Experimental study of the level structure in ${}_{90}\mathrm{Nb}$ and systematics of level structure characteristics near $A=90$

In beam $\gamma$-ray spectroscopic investigations of the ${}_{90}\mathrm{Nb}$ nucleus have been explored by employing the ${}_{76}\mathrm{Ge}({}_{19}F,5n){}_{90}\mathrm{Nb}$ reaction. Twenty-eight new transitions belonging to ${}_{90}\mathrm{Nb}$ have been identified and placed in the proposed level scheme through the analysis of $\gamma \text{−}\gamma$ coincidence spectra. Shell model calculations have been performed in the restricted $\pi (p_{3/2},f_{5/2},p_{1/2},g_{9/2})\otimes \nu (p_{1/2},g_{9/2},d_{5/2},g_{7/2})$ configuration space, and compared to the new level scheme. According to the calculations, the newly observed 2614.6 keV $\gamma$ ray depopulating the $\left({15}_3^{+}\right)$ level at 4421.2 keV is explicated as the breakup of the $N=50$ neutron closed shell, while the $\gamma$ ray with 2774.0 keV feeding the $\left({13}_1^{-}\right)$ level at 2812.9 keV is interpreted as protons excitation across the $Z=38$ subshell.