1. Beta-decay of nuclei around Se-90. Search for signatures of a N=56 sub-shell closure relevant the r-process
- Author
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Quinn, M., Aprahamian, A., Pereira, J., Surman, R., Arndt, O., Baumann, T., Becerril, A., Elliot, T., Estrade, A., Galaviz, D., Ginter, T., Hausmann, M., Hennrich, S., Kessler, R., Kratz, K. -L., Lorusso, G., Mantica, P. F., Matos, M., Moller, P., Montes, F., Pfeiffer, B., Portillo, M., Schatz, H., Schertz, F., Schnorrenberger, L., Smith, E., Stolz, A., Walters, W. B., and Wohr, A.
- Subjects
Nuclear Experiment - Abstract
Nuclear structure plays a significant role on the rapid neutron capture process (r-process) since shapes evolve with the emergence of shells and sub-shells. There was some indication in neighboring nuclei that we might find examples of a new N=56 sub-shell, which may give rise to a doubly magic Se-90 nucleus. Beta-decay half lives of nuclei around Se-90 have been measured to determine if this nucleus has in fact a doubly-magic character. The fragmentation of Xe-136 beam at the National Superconducting Cyclotron Laboratory at Michigan State University was used to create a cocktail of nuclei in the A=90 region. We have measured the half lives of twenty-two nuclei near the r-process path in the A=90 region. The half lives of As-88 and Se-90 have been measured for the first time. The values were compared with theoretical predictions in the search for nuclear-deformation signatures of a N=56 sub-shell, and its possible role in the emergence of a potential doubly-magic Se-90. The impact of such hypothesis on the synthesis of heavy nuclei, particularly in the production of Sr, Y and Zr elements was investigated with a weak r-process network. The new half lives agree with results obtained from a standard global QRPA model used in r-process calculations, indicating that Se-90 has a quadrupole shape incompatible with a closed N=56 sub-shell in this region. The impact of the measured Se-90 half-life in comparison with a former theoretical predication associated with a spherical half-life on the weak-r-process is shown to be strong.
- Published
- 2011
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