7-8, 2001

P R O J E C T R A D W A S T E J.P.M. Beijers, J. Benlliure, O. Bersillon, J. Blomgren, J. Cugnon, P. Eudes, D. Filges, A. Koning, J.-F. Lecolley, S. Leray, J.-P. Meulders, R. Michel, N. Olsson, K.-H- Schmidt, H. Schuhmacher, I. Slypen, H.-A. Synal, R. Weinreich HIND AS — A European project on High- and Intermediate-energy Nuclear Data for Accelerator-driven Systems International Conference "Nuclear Applications in the New Millenium", Reno (USA), November 12-16, 2001.

A. Koning, H. Beijers, J. Benlliure, O. Bersillon, J. Cugnon, M. Duijvestijn, P. Eudes, D. Filges, F. Haddad, S. Hilaire, C. Lebrun, F.-R. Lecolley, S. Leray, J.-P. Meulders, R. Michel, R. Neef, R. Nolte, N. Olsson, R. Ostendorf, E. Ramström, K.-H. Schmidt, H. Schuhmacher, I. Slypen, H.-A. Synal, R. Weinreich HIND AS - A European Nuclear Data Program for Accelerator-Driven Systems International Conference on Nuclear Data for Science and Technology (Japan), October 7-12, 2001.

R. Weinreich Separation schemes for radiochemical analysis of irradiated iron, lead, bismuth and uranium targets HINDAS Progress Meeting, Santiago de Compostela (Spain), March 16-17, 2001.

R. Weinreich (invited paper) Radioanalytical Chemistry in the determination of radionuclide inventory of accelerator waste 9th International Conference "Separation of Ionic Solutes", Bratislava, Modra-Harmónia (Slovakia), June 5-10, 2001.

R. Weinreich, M. Argentini Radiochemische Analyse von Beschleunigerabfällen. 2. Workshop "Radiochemische Analytik bei Betrieb und Rückbau kern technischer Anlagen, der Deklaration von Abfällen und im Strahlenschutz", Dresden (Germany), November 5-6, 2001.

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LABORATORY FOR ION BEAM PHYSICS

G. Bonani Radiokarbondatierung von Milligrammproben mit der Beschleunigermassenspektrometrie-Methode (AMS) Archäologisches Institut, Universität Zürich (Switzerland), May 7, 2001.

M. Christi, C. Strobl, P. W. Kubik, A. Mangini Beryllium in Deep sea Sediments: Reconstructing the Intensity of the Earth's Magnetic Field and Boundary Scavenging American Geophysical Union 2001 Fall Meeting, San Francisco (USA), December 10-14, 2001.

M. Christi, C. Strobl, S. Siegle, P. W. Kubik, A. Mangini Transport- und Sedimentationsprozesse von 10Be im Südatlantik

Ocean Drilling Program (ODP) colloquium, University of Karlsruhe (TH) (Germany), Febuary 28 - March 2, 2001.

M. Döbeli Exposure age dating by fluorine diffusion 7th European Conference on the Application of Accelerators in Research and Technology, Guildford (England), August, 21 2001. M. Döbeli Beschleunigung von Molekülen - Not und Tugend Physikalische Gesellschaft Zürich (Switzerland), December 6, 2001.

C J. Fogwill, P. W. Kubik In Patagonia: the dynamics of Late Glacial climatic change

Quaternary Research Association Postgraduate Symposium, Univ. of St Andrews (UK), September 10-12, 2001.

C J. Fogwill, P. W. Kubik, D. Sugden, W. M. Phillips The application of in situ cosmogenic exposure dating (10Be), to glacial deposits of the Last Déglaciation in the southern Andes of Chile. Earth System Processes Conference, London (UK), June 24-28, 2001. C.J. Fogwill, P.W. Kubik, W.M. Phillips The application of cosmogenic exposure dating to glacial deposits of the Last Déglaciation in the southern Andes of Chile European Union of Geosciences Conference, Strasbourg (France), August 8-12, 2001.

