Twenty-one [Formula Presented] transitions in [Formula Presented] were identified from [Formula Presented] coincidences in the spontaneous fission of [Formula Presented] starting with the previously known three transitions in [Formula Presented] The level structure of this nucleus is interpreted in part as arising from the weak coupling of the [Formula Presented] neutron hole to the yrast states of the [Formula Presented] core. We have tried to give a quantitative description of the properties of [Formula Presented] by performing a shell-model study in which we assume that [Formula Presented] is a closed core. In this study we have also considered the neighboring isotopes [Formula Presented] The calculated spectra have been compared with the experimental data. 2003 The American Physical Society.