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.

• Received 14 April 2005

DOI:https://doi.org/10.1103/PhysRevC.71.064312