Investigation of level structure in the semimagic nucleus Nb91 and systematics of nuclear structure characteristics near A=90

We report the new level scheme of the $^{91}\mathrm{Nb}$ nucleus established by the reactions $^{82}\mathrm{Se}(^{14}\mathrm{N},\phantom{\rule{4pt}{0ex}}5n)^{91}\mathrm{Nb}$ and $^{76}\mathrm{Ge}(^{19}\mathrm{F},\phantom{\rule{4pt}{0ex}}4n)^{91}\mathrm{Nb}$. Thirty new transitions with energies up to about 12 MeV are assigned to the $^{91}\mathrm{Nb}$ 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 $1{p}_{3/2}$, $0{f}_{5/2}$, and $1{p}_{1/2}$ orbitals, to the $0{g}_{9/2}$ orbital with the breakup of the $Z=38$ (40) core, as well as neutron excitations from the $0{g}_{9/2}$ orbital to the $1{d}_{5/2}$ or $0{g}_{7/2}$ orbital with the breakup of the $N=50$ core.