High spin states and a collective oblate band in137Ce

Abstract

High spin states in the $N=79$ ${}^{137}\mathrm{Ce}$ nucleus have been studied with the reaction ${}^{124}\mathrm{Sn}{(}^{18}\mathrm{O}{,5n)}^{137}\mathrm{Ce}$ at beam energy 78 MeV. The level scheme has been expanded with spin up to $\frac{43}{2}\ensuremath{\Elzxh}.$ At low spins, the yrast collective structure built on the $\ensuremath{\nu}{h}_{11/2}^{\ensuremath{-}1}\ifmmode\times\else\texttimes\fi{}{2}^{+}$ multiplet shows a transitional shape with $\ensuremath{\gamma}=30.8\ifmmode^\circ\else\textdegree\fi{}$ according to calculations of the triaxial rotor-plus-particle model. The configurations for several high spin states have been discussed from a systematical comparison with neighboring nuclei. A collective band built on $I=33/2$ level has been observed for the first time. This band has an oblate shape with $\ensuremath{\gamma}=\ensuremath{-}60\ifmmode^\circ\else\textdegree\fi{}$ and most probably originates from the five-quasiparticle $\ensuremath{\nu}{s}_{1/2}\ensuremath{\bigotimes}[\ensuremath{\nu}{h}_{11/2}{]}^{2}\ensuremath{\bigotimes}\ensuremath{\pi}{g}_{7/2}\ensuremath{\bigotimes}\ensuremath{\pi}{h}_{11/2}$ configuration.