High spin states of ${}_{}{}^{65}{}_{}{}^{}\mathrm{Ge}$ have been investigated via the ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$${(}^{28}$Si,2pn${)}^{65}$Ge reaction at 93 MeV beam energy. A level scheme containing 36 new transitions and 20 new levels could be established on the basis of γγ and γγn coincidences, γ-angular distributions and γ-linear polarization measurements. The aim of the work was to study the softness with respect to octupole deformation as theoretically predicted for the lightest Ge and Se isotopes. We could definitely show that the excitation energy of the 15/$2^{\mathrm{-}}$ state (i.e., the coupling of the ${\mathit{g}}_{9/2}$ neutron to the $3^{\mathrm{-}}$ octupole state in ${}_{}{}^{64}{}_{}{}^{}\mathrm{Ge}$) is not strongly lowered in comparison to the neighboring Ge nuclei, but fits reasonably well into the trend of smoothly rising energy with decreasing neutron number. Consequently, it should be concluded that the lightest Ge isotopes do not display enhanced octupole correlations, at least in the energy range of ${\mathit{E}}_{\mathit{x}}$≤5 MeV.

• Received 3 May 1995

DOI:https://doi.org/10.1103/PhysRevC.52.1783