Spectroscopy of Se-76: Prolate-to-oblate shape transition

The spectroscopy of $^{76}\mathrm{Se}$ has been studied using the $^{70}\mathrm{Zn}(^{12}\mathrm{C}, \ensuremath{\alpha}2{\mathrm{n})}^{76}\mathrm{Se}$ fusion evaporation reaction. The yrast band of $^{76}\mathrm{Se}$ has been extended to substantially higher spin, allowing observation of the second band crossing. The much-delayed ${g}_{9/2}$ proton-pair alignment is discussed in terms of the cranked shell model and most likely is caused by a shape transition from prolate to oblate along the yrast line occurring in $^{76}\mathrm{Se}$. Based on the systematic investigation of the band crossings associated with the ${g}_{9/2}$ quasiparticle alignments and their relationships with the shape evolutions in the even-$A$ Se and Kr isotopes, a comprehensive picture of shape evolution along with spin and isospin in these nuclei is obtained.