High-Spin States In Ce-136 - Systematics Of Collective Oblate Rotation

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.