Experimental study of nuclear structure ofMo91at high spin

Abstract

The high spin structure of $^{91}\mathrm{Mo}$ with neutron and proton number close to magicity has been investigated using the $^{63}\mathrm{Cu}(^{31}\mathrm{P},\mathit{xnyp})$ reaction at an incident beam energy of $125\phantom{\rule{0.3em}{0ex}}\text{MeV}$. The level at ${E}_{x}=3811\phantom{\rule{0.3em}{0ex}}\text{keV}$ has been assigned a negative parity based on our polarization measurements. In view of this change, the observed level structure for $^{91}\mathrm{Mo}$ so far does not have any negative parity sequence. More than 30 new transitions were observed and placed in the decay scheme, which has been extended up to spin of $J\ensuremath{\sim}39∕2\ensuremath{\hbar}$ and an excitation energy of ${E}_{x}\ensuremath{\sim}10\phantom{\rule{0.3em}{0ex}}\text{MeV}$. The energy spectrum bears signature of core breaking viz. presence of high energy $({E}_{\ensuremath{\gamma}}\ensuremath{\sim}2\phantom{\rule{0.3em}{0ex}}\text{MeV})$ $\ensuremath{\gamma}$ rays originating due to excitation of nucleons across the shell gaps. The proposed level scheme is compared with large basis spherical shell model calculations. Excitation of protons across $Z=38$ shell dominates the level structure up to moderate spins i.e., $J\ensuremath{\sim}27∕2\ensuremath{\hbar}$. Configurations arising due to excitation of a single $\ensuremath{\nu}{g}_{9∕2}$ across $N=50$ shell gap dominate the higher angular momentum $J\ensuremath{\geqslant}35∕2\ensuremath{\hbar}$ states.