The structure of the $N\approx Z$ nuclei ${}^{66}\mathrm{Ge}$ and ${}^{68}\mathrm{Ge}$ is studied by the shell model with an extended $P+\mathrm{QQ}$ Hamiltonian in the configuration space ($2p_{3/2},1f_{5/2},2p_{1/2},1g_{9/2}$). This framework can be shown to give a consistent and good description of energy levels, moments of inertia, and Q moments in Ge isotopes. We also investigate particle alignments and nuclear shapes in ${}^{66}\mathrm{Ge}$ and ${}^{68}\mathrm{Ge}$. It is shown that structural changes in the four sequences of the positive- and negative-parity yrast states with even J and odd J are caused by various types of particle alignments in the $g_{9/2}$ orbit. The nuclear shape is also investigated by calculating spectroscopic Q moments of the first and second $2^{+}$ states, and the triaxiality is examined by potential energy surface.

• Received 21 September 2004

DOI:https://doi.org/10.1103/PhysRevC.71.044301