M. Frank, A.N. Halliday, N. Whiteley, R.K. O'Nions, P.W. Kubik, J.R. Hein Nd and Pb isotope evolution of Atlantic deep-water masses: Evidence for variations in water mass exchange and weathering inputs over the past 20 Myr

American Geophysical Union 2001 Fall Meeting, San Francisco (USA), December 10-14, 2001.

I. Hajdas, G. Bonani, J. McManus, M. Mendelson, S. Hemming Variations in atmospheric 14C content 40,000 years ago and the radiocarbon age of Heinrich Event 4 EuroConference on Achieving Climate Predictability Using Paleoclimate Data, Castelveccio Pascoli (Italy), November 10-15, 2001. T. Hewawasam, F. von Blanckenburg, M. Schaller, P. Kubik The effects of deforestation on soil erosion in tropical highlands (Sri Lanka) as quantified by cosmogenic nuclides Bi-annual meeting of the European Union of Geosciences, Strasbourg (France), April 2001

T. Hewawasam, F. von Blanckenburg, M. Schaller, P. W. Kubik Cosmogenic nuclide quantification of extremely low natural erosion and dramatic increases in soil loss by deforestation in tropical highlands (Sri Lanka) American Geophysical Union 2001 Fall Meeting, San Francisco (USA), December 10-14, 2001.

R. Hetzel, S. Niedermann, S. Ivy-Ochs, P.W. Kubik, M. Tao 21Ne versus 10Be surface exposure ages of quartzite: A comparison Jahrestagung Deutsche Mineralogische Gesellschaft, Potsdam (Germany), September 14-19, 2001.

229

R. Hetzel, S. Niedermann, M. Tao, S. Stokes, P. W. Kubik, S. Ivy-Ochs Slip rates of active thrusts in the Qilian Shan (China) based on 21Ne and 10Be exposure ages of Late Pleistocene alluvial fans and luminescence dating of Holocene loess deposits 16 t h Himalaya-Karakoram-Tibet-Workshop, Graz (Austria), April 3-5, 2001.

S. Ivy-Ochs, H. Kerschner, P. W. Kubik, C. Schliichter Chronology of Last Glacial Maximum to Holocene glacier advances in the European Alps based on surface exposure dating PAGES International Conference, Aix-en-Provence (France), August 2 7 - 3 1 , 2001.

J. Karthu, S. Tschudi, S. L. Vartanyan, P. W. Kubik, M. Saarnisto Implications of rock surface exposure ages for the latest glacial advance on Wrangel Island in the Beringian region, Russia

European Union of Geosciences Conference, Strasbourg (France), August 8-12, 2001

M.A. Kelly, C. Schliichter, P. W. Kubik Reconstruction and surface exposure-age dating of the last ice cap in the western Alps American Geophysical Union 2001 Fall Meeting, San Francisco (USA), December 10-14, 2001. M. A. Kelly, C. Schliichter, P. W. Kubik Reconstruction and surface exposure-age dating of the last ice sheet in the western Alps ESF-EURESCO Conference, II Ciocco (Italy), November 10-15, 2001.

P. W. Kubik Langlebige kosmogene Nuklide an der Erdoberfläche: Werkzeuge zur Charakterisierung von Landschaftsentwicklungen Seminar, Universität Hannover (Germany), April 19, 2001.

I. Leya, R. Wieler, G. F. Herzog, C. Schnabel, P. Ma Helium, Neon, and Argon in Canyon Diablo Spheroids 32 n d Lunar and Planet. Sei. Conf., Houston (USA), March 12-16, 2001.

C. Maden Application of gas ionisation detectors in accelerator mass spectrometry Doktorandenseminar, ETH Zürich, October 11, 2001.

