Post on 16-Jun-2019
Günter Weber EMMI Workshop, GSI, 7. 6. 2010
H. Bräuning1, S. Hess1,3, U. Spillmann1, A. Surzhykov2, S. Fritzsche1, R. Märtin1,2,S. Trotsenko1,4, D. Thorn5, D. Winters1 and Th. Stöhlker1,2,4
1 Gesellschaft für Schwerionenforschung, 64291 Darmstadt, Germany2 Universität Heidelberg, 69120 Heidelberg, Germany3 Universität Frankfurt, 60235 Frankfurt, Germany4 Helmholtz-Institut Jena, 07743 Jena, Germany5 Extreme Matter Institute, 64291 Darmstadt, Germany
Günter Weber1,2
Physikalisches Institut
Position sensitive x-ray detectors applied toCompton polarimetry of hard x-ray radiation
Günter Weber EMMI Workshop, GSI, 7. 6. 2010
Outline of the Talk
• Introduction to Compton Polarimetry
• Recent measurements at the ESR storage ring→ Radiative Electron Capture (REC)
→ Lyman-α1 radiation
→ Elektron-Nucleus Bremsstrahlung
• Bremsstrahlung measurements at thepolarized electron source SPIN at TU Darmstadt(very preliminary)
• Summary & Outlook
Günter Weber EMMI Workshop, GSI, 7. 6. 2010
Where do we find polarized x-rays?
AstronomySynchrotron radiation
ESRFCrabnebular
Aligned atomic systems
X-ray scattering(Compton, Rayleigh)RR/REC process Bremsstrahlung
EKIN
ωh
K
L
K-REC
∞
20 40 60 80 100102
103
104
105
photon energy [ keV ]
100 keV e- → Cabon
Günter Weber EMMI Workshop, GSI, 7. 6. 2010
Why should we care?
General interest
Revealing subtle details of atomic dynamics and structure(Lyman radiation in H-like systems)
Of special interest, if angular distribution is not accessible(EBIT, Astronomy)
Possible applications ?(Ion beam spin diagnosis, Imaging, Material science)
But: Precise polarimetry studies in the hard x-ray regime are quite challenging.
Günter Weber EMMI Workshop, GSI, 7. 6. 2010
10-1 100 101 102 103 104 105 106 107
Bragg Reflection
Photoionization
Thomson Scattering Pair Production
Compton Scattering
Crystal Optics
Liquid Crystals
photon energy [ keV ]
Polarimetry Techniques
MicropatternGas Counters
x-ray Optics
PrismLCD
Segmented SolidState Detectors
Günter Weber EMMI Workshop, GSI, 7. 6. 2010
0
30
60
90
120
150
180
210
240
270
300
330
ϕ
E
Polarization Measurement via Compton Scattering
Klein-Nishina Equation for Compton Scattering:
)cos θsin2'
'()'(21 2
c222
0 ϕωω
ωω
ωωσ
−+=Ω h
h
h
h
h
hrdd
Günter Weber EMMI Workshop, GSI, 7. 6. 2010
E
Standard Solid State Detectors
ScatteredPhotonDetector
Scatterer
0
30
60
90
120
150
180
210
240
270
300
330
E
Compton Polarimeter Setups
Günter Weber EMMI Workshop, GSI, 7. 6. 2010
Scatteringand Photon Detection
Segmented X-ray Detector
E
Compton Polarimeter Setups
Günter Weber EMMI Workshop, GSI, 7. 6. 2010
32x32 strips → 1024 pixels
64x64 mm → 4096 mm2 active area
Energy (2.5 keV FWHM) + Timing (100 ns) + 2D Position (2 mm) + Multihit Capability
Position sensitive Si(Li) detectoras a Compton Polarimeter
7 mm
64 mm
64 mm
B implantedp+ contact (32 strips)
Li driftedcontact (32 strips)
Dedicated for efficient and precise polarization studies from 70 keV to a few 100 keV
Günter Weber EMMI Workshop, GSI, 7. 6. 2010
Compton scattered photon distribution
0 30 60 90 120 150 180 210 240 270 300 330 3600
200
400
600
800
exp fit
Klein-Nishina formular
scattering angle ϕ
ϕ
E
From ϕ Distribution to Polarization
Projection on the ϕ angle
Online analysis already yields qualitative results!
K-REC Xe54+ → H2
S. Hess, Phd thesis (2010)
Günter Weber EMMI Workshop, GSI, 7. 6. 2010
SIS
ESR
11.4 MeV/uU73+
5 - 400 MeV/uU92+ up to
1000 MeV/u U92+
UNILAC
The GSI Accelerator Facility
Ions: H+ to U92+
Intensity: 108
Frequency: 106
Günter Weber EMMI Workshop, GSI, 7. 6. 2010
Ion Beam
Gas Target ( H2, N2, He, Ne, Ar, Xe )
The ESR internal gas target
Standard X-ray Detectors&
Novel Compton Polarimeters
Günter Weber EMMI Workshop, GSI, 7. 6. 2010
X-ray detector
Particle detector(MWPC)
Gastarget
Dipol magnet
Measurements at the ESR storage ring
25 50 75 100 125 150 1750
2000
4000
6000
8000
10000
K-RECU92+→ H
2 @ 96,6 MeV/u
∞-RECM-REC
Ly-α2
Cou
nts
Energy [ keV ]
coincient anti-coincident
L-REC Ly-α1
Bremsstrahlung
Typical HCI x-ray spectrum at the ESR
Inverse kinematics
→ Coincidence measurements between x-rays and ions!
