Evidence of shell effects in the excitation function of 0.136-MeV isomeric state populated in the 93Nb(n,2n)92Nbm reaction

Calculation for the excitation function of 0.136-MeV (2+) isomeric state in 92Nb has been carried out using Hauser-Feshbach and pre-equilibrium nuclear reaction models in 10-20 MeV energy range. A satisfactory agreement between the calculation and measurements requires the suppression of contribution from the negative-parity doublet consisting of the 0.226-MeV (2-) and 0.390-MeV (3-) states in 92Nb. This can be explained on the basis of highly retarded gamma transitions of higher energy states to the negative-parity doublet on account of its different shell model configuration compared to the shell model configuration of positive-parity states