Level scheme study of Mo 91: Weak-coupling approximation in the N=50 region

The level scheme of Mo91 has been studied using the GALILEO γ-ray spectrometer at Laboratori Nazionali di Legnaro, INFN. Five transitions together with four levels are identified for the first time by the γ-γ coincidence measurement, considerably enriching the negative band in Mo91. The discrepancy in the previous parity assignments for the states higher than 3807.5 keV has been clarified with the help of new experimental results. A shell-model calculation employing the JUN45 interaction is performed in order to get a further understanding of the level structure of Mo91. Being close to N=50 shell closure, the weak-coupling approximation between the valence g9/2 neutron-hole with the even-even core (Mo92) is discussed in Mo91.