High-spin level structure of the semi-magic nucleusNb91

The high-spin level structure of the semi-magic nucleus $^{91}\mathrm{Nb}$ has been investigated via the ${}^{82}$Se(${}^{14}$N,$5n$)$^{91}\mathrm{Nb}$ reaction at a beam energy of 60 MeV. Based on these experimental results, a new level scheme is established that modifies and extends earlier schemes. Shell-model calculations have been carried out to interpret the level structure of $^{91}\mathrm{Nb}$. The calculated results show that the inclusion of neutron particle-hole excitation across the $N=50$ shell gap is essential to adequately describe states above $I=(21/2\phantom{\rule{0.16em}{0ex}}--\phantom{\rule{0.16em}{0ex}}23/2)\ensuremath{\hbar}$, with excitation energies above $\ensuremath{\sim}$6.0 MeV.