R. Michel, Th. Ernst, S. Szidat, Ch. Schnabel, H.-A. Synal Langfristige Entwicklung von Iod-129 in der Umwelt Klausurtagung des Radioökologieausschusses der SSK, Klais (Germany), July 25-26, 2001.

R. Michel, Th. Ernst, S. Szidat, Ch. Schnabel, H.-A. Synal Iodine-129 as a long-lived tracer in the environment Int. Conf. on the Study of Environmental Change using Isotope Techniques", IAEA, Vienna (Austria), April 23-27, 2001.

R. Muscheler, J. Beer, G. Wagner, P. W. Kubik, H.-A. Synal Changes in past solar activity derived from cosmogenic radionulide records - is there a connection to climate proxy records? 6th ELDP Workshop, Potsdam (Germany), May 12, 2001

R. Muscheler, J. Beer, G. Wagner, C. Laj, A. Mazaud, C. Kissel, P. W. Kubik Past canges in the carbon cycle inferred from a comparison of14C and 10Be records American Geophysical Union 2001 Fall Meeting, San Francisco (USA), December 10-14, 2001.

M. M. Rutgers van der Loeff, M. Frank, P. W. Kubik, A. Mangini Conservative behaviour of10Be in the water column of the Weddell Sea and the Atlantic sector of the Antarctic Circumpolar Current? American Geophysical Union 2001 Fall Meeting, San Francisco (USA), December 10-14, 2001.

J. M. Schäfer, S. Ivy-Ochs, U. Ninnemann, G.H. Denton, C. Schlüchter, R. Wieler, P. W. Kubik, B. G. Andersen, P. Schlosser Rise and fall of the Last Glacial Maximum in New Zealand - Terrestrial and marine evidence from Southern mid latitudes NOAA CORC ARCHES Annual Conference, Lamont-Doherty Earth Observatory, November 28, 2001.

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J. M. Schäfer, S. Ivy-Ochs, U. Ninnemann, G.H. Denton, C. Schlüchter, R. Wieler, P. W. Kubik, B. G. Andersen, P. Schlosser Structure of the Last Glacial Maximum in New Zealand - Terrestrial and marine evidence from Southern mid latitudes American Geophysical Union 2001 Fall Meeting, San Francisco (USA), December 10-14, 2001.

M. Schaller, F. von Blanckenburg, N. Hovius, P. W. Kubik Paleo-erosion rates from in situ 10Be in Middle European river terrace sediments American Geophysical Union 2001 Fall Meeting, San Francisco (USA), December 10-14, 2001.

C. Schnabel, L. Tobler, P. W. Kubik, M. Schwikowski, H. W. Gäggeler Be-7, Pb-210, Be-10, and Be-10/Be-7 at Jungfraujoch Workshop of the STACCATO project of the European Union, Zürich (Switzerland), May 8-9, 2001.

C. Schnabel, L. Tobler, P. W. Kubik, M. Schwikowski, H. W. Gäggeler Be-7, Pb-210, Be-10, and Be-10/Be-7 at Jungfraujoch Workshop of the STACCATO project of the European Union, Freising (Germany), October 29-30, 2001.

C. Schnabel, P. Ma, G. F. Herzog, T. Faestermann, K. Knie, G. Korschinek 10Be, 26Al, and 53Mn in martian meteorites 3 2 n d Lunar and Planet. Sei. Conf., Houston (USA), March 12-16, 2001.

C. Schnabel, P. Ma, G. F. Herzog, M. L. di Tada, P. A. Hausladen, L. K. Fifield Terrestrial Ages of Canyon Diablo Meteorites 64* Annual Meeting Meteoritical Soc , Vatican City (Vatican), September 10-14, 2001.

C. Schnabel, I. Leya, R. Wieler, R. K. Herd, H.-A. Synal, U. Krähenbühl, G. F. Herzog 129I in Knyahinya and Abee and a first estimate ofGCR constancy over 20 Myr 64* Annual Meeting Meteoritical Soc , Vatican City (Vatican), September 10-14, 2001.

