Shell-model study of 31S at excitations relevant to the thermonuclear 30P(p, γ)31S reaction rate

Recent experimental data about the P-30(p, gamma) reaction have been reported, where a list of confirmed S-31 excited states within 500 keV of the P-30(p, gamma) S-31 threshold at E-x = 6131 keV and their properties were studied. Definitive constraints on J p are only given for two levels; the other ones are either tentative (five states) or undefined (six states). In order to confirm the proposed spin/parity assignments and to determine the unknown ones a comparison with shell-model calculations is crucial. We have performed a shell-model calculation using the (0 + 1)hw. PSDPF interaction to calculate the excitation energy spectrum of mass 31 (S-31-P-31) up to 7000 keV. Between 6100 and 6700 keV, an excitation energy region of astrophysical interest, we obtain a set of negative-parity states that are good candidates for the observed ones. A complete spectrum of positive-and negative-parity states can now be proposed based also on a comparison with the P-31 spectrum up to 7000 keV.