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Radioactive beam spectroscopy of 212 Po and 213 At with the EXOGAM array

Nick Thompson University of Surrey. Radioactive beam spectroscopy of 212 Po and 213 At with the EXOGAM array. Aim. The production of high spin states in 212 Po and 213 At Analysis of resulting spectra to look for: New transitions population of spin states contamination.

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Radioactive beam spectroscopy of 212 Po and 213 At with the EXOGAM array

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  1. Nick Thompson University of Surrey Radioactive beam spectroscopy of 212Po and 213At with the EXOGAM array

  2. Aim The production of high spin states in 212Po and 213At Analysis of resulting spectra to look for: • New transitions • population of spin states • contamination

  3. 8He radioactive beam Produced by SPIRAL facility at GANIL through fragmentation 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 beamfor ~4.5 and 0.5 days respectively 209Bi (50 mg/cm2)for ~1 day

  4. Reactions 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-

  5. Detection 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 to singles Fig.2.1 Fig.3. Fig.4.1 Diagrams: http://www.ganil.fr/exogam/

  6. Analysis Main fusion-evaporation products are 212Po and 213At. 209Pb and 210Bi also created through single neutron pick-up between 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 and210Bi [R B Firestone et al.,Table of Isotopes, Eighth edition, Wiley, New York, 1996]

  7. Analysis 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 spectra from coincidence data 727 keV 2+→ 0+ gate

  8. Analysis Evidence 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-parity yrast 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] Gate on 868 Gate on 577 69

  9. Relative intensity comparison of our 8He beam work and 9Be induced reaction performed by A R Poletti et al.Nucl. Phys. A473, 595 (1987)

  10. Conclusions • 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+

  11. Many thanks to my collaborators 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 • 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, Denmark Also thanks to my sponsors BNFL

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