Measurements ofS31energy levels and reevaluation of the thermonuclear resonantP30(p,γ)S31reaction rate

Abstract

By measuring the $^{31}\mathrm{P}(^{3}\mathrm{He},t)^{31}\mathrm{S}$, $^{31}\mathrm{P}(^{3}\mathrm{He},t)^{31}\mathrm{S}{}^{*}(p)^{30}\mathrm{P}$, and $^{32}\mathrm{S}(d,t)^{31}\mathrm{S}$ reactions, the level scheme of $^{31}\mathrm{S}$ has been refined and extended up to ${E}_{x}=9.5$ MeV. A total of 17 new levels, and 5 tentative new levels, have been measured. In addition, 5 tentatively known levels have been confirmed. The uncertainties in the excitation energies of many known $^{31}\mathrm{S}$ levels have been reduced substantially. Spin constraints have been made for 8 proton-unbound levels by measuring 18 triton-proton angular correlations from the $^{31}\mathrm{P}(^{3}\mathrm{He},t)^{31}\mathrm{S}{}^{*}(p)^{30}\mathrm{P}$ reaction. Finite proton-decay branching ratios (including discrimination between decays to the ground state and first two excited states of $^{30}\mathrm{P}$) have been measured for 38 levels, and upper limits have been set for 3 additional levels. The lowest isospin $T=3/2$ level has been observed, and candidates for the second and third $T=3/2$ levels have been identified. The new experimental information on $^{30}\mathrm{P}+p$ resonance parameters has been used together with data from previous measurements to calculate the thermonuclear, resonant $^{30}\mathrm{P}(p,\ensuremath{\gamma})^{31}\mathrm{S}$ reaction rate over three orders of magnitude in temperature: $0.01<T<10$ GK. Good agreement is found with estimates based on Hauser-Feshbach statistical models over the range $0.08<T<10$ GK, but differences are found with rates previously estimated using the experimental information at hand.