High-spin states in 136Ce: Systematics of collective oblate rotation.

Abstract

The level structure of the transitional even-even $^{136}\mathrm{Ce}$ nucleus has been investigated using the $^{122}\mathrm{Sn}$${(}^{18}$O, 4n\ensuremath{\gamma}) reaction. The prominent structure observed at high spin is a \ensuremath{\Delta}I=1 rotational band, populated with \ensuremath{\sim}25% intensity of the ${2}^{+}$\ensuremath{\rightarrow}${0}^{+}$ transition, which has a low dynamic moment of inertia 20${\mathrm{\ensuremath{\Elzxh}}}^{2}$ ${\mathrm{MeV}}^{\mathrm{\ensuremath{-}}1}$ for frequencies below \ensuremath{\Elzxh}\ensuremath{\omega}=0.45 MeV. This band is interpreted in terms of a two-quasiproton-two-quasineutron configuration with a shape close to the collectively rotating \ensuremath{\gamma}=-60\ifmmode^\circ\else\textdegree\fi{} oblate shape, and is related to the oblate \ensuremath{\pi}${\mathit{h}}_{11/2}$\ensuremath{\bigotimes}[\ensuremath{\nu}${\mathit{h}}_{11/2}$${]}^{2}$ configuration seen in several nearby odd-Z nuclei. The systematics of such oblate rotational bands in this mass region are discussed. Other \ensuremath{\Delta}I=2 bands, built on states including ${\mathit{h}}_{11/2}$ quasineutron orbitals, are also associated with collective oblate rotation. In addition, tentative evidence is presented for a weak band (2% intensity), showing an enhanced dynamic moment of inertia \ensuremath{\sim}57${\mathrm{\ensuremath{\Elzxh}}}^{2}$ ${\mathrm{MeV}}^{\mathrm{\ensuremath{-}}1}$, built on the highly deformed [\ensuremath{\nu}${\mathit{i}}_{13/2}$${]}^{2}$ prolate configuration.