Günter Weber EMMI Workshop, GSI, 7. 6. 2010
EKIN
ωhK
L
K-REC
∞
Radiative Recombination (RR)Radiative Electron Capture (REC)
In the non-relativistic approximation the REC radiation has dipole characteristics:
• sin2 θ angular distribution
• 100% linear polarization
E
B
e-
dipole
E
B
EB
e-
e-Time reversal process of photoionization
Günter Weber EMMI Workshop, GSI, 7. 6. 2010
ion beam
targ
etga
s
K-REC
hω
E
50 100 150 200 250 300 350 400 450 500 5500.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
degr
ee o
f the
line
ar p
olar
izat
ion
projectile energy (MeV/u)
Energy dependence
Observation angle θ=60°
First REC polarization measurements
U92+ → N2
S. Tashenov, Phd thesis (2005)
β = 0.4
β = 0.7
16 Pixel Ge(i) detector
Günter Weber EMMI Workshop, GSI, 7. 6. 2010
Line
ar P
olar
izat
ion
Observation angle ( deg )
preliminary
Xe54+ → H2 @ 150 MeV/u U92+ → N2, H2
100 MeV/u
400 MeV/u
800 MeV/u
Recent K-REC polarization measurements
Si(Li) Polarimeter S. Hess, Phd thesis (2010)
16 pixel detector S. Tashenov et al., PRL 97 (2006)
Photon emission angle ( deg )
mid-Z high-Z
preliminary
A gain by a factor 3 to 5 in precision!
Günter Weber EMMI Workshop, GSI, 7. 6. 2010
Study of Lyman-α1 polarization inH-like, high-Z systems
L-R
EC
1s1/2
2p3/2
Ly-α1
µ=+3/2µ=+1/2µ=-1/2µ=-3/2
99%M2 1% (in U91+)
Alignment of the excited 2p3/2 state:
Ly-α1 linear polarization:
Taking into account E1-M2-interference:E1
Revealing details of the population mechanism
Günter Weber EMMI Workshop, GSI, 7. 6. 2010
Lyman-α1 Polarization of U91+
Exakt relativistic calculations by A. Surzhykov:
E1-M2 interference in Ly-α1 leads to
Increased Anisotropy
Decreased Polarization
preliminary
U92+ → H2@ 96.6 MeV/u
Hyperf. Interact. 146-147 (2003)
G. Weber, unpublished
Günter Weber EMMI Workshop, GSI, 7. 6. 2010
EquationObservable Experiment Theoryonly E1 E1 + M2
Decoupling of the collision dynamics (alignment parameter A2) and the atomic structure (amplitude ratio α = M2/E1) leads to a model independent estimation of both values.
-> Precise estimation of the E1-M2 transition ratio!
A model independent estimationof the E1-M2 transition ratio
Amplitude ratioTheoryTheory
Günter Weber EMMI Workshop, GSI, 7. 6. 2010
REC/RR into Rydbergseries limit
Bremsstrahlunghigh energyend‐point
=
Xe54+ → H2 @ 150 MeV/u
G. Weber, unpublished
First Bremsstrahlung polarization study with inverse kinematics
preliminary
Next step:Bremsstrahlung polarimetry + electron spectroscopy -> correlation study
Günter Weber EMMI Workshop, GSI, 7. 6. 2010
• 100 keV electrons
• longitudinal or transversal electron polarization (about 80%)
• DC mode
C. Heßler, Conf. Proc. EPAC08 (2008)
Measurements at the polarized electron source SPIN at TU, Darmstadt
Experimental Set-up
Günter Weber EMMI Workshop, GSI, 7. 6. 2010
Linear Bremsstrahlung polarization measurements(unpolarized electrons)
preliminary
e-→ Au, 90µg/cm2 @ 130°
e-→ C, 210µg/cm2 @ 60°
KαKβ
ReconstructedCompton events for
98.5±3, 92.5±3, 86.5±3, 80.5±3,
74.5±3 keV
Bremsstrahlung
R. Märtin, unpublished
Linear Polarization
No corrections for systematic effects (electron scattering, polarimeter efficiency, etc.) done yet.
Günter Weber EMMI Workshop, GSI, 7. 6. 2010
100 keV electron beam
E
S
S. Tashenov, unpublished
Longitudinal pol. e-
1
22tan PP=χ
χ
P2 is proportionalto the degree ofspin polarization
The effect of spin polarized collision systems on Bremsstrahlung polarization
Au
Transversely pol. e-
Photon energy: 98.5±3 keVR. Märtin, unpublished
preliminaryχ = 9°
Günter Weber EMMI Workshop, GSI, 7. 6. 2010
Summary & Outlook
Effifcient and precise Compton polarimeters are available(only small systematic corrections needed)
Experiments have already revisited a variety of radiative processeswith respect to linear polarization (e.g. REC, Lyman, Bremsstrahlung)
Thank you for your attention!
Photon energies from about 70 keV to several 100 keV
Future plans:Studies of scattered x-rays at DESYPhoton-photon and photon-electron correlationsMeasurements at EBIS/T facilities