M. Suter Advances in accelerator mass spectrometry at sub-MeV energies

Frühjahrstagung der Deutschen Physikalischen Gesellschaft, Berlin (Germany), April 1 - 6 , 2001.

M. Suter Accelerator masssSpectrometry at sub-MeV-energies - new results and prospects 15* International Conference on Ion Beam Analysis, Cairns (Australia), July 1 5 - 2 0 , 2001.

M. Suter Accelerator masssSpectrometry at sub-MeV-energies - new results and prospects 222 n d ACS National Meeting, Chicago (USA), August 26 - 30, 2001.

M. Suter Accelerator mass spectrometry atsSub-MeV-energies - new results and prospects

Seminar, Lamont-Doherty Earth Observatory of Columbia University, Palisades, N.Y. (USA), August 28, 2001.

M. Suter Accelerator mass spectrometry — instrumental developments and applications Seminar, Lecce Tandetron Laboratory, Brindisi (Italy), September 7, 2001. M. Suter Accelerator mass spectrometry — instrumental developments and applications

The XIX Autumn School on "New Perspectives with Nuclear Radioactivity", Lisbon (Portugal), October 8 - 13, 2001.

M. Suter Accelerator mass spectrometry — instrumental developments and applications

General FANTOM Study Week on Applications of Accelerators, Gent (Belgium), November 12 - 16, 2001.

H.-A. Synal The Zürich AMS facility European Community Project Meeting HINDAS, Santiago de Compostela (Spain), March 16, 2001.

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H.-A. Synal Radionuclide record in Mid-Latitude glacier ice from the Tien Shan mountains (Kyrghyzstan) Frühjahrstagung der Deutschen Physikalischen Gesellschaft, Berlin (Germany), April 2, 2001.

H.-A. Synal Alpine Gletscher als Klimaarchive: Expeditionsbericht über eine Eisbohrung im Tien Shan Gebirge (Kyrghyzstan) Seminar Universität Wien, Vienna (Austria), May 2, 2001.

H.-A. Synal Status of AMS: 41 Ca measurements

European Community Project Meeting OSTEODIET, Interlaken (Switzerland), May 29, 2001.

H.-A. Synal Long-lived radionuclides in ice Core records:What can we learn ? Int. Conf. on Ice Cores and Climate, Kangerlusuaq (Greenland), August 21, 2001.

H.-A. Synal AMS measurements of long-lived radionuclides European Community Project Meeting HINDAS; Zurich (Switzerland), September 29, 2001.

S. Tschudi, S. Ivy-Ochs, C. Schlüchter, P. W. Kubik, H. Rainio New 26AI dates for the Younger Dryas Salpausslekä I formation in Finland European Union of Geosciences Conference, Strasbourg (France), August 8-12. 2001

T. Van de Flierdt, M. Frank, A. N. Halliday, B. Hattendorf, D. Günther, P. W. Kubik, J. R. Hein Local and regional inputs of lead in Pacific deep water over the past 20 Myr American Geophysical Union 2001 Fall Meeting, San Francisco (USA), December 10-14, 2001.

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PUBLICATIONS AND LECTURES FOR GENERAL PUBLIC

M. Audard L'Astronomie X au 3ème Millénaire Kiwanis-Club Lausanne, Lausanne, January 22, 2001

R. Eichler Physik Begreifen Volkshochschule Zurzach, PSI-Forum Villigen, January 17, 2001.

R. Eichler Let's Bez Bezirksschule Leuggern, Leuggern, January 20, 2001

R. Eichler Physik Begreifen Ärzte von Baden, PSI-Forum, Villigen, August 8, 2002

R. Eichler Forschung am PSI

Schülertage am PSI, Villigen, October 26, 2001 and November 22, 2001

R. Eichler Experimentelle Methoden der Teilchenphysik Vortrag, Mittelschule Wohlen, September 2001. M. Fivian Solar Coronal Physics and HESSI Urania-Sternwarte Zürich, May 5, 2001

J. Gobrecht Forschungsgebiet Nanotechnologie: Zwischen science fiction und realer Anwedung Schweizerischer Technischer Verband STV, PSI-Forum, Villigen, September 12, 2001.

