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Title: Enhanced γ -Ray Emission from Neutron Unbound States Populated in β Decay

Total absorption spectroscopy was used to investigate the β -decay intensity to states above the neutron separation energy followed by γ -ray emission in 87,88Br and 94Rb. Accurate results were obtained thanks to the careful control of systematic errors. An unexpectedly large γ intensity was observed in all three cases extending well beyond the excitation energy region where neutron penetration is hindered by low neutron energy. The γ branching as a function of excitation energy was compared to Hauser-Feshbach model calculations. For 87Br and 88Br the branching reaches 57% and 20% respectively, and could be explained as a nuclear structure effect. Some of the states populated in the daughter can only decay through the emission of a large orbital angular momentum neutron with a strongly reduced barrier penetrability. In the case of neutron-rich 94Rb the observed 4.5% branching is much larger than the calculations performed with standard nuclear statistical model parameters, even after proper correction for fluctuation effects on individual transition widths. The difference can be reconciled introducing an enhancement of one order-of-magnitude in the photon strength to neutron strength ratio. An increase in the photon strength function of such magnitude for very neutron-rich nuclei, if it proved to bemore » correct, leads to a similar increase in the (n, γ) cross section that would have an impact on r process abundance calculations.« less
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  1. Univ. of Valencia (Spain). Institute of Corpuscular Physics
  2. Univ. of Surrey, Guildford (United Kingdom). Dept. of Physics
  3. Univ. de Nantes, Nantes (France)
  4. Univ. of Jyvaskyla (Finland). Dept. of Physics
  5. Univ. of Helsinki (Finland). Helsinki Institute of Physics
  6. Petersburg Nuclear Physics Institute, Gatchina (Russia)
  7. Universitat Politecnica de Catalunya, Barcelona (Spain)
  8. Centre for Energy, Environment and Technology (CIEMAT), Madrid (Spain)
  9. Argonne National Lab. (ANL), Argonne, IL (United States). Nuclear Engineering Division
  10. Brookhaven National Lab. (BNL), Upton, NY (United States)
Publication Date:
Report Number(s):
Journal ID: ISSN 0031-9007; PRLTAO; R&D Project: EST-003-NEFA; KB0301041
Grant/Contract Number:
SC00112704; AC02-06CH11357; FPA2008-06419; FPA2010-17142; FPA2011-24553
Accepted Manuscript
Journal Name:
Physical Review Letters
Additional Journal Information:
Journal Volume: 115; Journal Issue: 6; Journal ID: ISSN 0031-9007
American Physical Society (APS)
Research Org:
Brookhaven National Laboratory (BNL), Upton, NY (United States)
Sponsoring Org:
USDOE Office of Science (SC)
Country of Publication:
United States
OSTI Identifier:
Alternate Identifier(s):
OSTI ID: 1209177