Investigation of level structure in the semimagic nucleus 91Nb and systematics of nuclear structure characteristics near A=90

We report the new level scheme of the 91Nb nucleus established by the reactions 82Se(14N, 5n) 91Nb and 76Ge(19F, 4n) 91Nb. Thirty new transitions with energies up to about 12 MeV are assigned to the 91Nb nucleus and placed in the proposed level scheme. The excited levels are well reproduced by shell-model calculations with the GWBXG effective interaction. The obtained results, which conform to the most experimental data well, manifest that the high spins are construed as the proton excitations from 1p3/2, 0 f5/2, and 1p1/2 orbitals, to the 0g9/2 orbital with the breakup of the Z = 38 (40) core, as well as neutron excitations from the 0g9/2 orbital to the 1d5/2 or 0g7/2 orbital with the breakup of the N = 50 core.