M. Suter Neue Methoden für Datierungen in der Klima- und Erdgeschichte Volkshochschule Friedrichshafen, March 13, 2001.

M. Suter Radioaktivität als Werkzeug zur Altersbestimmung Festival des Wissens, ETH Zürich, Zürich, May 9, 2001.

A. Zehnder X-ray Astronomie Schweizerische Raumfahrt - Vereinigung, April 2001.

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LECTORES AND COURSES

Prof. Dr. R. Eichler ETH Zürich, SSOl: • Physik II für Mathematiker und Physiker • Physikpraktikum für Vorgerückte • Particle Physics Seminar (with others) • Physikalisches Kolloquium (with others) • Teilchenphysikpraktium am PSI ETH Zürich, WS01/02: • Physik I für Mathematiker und Physiker • Particle Physics Seminar (with others) • Physikalisches Kolloquium (with others)

L A B O R A T O R Y FOR ASTROPHYSICS

Dr. M. Güdel ETH Zürich und Universität Zürich, SSOl: • Physik der Stern- und Planetenentstehung ETH Zürich und Universität Zürich, WS00/01: • Hochenergie-Astrophysik (with Prof. A. Benz)

L A B O R A T O R Y FOR MICRO A N D N A N O T E C H N O L O G Y

Dr. J. Gobrecht ETH Zürich, WS01/02: • Vorlesung und Übungen „Grundlagen der Mikro- und Nanotechnik"

Dr. J. Gobrecht und Dr. H. Schift Fachhochschule Aargau, SSOl • Vorlesung „Nanotechnik für Ingenieure"

Dr. T.A. Jung Universität Basel, WS01/02:

• Vorlesung "Einführung in die Nanowissenschaften" (with others)

Dr. H. Sigg Universität Zürich, WSOl/02: • "VP Halbleiterpraktikum" (together with Prof. B. Patterson)

L A B O R A T O R Y FOR RADIO A N D ENVIRONMENTAL CHEMISTRY

Prof. Dr. H. W. Gäggeler Universität Bern, SSOl: • Physikalische Chemie IV: Radio- und Elektrochemie • Praktikum Physikalische Chemie II • Instrumentalanalytik II • Seminar in anorganischer Chemie (with others) • Kolloquium Radio- und Umweltchemie in collaboration with Paul Scherrer Institut (organized

by Dr. M. Ammann) Universität Bern, WSOl/02: • Anwendung von Radioisotopen • Blockpraktikum Umwelt- und Radiochemie • Physikalisch-chemisches Wahlpraktikum • Seminar in anorganischer Chemie (with others) • Kolloquium Radio- und Umweltchemie in collaboration with Paul Scherrer Institut (organized

by Dr. M. Ammann)

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• Methoden der Biochemie I • Methoden der Biochemie I. Übungen

Dr. M. Schwikowski Universität Bern, SSOO: • Instrumentalanalytik II (with Prof. H.W. Gäggeler)

L A B O R A T O R Y FOR ION B E A M PHYSICS

Dr. M. Döbeli ETH Zürich, SS01: • Kernphysik CERN Accelerator School, Pruhonice, Czeque Republic, May 2001 • Material Analysis

Prof. Dr. M. Suter ETH Zürich, SS01: • Seminar "Kern- und Teilchenphysik mit Anwendungen" (with others) • Vorlesung und Übungen "Physik III" (für Umweltnaturwissenschafter) (with others) • Kernphysikpraktikum für Vorgerückte • Doktorierendenseminar über Kern- und Teilchenphysik (with others) ETH Zürich, WS01/02: • Seminar "Kern- und Teilchenphysik mit Anwendungen" (with others) • Physikpraktikum für Vorgerückte (with others) • Kernphysik II, Wahlfachvorlesung • Kernphysikpraktikum für Vorgerückte

