The neutron-deficient nucleus ${}^{66}\mathrm{Ge}$ was populated at high spin in two experiments using the reaction ${}^{40}\mathrm{Ca}{(}^{32}\mathrm{S},\alpha 2p)$ at beam energies of 105 and 95 MeV. In the first experiment, a self-supporting ${}^{40}\mathrm{Ca}$ target was used, while a gold-backed target of similar thickness was used in the second experiment. $\gamma$ rays were detected with the EUROBALL array, combined with the charged-particle detector array EUCLIDES and the Neutron Wall. The level scheme of ${}^{66}\mathrm{Ge}$ was extended up to $E\approx 18\mathrm{MeV}$ and $I^{\pi }{=(23\mathrm{}}^{-}).\mathrm{}$ Above angular momentum ${10}^{+},$ we found two sequences, connected by energetically staggered $\Delta I=1\mathrm{}\hspace{0.5em}M1\mathrm{}$ transitions. The total Routhian surface calculations describe ${}^{66}\mathrm{Ge}$ at lower spins as a $\gamma$-soft nucleus having a moderate deformation of ${\beta }_2\approx 0.23,$ while a triaxial deformation is predicted for the band structures above $I^{\pi }{=10\mathrm{}}^{+}.$ To our knowledge, this is the first observation of staggered $M1\mathrm{}$ transitions in a deformed four-quasiparticle $\pi {(g}_{9/2}^2\left)\nu {(g}_{9/2}^2\right)$ structure.

• Received 16 January 2003

DOI:https://doi.org/10.1103/PhysRevC.67.054319