The level structure of the transitional even-even ${}_{}{}^{136}{}_{}{}^{}\mathrm{Ce}$ nucleus has been investigated using the ${}_{}{}^{122}{}_{}{}^{}\mathrm{Sn}$${(}^{18}$O, 4nγ) reaction. The prominent structure observed at high spin is a ΔI=1 rotational band, populated with ∼25% intensity of the $2^{+}$→$0^{+}$ transition, which has a low dynamic moment of inertia <20${\mathrm{ħ}}^2$ ${\mathrm{MeV}}^{\mathrm{-}1}$ for frequencies below ħω=0.45 MeV. This band is interpreted in terms of a two-quasiproton-two-quasineutron configuration with a shape close to the collectively rotating γ=-60° oblate shape, and is related to the oblate π${\mathit{h}}_{11/2}$⊗[ν${\mathit{h}}_{11/2}$${]}^2$ configuration seen in several nearby odd-Z nuclei. The systematics of such oblate rotational bands in this mass region are discussed. Other ΔI=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 ∼57${\mathrm{ħ}}^2$ ${\mathrm{MeV}}^{\mathrm{-}1}$, built on the highly deformed [ν${\mathit{i}}_{13/2}$${]}^2$ prolate configuration.

• Received 11 December 1989

DOI:https://doi.org/10.1103/PhysRevC.41.1576