M. Cortesi,1 B. Glassman,1,2 M. R. Hall ?,8,1,2,10,8,13?,10?,1,2 and 1,2 1Department of Physics and Astronomy, Michigan State University, East Lansing, Michigan 48824, USA

(Received 9 June 2021; revised 14 January 2022; accepted 4 April 2022; published 3 May 2022) The 30P(p, ?? )31S reaction plays an important role in understanding the nucleosynthesis of A > 30 nuclides in oxygen-neon novae. The Gaseous Detector with Germanium Tagging was used to measure 31Cl ??-delayed proton decay through the key J?? = 3/2+, 260-keV resonance. The intensity I260 ???0.9 ?? 10???6 represents the weakest ??-delayed, charged-particle emission ever measured below 400 keV, resulting in a proton branching ratio of ??p/?? = 2.5+0.4 model calculations for ???? and past work on other resonances, the total 30P(p, ?? )31S rate has been determined with reduced uncertainty. The new rate has been used in hydrodynamic simulations to model the composition of nova ejecta, leading to a concrete prediction of 30Si:28Si excesses in presolar nova grains and the calibration of nuclear thermometers.