Study ofNb93Levels with theMo96(p,α)Nb93Reaction

Levels of ${}_{}{}^{93}{}_{}{}^{}\mathrm{Nb}$ have been studied with the ${}_{}{}^{96}{}_{}{}^{}\mathrm{Mo}(p,\alpha )$ reaction at 15-MeV incident energy. Angular distributions for transitions to a dozen prominent levels below 2 MeV have been measured with 30- to 40-keV experimental resolution over ${15}^{\circ }\le {\theta }_L\le {150}^{\circ }$, and they have been compared with distorted-wave Born-approximation (DWBA) calculations. Angular distributions for $p-{}_{}{}^{96}{}_{}{}^{}\mathrm{Mo}$ and $\alpha -{}_{}{}^{93}{}_{}{}^{}\mathrm{Nb}$ elastic scattering have also been measured, and proton and $\alpha$-optical-model potential parameter sets have been determined by a search procedure. Of the three sets of $\alpha$-potential parameters, the one which best reproduced the measured ($p,\alpha$) angular distributions of known low-lying levels in ${}_{}{}^{93}{}_{}{}^{}\mathrm{Nb}$ was chosen as the standard set for the rest of the ($p,\alpha$) calculations. The conventional triton-cluster form factor was used exclusively for the ($p,\alpha$) DWBA calculations which lead to $J^{\pi }$ assignments. A semimicroscopic form factor was used in a few test cases in order to check the sensitivity of calculations to the choice of form factor. Reliable $J^{\pi }$ assignments have been made for levels below 1.5 MeV based on the $j$ dependence for $l=1(p,\alpha )$ transfers, as well as for higher angular momentum transfers observed in the present work; and they are in excellent agreement with those determined from recent Coulomb-excitation and ${}_{}{}^{90}{}_{}{}^{}\mathrm{Zr}(\alpha ,p\gamma )$ works. Dominant three-nucleon shell-model configurations to which the levels of interest belong have been proposed.