Physics Seminar

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.