Medium-spin states in135Cs

Abstract

Limited information is currently known on medium- and higher-spin states for ${}^{135}$Cs, a neutron-rich nucleus amenable to shell-model calculations due to its proximity to the shell closures in ${}^{132}$Sn. In order to extend the level structure of ${}^{135}$Cs to higher excitations, this nucleus was studied via prompt $\ensuremath{\gamma}$-ray spectroscopy of fragments following the fission of the compound nucleus ${}^{226}$Th formed in the ${}^{18}$O (91 MeV) $+$ ${}^{208}$Pb fusion-fission reaction. Medium-spin states up to spin (23/2) and $\ensuremath{\sim}$3.3 MeV excitation energy have been established. The observed states were compared with those in the neighboring $N=82$${}^{137}$Cs nucleus, as well as with states in the neighboring $N=80$ isotones. The coupling of the odd proton occupying the ${g}_{7/2}$ orbital to the yrast states in the ${}^{134}$Xe and ${}^{136}$Ba cores could account for the lower excited states of ${}^{135}$Cs. The experimental results are compared with predictions from shell-model calculations.