Superdeformation in ${}^{68}\mathrm{Zn}$: Evidence for a New, Neutron-Rich Island of Superdeformation in $\mathit{A}\sim 70$ Nuclei

A superdeformed rotational structure is reported in the stable nucleus ${}^{68}\mathrm{Zn}$. It has a transition quadrupole moment ( $Q_t$) of ${2.5}_{-0.4\mathrm{}}^{+0.7\mathrm{}}$ $e$ b ( ${\beta }_2\approx 0.4$), as measured by the residual Doppler shift method. Theoretical calculations suggest that two different configurations are possible candidates for this band. One is built without $h_{11/2}$ neutrons, as seen in superdeformed bands in the $A\sim 60$ region, while the other involves one $h_{11/2}$ neutron in analogy with superdeformed bands in the $A\sim 80$ region. The second of these candidate configurations is preferred, thus establishing a new, neutron-rich (relative to the line of $\beta$ stability) region of superdeformation with $Z\sim 30$ and $N\sim 38$.