Evidence for Deformed Ground States in Light Kr Isotopes

Abstract

The levels in ${}_{}{}^{74,76}{}_{}{}^{}\mathrm{Kr}$ were studied with in-beam $\gamma$-spectroscopy techniques and the ${\beta }^{+}$ decay of ${}_{}{}^{76}{}_{}{}^{}\mathrm{Rb}$. The energies of the $2_1^{+}$ states in ${}_{}{}^{74,76}{}_{}{}^{}\mathrm{Kr}$ deviate from smooth behavior compared with the higher spin levels. The yrast cascade $B\left(E2\mathrm{}\right)\mathrm{}$'s are highly collective. The ${}_{}{}^{74,76}{}_{}{}^{}\mathrm{Kr}$ ground states have unusually large deformation. The origin of this deformation and of shape coexistence in this region is described in terms of the protons driving the deformation.