Observation of the ${\left(g_{\frac{9}{2}}\right)}^2$ Multiplet in ${\mathrm{Nb}}^{90}$ via the (${\mathrm{He}}^3$, $t$) Reaction

Results are reported for angular distributions of the reaction ${\mathrm{Zr}}^{90}({\mathrm{He}}^3, t){\mathrm{Nb}}^{90}$ at 21 MeV. It is found that for targets in the $f_{\frac{7}{2}}$ shell this reaction favors specific final states in which a neutron is replaced by a proton in the same shell-model orbit, coupled to any allowed angular momentum. The angular distributions differ in a systematic way depending on the spin of the final state. The nine states of the $T_{<}$ ${\left(g_{\frac{9}{2}}\right)}^2$ multiplet are tentatively identified. A multipole decomposition leads to coefficients very similar to those of the ${\left(f_{\frac{7}{2}}\right)}^2$ multiplet, showing an enhanced quadrupole coefficient.