Isospin-Forbidden Compound Nuclear Resonances inAl25andP29

Abstract

The analogs of the ground state and first excited state of ${}_{}{}^{25}{}_{}{}^{}\mathrm{Na}$ and ${}_{}{}^{29}{}_{}{}^{}\mathrm{Al}$ have been studied as compound resonances in ${}_{}{}^{25}{}_{}{}^{}\mathrm{Al}$ and ${}_{}{}^{29}{}_{}{}^{}\mathrm{P}$, respectively, formed by scattering protons from ${}_{}{}^{24}{}_{}{}^{}\mathrm{Mg}$ and ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$ targets. The accurate excitation energies obtained for these resonances, which are in excellent agreement with their locations available from delayed-proton, ($p,t$), and ($p,\gamma$) experiments, were used to predict the masses of ${}_{}{}^{25}{}_{}{}^{}\mathrm{Si}$ and ${}_{}{}^{29}{}_{}{}^{}\mathrm{S}$ from the isobaric-multiplet mass formula, and to calculate Coulomb-energy differences between the members of these isospin quartets. Total widths (<300 eV) and partial proton widths were extracted for the sharp isospin-forbidden $T=\frac{3}{2}$ resonances and compared with the widths of several new $T=\frac{1}{2}$ resonances in ${}_{}{}^{25}{}_{}{}^{}\mathrm{Al}$ and ${}_{}{}^{29}{}_{}{}^{}\mathrm{P}$ lying in the same region of excitation (7.5 to 10.0 MeV). Shifts are observed between the locations of corresponding analog states in the parent and $T_z=-\frac{1}{2}$ nuclei.