Isospin mixing reveals 30P(p, γ)31S resonance influencing nova nucleosynthesis

Here, the thermonuclear 30P(p, γ)31S 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 31S proton capture resonance states are not known, largely due to uncertainties in their spins and parities. Using the β decay of 31Cl, we have observed the β-delayed γ decay of a 31S state at Ex = 6390.2(7) keV, with a 30P(p, γ)31S resonance energy of Er = 259.3(8) keV, in the middle of the 30P(p, γ)31S Gamow window for peak nova temperatures. This state exhibits isospin mixing with the nearby isobaric analog state at Ex = 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 30P.