Unbound States of 32Cl Relevant for Novae

Abstract

The 31S(p,g )32Cl proton–capture reaction is expected to be the dominant breakout pathway of the SiP cycle, which is important for understanding nucleosynthesis in some novae [1]. At novae temperatures, the 31S(p,g )32Cl reaction rate is dominated by 31S+p resonances. Discrepancies in the 32Cl resonance energies were reported in previous measurements [1, 2]. We used the 32S(3He,t)32Cl charge–exchange reaction to produce unbound states in 32Cl and determine their excitation energies by detecting tritons at the focal plane of the Enge Spectrograph at the Yale University’s Wright Nuclear Structure Laboratory. Proton branching ratios were determined by detecting the decay protons coming from the residual 32Cl states using a silicon array in the spectrometer’s target chamber. The improved energy values of excited levels in 32Cl and measurements of the proton-branching ratios should significantly improve our understanding of the 31S(p,g )32Cl reaction rate.