Level Scheme Study of 91mo: Weak-coupling Approximation in the N=50 Region

The level scheme of 91Mo has been studied using the GALILEO gamma-ray spectrometer at Laboratori Nazionali di Legnaro, INFN. Five transitions together with four levels are identified for the first time by the gamma -gamma coinci-dence measurement, considerably enriching the negative band in 91Mo. 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 91Mo. Being close to N = 50 shell closure, the weak-coupling approximation between the valence g9/2 neutron-hole with the even-even core (92Mo) is discussed in 91Mo.