Rotational band structure in 75Se.

Abstract

The high-spin states of $^{75}\mathrm{Se}$ have been investigated using the $^{59}\mathrm{Co}$ ${(}^{19}$F, 2pn) reaction at 55 MeV. The positive-parity band has been extended to ${\mathit{I}}^{\mathrm{\ensuremath{\pi}}}$=29/${2}^{+}$ and the unfavored signature has been identified. The negative-parity band has been extended to ${\mathit{I}}^{\mathrm{\ensuremath{\pi}}}$=19/${2}^{\mathrm{\ensuremath{-}}}$ and band crossings were observed for the first time in both bands. Eleven new lifetimes were measured using the Doppler-shift attenuation method which allowed for extraction of transition strengths and transition quadrupole moments. The B(M1) strengths exhibit a staggering dependent on the signature splitting. Calculations based on the Woods-Saxon-Bogolyubov cranking model explain the signature-dependent alignment process in the ${\mathit{g}}_{9/2}$ bands and predict signature inversion in all bands at high rotational frequencies. It is argued that the data are consistent with the transition from triaxial shapes with \ensuremath{\gamma}\ensuremath{\sim}-30\ifmmode^\circ\else\textdegree\fi{}, characteristic of one-quasiparticle configurations, to triaxial shapes with \ensuremath{\gamma}\ensuremath{\sim}30\ifmmode^\circ\else\textdegree\fi{}, characteristic of a three-quasiparticle configuration containing one aligned pair of ${\mathit{g}}_{9/2}$ protons.