Investigation of $^{31}$P levels near the proton threshold by Nuclear Resonance Fluorescence and the impact on the $^{30}$Si(p,$\gamma$)$^{31}$P thermonuclear rate

TL;DR

This study used Nuclear Resonance Fluorescence to precisely measure $^{31}$P nuclear states near the proton threshold, refining the $^{30}$Si(p,$ extgamma$)$^{31}$P reaction rate crucial for stellar nucleosynthesis models.

Contribution

It provides the first unambiguous spin-parity assignments for key resonances and updates the thermonuclear reaction rate with implications for astrophysical nucleosynthesis.

Findings

Revised $^{30}$Si(p,$ extgamma$)$^{31}$P rate is lower below 200 MK.

Identified two previously unobserved resonances at 18.7 keV and 50.5 keV.

First angular correlation analysis for these states.

Abstract

We investigated the nuclear structure of $^{31}$P near the proton threshold using Nuclear Resonance Fluorescence (NRF) to refine the properties of key resonances in the $^{30}$Si(p,$\gamma$)$^{31}$P reaction, which is critical for nucleosynthesis in stellar environments. Excitation energies and spin-parities were determined for several states, including two unobserved resonances at $E_r$ $=$ $18.7$~keV and $E_r$ $=$ $50.5$~keV. The angular correlation analysis enabled the first unambiguous determination of the orbital angular momentum transfer for these states. These results provide a significant update to the $^{30}$Si(p,$\gamma$)$^{31}$P thermonuclear reaction rate, with direct implications for models of nucleosynthesis in globular clusters and other astrophysical sites. The revised rate is substantially lower than previous estimates at temperatures below $200$~MK, affecting predictions for silicon isotopic abundances in stellar environments. Our work demonstrates the power of NRF in constraining nuclear properties, and provides a framework for future studies of low-energy resonances relevant to astrophysical reaction rates.