High-spin states inN=50Br85andRb87nuclei

Abstract

The level structures of the $N=50$ $^{85}\mathrm{Br}$ and $^{87}\mathrm{Rb}$ isotopes have been studied in the fission of the compound system formed in three different heavy-ion-induced reactions. In $^{87}\mathrm{Rb}$ many states above the previously known 9/2${}^{+}$ isomer have been established. The coupling of the odd proton occupying the ${g}_{9/2}$ orbital to the yrast states in the $^{86}\mathrm{Kr}$ core can account for the first excited states above the isomer in $^{87}\mathrm{Rb}$. A comparison with the first excited states above the 9/2${}^{+}$ state in $^{85}\mathrm{Kr}$ and $^{89}\mathrm{Y}$ reveals similarities in the coupling. At higher excitations similar behavior to $^{89}\mathrm{Y}$ is observed, indicating a possible presence of neutron-core excitations. In $^{85}\mathrm{Br}$ several states up to ~5 MeV excitation energy have been established. Two states at ~2 MeV excitation energy are candidates for the 9/2${}^{+}$ state originating from the odd proton occupying the ${g}_{9/2}$ orbital. The experimental results for both isotopes are compared with predictions of the shell model.