Radioactive beam Radioactive beam spectroscopy of spectroscopy of 212212Po and Po and

213213At with the EXOGAM At with the EXOGAM arrayarray

Nick Thompson

University of Surrey

AimAim

The production of high spin states in 212Po and 213At

Analysis of resulting spectra to look for:

● New transitions● population of spin states● contamination

8He radioactive beam8He radioactive beamProduced by SPIRAL facility at GANIL throughfragmentation of 13C primary beam on thick carbon target.[M Lewitowicz, Nucl. Phys. a734, 645c (2004)]

8He particles (T1/2 = 119 ms) accelerated to 28 MeV

Av. intensity 2x105 ions/s ~2x that of previous experiment. [Zs Podolyak et al., Nucl. Inst. and Meth. in Phys. Res A511, 354 (2003)]

Targets: 208Pb (30 and 50 mg/cm2) in beam for ~4.5 and 0.5 days respectively

209Bi (50 mg/cm2) for ~1 day

ReactionsReactions

● Excited states of 212Po and 213At populated with (8He, 4n) reactions

● Both with cross section ~500mb

● 8He + 208Pb → 216Po* → 212Po* + 4n● 8He + 209Bi → 217At* → 213At* + 4n

also important from beam:● 8He → 8Li* + β-

Detection systemDetection system

Four EXOGAM Compton-suppressed clover detectors in the“gamma-cube configuration”

with the average distance from target to detector at 68mm the full-energy-peak efficiency at 662 keV was 13.5%

data acquisition master trigger set tosingles

Diagrams: http://www.ganil.fr/exogam/

AnalysisAnalysis

Main fusion-evaporation products are 212Po and 213At.

209Pb and 210Bi also created through single neutron pick-upbetween beam and target.

All these nuclei have been studied previously:

212Po [A R Poletti et al. Nucl. Phys. A473, 595 (1987)]213At [G J Lane et al.,AIP Conference Proceedings, 656, 386c (2003)]209Pb and 210Bi [R B Firestone et al.,Table of Isotopes, Eighth edition, Wiley, New York, 1996]

AnalysisAnalysis

spectra from coincidence data 727 keV 2+ → 0+ gate

212Po decay scheme based in work by A R Poletti et al. Nucl. Phys. A473, 595 (1987) and T R McGoram, M.Sc Thesis, University of Aukland, New Zealand (1997), and to be published

18+ state at 2921.0 keV α-decays to 208Pb ground state

AnalysisAnalysisEvidence is found for a previously unreported 69 keV transition(13-) → (12+) in gated γ-γspectra with conditions that at least two Clovers fire in the same event (within 2 μs)

182.8(4) keV (14+) →(12+) transition seen, completing even-parityyrast states to spin 14+ this has previously been observed in coincidence with α particles following the 9Be reaction [T R McGoram, M.Sc Thesis, University of Aukland, New Zealand (1997), and to be published]

69

Gate on 577

Gate on 868

Relative intensityRelative intensitycomparison of our 8He beam work and 9Be induced reactionperformed by A R Poletti et al. Nucl. Phys. A473, 595 (1987)

ConclusionsConclusions

Possible new transition identified at 69 keV Sighting of 182.8 keV transition (previously seen but not

available in general literature Apparent increase in population of higher spin states to 12+

213At preliminarily observed to spin (39/2-) - work in progress

Continuing search for peak in spectra which might be attributable to a state higher than 18+

A.B. Garnsworthy1, Zs. Podolyák1, P.M. Walker1, S.J. Williams1, G.D. Dracoulis2, G. de France4, G.J.Lane2, K. Andgren1,5, A.M. Bruce6, A.P. Byrne2,3, W.N. Catford1, B. Cederwall5, G.A. Jones1,

B. McGuirk7, S. Mandal8 E.S. Paul7, V. Pucknell9, N. Redon10, B. Rosse10, R.J. Senior2 and G. Sletten11

Many thanks to my Many thanks to my collaboratorscollaborators

– 1. Department of Physics, University of Surrey, Guildford GU2 7XH, UK

– 2. Dept. of Nuclear Physics, Australian National University, Canberra, Australia

– 3. Dept. of Nuclear Physics, The Faculties, Australian National University, Canberra, Australia

– 4. GANIL, BP 5027, Caen Cedex F-14021, France

– 5. Department of Physics, Royal Institute of Technology, S-106 91, Stockholm, Sweden

– 6. School of Engineering, University of Brighton, Brighton BN2 4GJ, UK

– 7. Department of Physics, University of Liverpool, Liverpool, L69 3BX, UK

– 8. GSI, Planckstrasse 1, Darmstadt D-64291, Germany

– 9. CLRC Daresbury Laboratory, Warrington, WA4 4AD, UK

– 10. Institut de Physique Nucleaire de Lyon, Lyon, France

– 11. Niels-Bohr-Institute, DK-2100 Copenhagen, DenmarkAlso thanks to my sponsors BNFL