Investigation of Excited States of ${\mathrm{P}}^{31}$ with the ${\mathrm{Si}}^{30}(p, \gamma ){\mathrm{P}}^{31}$ Reaction

Some previously unknown properties of excited states of ${\mathrm{P}}^{31}$ were investigated by studying the $\gamma$ rays from the reaction ${\mathrm{Si}}^{30}(p, \gamma ){\mathrm{P}}^{31}$. A coincidence spectrum taken at the resonance proton energy $E_p=1177\mathrm{}$ keV reduced the maximum possible branching ratio of the decay of the 2.23-MeV level via the 1.27-MeV level to 0.8%. Spectra taken at the $E_p=1694\mathrm{}$-keV resonance yielded decay schemes for the unbound level at 8.93 MeV and the bound levels at 4.78, 5.12, and 5.66 MeV. Angular-correlation measurements at the same resonance led to the assignment of $J^{\pi }=\frac{5}{2^{+}}$ to the 4.78-MeV level. $\gamma$-ray linear-polarization measurements at the resonances at $E_p=1204, 1322, 1509, \mathrm{and} 2187$ keV verified experimentally the even-parity assignments for the levels at 3.29, 3.41, 3.51, and 4.26 MeV and the virtual levels at 8.45 and 8.75 MeV. By comparison of the polarization results with results of earlier triple-correlation measurements, the unique values $\delta =-0.41\mathrm{}\pm 0.03$ and $\delta =-0.32\mathrm{}\pm 0.04$ were obtained for the $M1-E2\mathrm{}$ mixing ratios of the 3.51 → 0 and 4.26 → 0 transitions, respectively.