Isospin Mixing Reveals $^{30}$P($p,\gamma$)$^{31}$S Resonance Influencing Nova Nucleosynthesis

TL;DR

This study identifies a key resonance in $^{31}$S through isospin mixing, providing crucial data to better constrain the $^{30}$P($p, extgamma$)$^{31}$S reaction rate impacting nova nucleosynthesis models.

Contribution

The paper experimentally observes a specific $^{31}$S state and determines its spin, parity, and resonance energy, clarifying its role in nova nucleosynthesis.

Findings

Identified a $^{31}$S state at 6390 keV with $J^ ext{pi} = 3/2^+$.

Determined the resonance energy at 259.3 keV within the nova Gamow window.

Confirmed isospin mixing with the isobaric analog state.

Abstract

The thermonuclear $^{30}$P($p,\gamma$)$^{31}$S reaction rate is critical for modeling the final elemental and isotopic abundances of ONe nova nucleosynthesis, which affect the calibration of proposed nova thermometers and the identification of presolar nova grains, respectively. Unfortunately, the rate of this reaction is essentially unconstrained experimentally, because the strengths of key $^{31}$S proton capture resonance states are not known, largely due to uncertainties in their spins and parities. Using the $\beta$ decay of $^{31}$Cl, we have observed the $\beta$-delayed $\gamma$ decay of a $^{31}$S state at $E_x = 6390.2(7)$ keV, with a $^{30}$P($p,\gamma$)$^{31}$S resonance energy of $E_r = 259.3(8)$ keV, in the middle of the $^{30}$P($p,\gamma$)$^{31}$S Gamow window for peak nova temperatures. This state exhibits isospin mixing with the nearby isobaric analog state (IAS) at $E_x = 6279.0(6)$ keV, giving it an unambiguous spin and parity of $3/2^+$ and making it an important $l = 0$ resonance for proton capture on $^{30}$P.