Dr. H.-A. Synal ETH Zürich, September 12-13 • Vakuumkurs der Schweizerischen Vakuumgesellschaft (SVG)

L A B O R A T O R Y FOR PARTICLE PHYSICS

THEORY G R O U P

PD Dr. A. Denner ETH Zürich, WS01/02: • Das Standardmodell der elektroschwachen Wechselwirkung und dessen Erweiterungen PSI Villigen, SS01 and WS01/02: • Seminar über Physik der Elementarteilchen

PD Dr. K. Junker Technische Universität Wien, SS01: • Einführung in die theoretische Mittelenergiephysik

PD Dr. R. Rosenfelder ETH Zürich, WS01/02: • Pfadintegrale in der Quantenphysik

PD Dr. M. Spira ETH Zürich, WS01/02: • Physik jenseits des Standardmodells (with F. Pauss)

L A B O R A T O R Y FOR M U O N SPIN SPECTROSCOPY

PD Dr. E. Morezoni ETH Zürich, WS01/02: • Physik mit Myonen: Von der Atomphysik bis zur Festkörperphysik

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AWARDS

Titels:

B. Bitnar, H. Sigg G. Palfînger (with others from ENE) Award for best poster

Progress in the Development of a small Thermophotovoltaic Prototype System 17 t h European Photovoltaic Solar Energy Conference and Exhibition, Munich (Germany), October 22 - 26, 2001

L. Diehl, G. Dehlinger Award: SPS (Swiss Physical Society) Price (donated by IBM) In apprecation of the first observation of electroluminescence in p-type Si/SiGe Quantum Cascade Heterostructure Dübendorf, May 2, 2001

E. Morenzoni Member of Isis Selection Panel Muons 2001-2003

S. Tschudi A.F. Schläfli Award of the Swiss Acadamy of Natural Sciences Oberflächenaltersdatierung von Glazialereignissen der Nordhalbkugel

Habilitation:

D. Puy: Title of thesis: L'âge sombre ou la première lumière Université de Savoie-Chambery

D. Grützmacher Title of thesis: A Material Science Endeavour of Low Dimensional Si-Ge-C Structures: Technology, Physics and Devices Universität Konstanz

Doctoral Thesis:

B. Baumeister: Title of thesis: Elementare Prozesse der Nanotribologie in Rasterkraftmikroskopie-Experimenten PSI

Thesis advisors: Prof. E. Meyer, (Universität Basel) Dr. T. Jung (PSI)

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G. Dehlinger: Title of thesis: Vertical Transport and Intersubband Emission in SiGe PSI

Thesis advisors: Prof. K. Ensslin (ETH Zürich) Dr. U. Ennser (PSI)

U. D ö t s c h : Title of thesis: Präparation und Untersuchungen von Einzel-Loch-Transistoren in p-dotierten Silizium - Ge rmanium -Hete ro strukturen PSI

Thesis advisors: Prof. K. Ensslin (ETH Zürich) Dr. C. David and Dr. U. Gennser (PSI)

J.-H. Fabian: Title of thesis: Mikromechanische Oszillatoren für die thermisch-gravimetrische Analyse PSI

Thesis advisors: Prof. E. Meyer, (Universität Basel) Dr. J. Gobrecht and Ph. Lerch (PSI)

M. Gärtner: Title of thesis: On-Line Gaschromatographie von Polonium und Elementen der Gruppe 6 des Periodensystems PSI / Universität Bern

Thesis advisors: Prof. Dr. H.W. Gäggeler (Universität Bern & PSI) Prof. Dr. B. Eichler (PSI)

