Measurements of S31 energy levels and reevaluation of the thermonuclear resonant P30(p,γ)S31 reaction rate

C. Wrede, Yale University
J. A. Caggiano, TRIUMF
J. A. Clark, Yale University
C. M. Deibel, Yale University
A. Parikh, Yale University
P. D. Parker, Yale University


By measuring the P31(He3,t)S31, P31(He3,t)S31*(p)P30, and S32(d,t)S31 reactions, the level scheme of S31 has been refined and extended up to Ex=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 S31 levels have been reduced substantially. Spin constraints have been made for 8 proton-unbound levels by measuring 18 triton-proton angular correlations from the P31(He3,t)S31*(p) P30 reaction. Finite proton-decay branching ratios (including discrimination between decays to the ground state and first two excited states of P30) 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 P30+p resonance parameters has been used together with data from previous measurements to calculate the thermonuclear, resonant P30(p,γ)S31 reaction rate over three orders of magnitude in temperature: 0.01