Physics Seminar

Enhanced Octu-pole Collectivity in N > 50 Sr Nuclei
by Dr. Elena Stefanova, Texas Southern University
2008-04-23, 10:00 AM in NSB 148

Abstract

High-spin states of the nuclei 89,90Sr were studied via the reaction 82Se(11B,p2n) at abeam energy of 37 MeV with the GASP spectrometer at Legnaro, Italy. The nucleus 91,92Sr was produced at high spins as fission fragments following the fusion reaction 36S +159Tb at 165 MeV. Gamma rays were detected with the GAMMASPHERE array. The level schemes were considerably extended. Different than the neighboring nuclei, a change of the parity in the main sequences of both nuclei is suggested. Level structures were interpreted in terms of the spherical shell model. The calculations give a good overall description of the observed states. The high-spin levels of 91Sr and 92Sr were observed for the first time and the high-spin structure of 90,91,92Sr was investigated and interpreted for the first time. A persistent dramatically enhanced vibrational octu-pole collectivity in the main yrast sequences of all these nuclei was found. That is a feature quite different than the observed in the neighboring nuclei. Although, it was known that this is one of the regions of very law quadru-pole vibrational collectivity at low spin, we found that this very law quadru-pole collectivity persists at higher spins (at least up to 16+) as well. An experimental suggestion for the theoretically proposed before proton p3/2-p1/2 orbital quenching was observed as well.