Coriolis alignment and band crossing of the h9/2 proton band in 175,177,179,181Re

Preliminary data on a rotational band in ¹⁷⁵Re produced by the reaction ¹⁵⁹Tb(²⁰Ne,4n) at 102 MeV have been acquired. The yrast band built upon the 1/2^-[541] orbital was constructed from the experimental data as an extension of the systematics of the h_9/2 bands known in ^177,179,181Re. The level scheme of the h_9/2 proton band for this isotopic series was fitted by a Coriolis model. The calculations require an increasing energy separation between the 1/2^-[541] and 3/2^-[532] Nilsson orbitals for decreasing neutron number (N), which is in qualitative agreement with the trend expected for decreasing hexadecapole (ε₄) deformation.

A Cranked Shell Model (CSM) calculation was also performed to fit this h_9/2 band in this isotopic series. The calculation gives a fairly accurate fit of the level energies in the rotating frame to within ± 70 keV. Our analysis also indicates that the aligned angular momentum of this h_9/2 band is smoothly increasing from 2.9 ℏ for A = 175 to 3.6 ℏ for A = 181. This trend in alignments is nicely reproduced by the CSM calculations. The i_13/2 neutron crossing frequency, as indicated by the CSM calculation, is shifted upward as a result of larger deformation of the nucleus when excited into the h_9/2 proton state.