P. Ginot: Title of thesis: Glaciochemical study of ice cores from Andean glaciers PSI / Universität Bern

Thesis advisors: Prof. Dr. H.W. Gäggeler (Universität Bern & PSI) Dr. M. Schwikowski (PSI)

Ch. Hilbes : Title of thesis: Towards an Experimental Test of Time Reversal Invariance Violation in the Decay of Polarized Free Neutrons PSI / ETH Zürich

Thesis advisors: Prof. Dr. J. Lang (ETH Zürich) Prof. Dr. K. Bodek (JU Cracow) Prof. Dr. W. Fetscher (ETH Zürich) PD Dr. J. Sromicki (ETH Zürich) Dr. A. Kozela (PSI / IFJ Cracow)

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T. Huber: Title of thesis: Bestimmung historischer Spurenstoffverläufe in alpinem Firn mittels kontinuierlicher ionenchromatographischer Analyse PSI / Universität Bern

Thesis advisors: Prof. Dr. H.W. Gäggeler (Universität Bern & PSI) Dr. M. Schwikowski (PSI)

S. Jacob: Title of thesis: Beschleunigermassenspektrometrie (AMS) von 14C bei tiefen Energien ETH Zürich

Thesis advisors: Prof. Dr. J.O. Lang (ETH Zürich) Prof. Dr. M. Suter (ETH Zürich) Prof. Dr. W. Kutschera (Universität Wien)

R. Kaufman: Title of thesis: Development of Hard Radiation Pixel Sensors for the CMS Experiment PSI / Universität Zürich

Thesis advisors: Prof. Dr. C. Amsler (Universität Zürich) Dr. R. Horisberger (PSI)

M. Pleines: Title of thesis: Untersuchung zur magnetischen Eindringtiefe in YBa2Cu307-Filmen mit niederenergetischen Myonen PSI / Universität Konstanz

Thesis advisors: PD E. Morenzoni (PSI) Prof. Dr. G. Schatz (Universität Konstanz) PD Dr. Ch. Niedermayer (Universität Konstanz)

R.Pohl: Title of thesis: Investigation of the long-lived metastable 2S state in muonic hydrogen PSI / ETH Zürich

Thesis advisors: Prof. Dr. H. Hofer (ETH Zürich) Prof. Dr. L. Schaller (Universität Fribourg) Dr. F. Kottmann (ETH Zürich)

S. Pozzorini: Title of thesis: Electroweak radiative corrections at high energies PSI / Universität Zürich

Thesis advisors: PD Dr. A. Denner (PSI / ETH Zürich) Prof. D. Wyler (Universität Zürich)

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F. Rosenbaum: Title of thesis: Suche nach der leptonflavorverletzenden Myon-Elektron-Konversion in Gold, ß'Au—>e'Au PSI / Universität Zürich

Thesis advisors: Prof. Dr. R. Engfer (Universität Zürich) Dr. W. Berti (PSI)

Ch. Salt: Title of thesis: DNA-seeking Gadolinium Complexes for Neutron Capture Therapy PSI / Universität Basel

Thesis advisors: Prof. Dr. T.A. Kaden (Universität Basel) Dr. R. Weinreich (PSI)

H. Sorribas: Title of thesis: Neurochips Functionalised with Cell Adhesion Proteins PSI

Thesis advisors: Prof. R. Douglas (Uni/ETH Zürich) Dr. L. Tiefenauer (PSI)

M. Wachsmuth: Title of thesis: Development of a short-lived bromine isotopes source for heterogeneous atmospheric chemistry experiments PSI / Universität Bern

Thesis advisors: Prof. Dr. H.W. Gäggeler (Universität Bern & PSI) Dr. M. Ammann (PSI)

D. Zürcher: Title of thesis: Studies of Resonant and Non — Resonant Weak Boson Pair Production at LHC PSI / ETH Zürich

Thesis advisors: Prof. Dr. F. Pauss (ETH Zürich) Dr. D. Renker (PSI)