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

Abstract.

Recent experimental data about the ³⁰P(p,$\gamma$) reaction have been reported, where a list of confirmed ³¹S excited states within 500 keV of the ³⁰P(p,$\gamma$)³¹S threshold at $E_{x} = 6131$ keV and their properties were studied. Definitive constraints on $J^{\pi}$ 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 $(0+1)\hbar\omega$ PSDPF interaction to calculate the excitation energy spectrum of mass 31 ( ³¹S - ³¹P 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 ³¹P spectrum up to 7000 keV.