LEVEL STRUCTURE OF 30S AND THE 29P(p, gamma)30S THERMONUCLEAR REACTION RATE

Abstract

<p>In order to determine the parent stellar sites for the presolar grains of potential nova origin, it is crucial to know the rates of the thermonuclear reactions which affect the Si production and destruction in novae. One such reaction is the ²⁹P(p, gamma)³⁰S. This reaction also influences type I X-ray bursts. The energy generation and nucleosynthesis in the burst, along with its duration and light-curve structure, are very sensitive to the reaction flow through a few waiting-point nuclei along the rp- and ap-process paths. In particular, network calculations show that the waiting-point nucleus ³⁰S (t_1/2 = 1175.9(17) ms) is critical.</p> <p>The structure of proton-unbound ³⁰S states strongly determines the thermonuclear ²⁹P(p, gamma)³⁰S reaction rate at temperatures characteristic of explosive hydrogen burning in classical novae and type I X-ray bursts (0.1 ≤ T ≤ 1.3 GK). Specifically, the rate had been previously predicted to be dominated by two low-lying, unobserved, J^pi= 3⁺and 2⁺ levels in the E_x = 4.7 to 4.8 MeV region.</p> <p>The 3⁺resonance was observed a few years ago via a ³²S(p, t)³⁰S measurement. However, the 2⁺resonance remained unobserved. To search for it, we have performed a higher energy resolution charged-particle spectroscopy and an in-beam gamma-ray spectroscopy to investigate the level structure of ³⁰S above the proton threshold via the ³²S(p, t)³⁰S and ²⁸Si(³He, n-gamma)³⁰S reactions, respectively.</p> <p>In this work we provide a description of the experimental setup, data analysis and results of both experiments. Moreover, we have calculated the ²⁹P(p, gamma)³⁰S reaction rate via the state-of-the-art Monte Carlo technique, and have investigated the impact of this updated rate on the abundances of elements synthesized in novae, including those of silicon isotopes.</p>