Levels ofRb91andSr91fed in the decays ofKr91andRb91

Level schemes for ${}_{}{}^{91}{}_{}{}^{}\mathrm{Rb}$ and ${}_{}{}^{91}{}_{}{}^{}\mathrm{Sr}$ are proposed based on the study of the $\beta$ decay of ${}_{}{}^{91}{}_{}{}^{}\mathrm{Kr}$ and ${}_{}{}^{91}{}_{}{}^{}\mathrm{Rb}$, respectively. The samples were obtained using on-line mass-separation techniques applied to ${}_{}{}^{235}{}_{}{}^{}\mathrm{U}$ fission products. $\gamma$-, $\beta$-, and x-ray singles spectra, as well as ($\gamma ,\gamma$) and ($\beta ,\gamma$) coincidence spectra, were taken with Ge(Li) and Si(Li) detectors. Internal-conversion coefficients were determined for several transitions and the half-lives for the first two levels in ${}_{}{}^{91}{}_{}{}^{}\mathrm{Rb}$ and ${}_{}{}^{91}{}_{}{}^{}\mathrm{Sr}$ were measured. In view of the observed parity change between low-lying excited states and the ground state in ${}_{}{}^{91}{}_{}{}^{}\mathrm{Rb}$ the possibility of deformations to explain this level structure is discussed.