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International audience; The P30(p,γ)S31 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 Cl31 β-delayed proton decay through the key Jπ=3/2+, 260-keV resonance. The intensity Iβp260=8.3-0.9+1.2×10-6 represents the weakest β-delayed, charged-particle emission ever measured below 400 keV, resulting in a proton branching ratio of Γp/Γ=2.5-0.3+0.4×10-4. By combining this measurement with shell-model calculations for Γγ and past work on other resonances, the total P30(p,γ)S31 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 Si30:Si28 excesses in presolar nova grains and the calibration of nuclear thermometers.

The 30P(p,γ)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 β-delayed proton decay through the key Jπ=3/2+, 260-keV resonance. The intensity I260βp=8.3+1.2−0.9×10−6 represents the weakest β-delayed, charged-particle emission ever measured below 400 keV, resulting in a proton branching ratio of Γp/Γ=2.5+0.4−0.3×10−4. By combining this measurement with shell-model calculations for Γγ and past work on other resonances, the total 30P(p,γ)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., Research at NSCL was funded by the National Science Foundation under Grants No. PHY-1913554, No. PHY1102511, No. PHY-1565546, No. PHY-2110365, No. PHY-2011890, as well as by the Department of Energy Office of Science under Award No. DESC0016052. We acknowledge support from the Natural Sciences and Engineering Research Council of Canada (NSERC), as well as the Spanish MINECO Grant No. AYA2017-86274-P, the E.U. FEDER funds, the AGAUR/Generalitat de Catalunya Grant No. SGR-661/ 2017, and the EU Horizon 2020 Grant No. 101008324 ChETEC-INFRA. This article also benefited from discussions within the ChETEC COST Action (CA16117). Additional funding sources include Korean NRF Grants No. 2020R1A2C1005981 and No. 2016R1A5A1013277.

$\beta$-decay spectroscopy provides valuable information on exotic nuclei and a stringent test for nuclear theories beyond the stability line. To search for new $\beta$-delayed protons and $\gamma$ rays of $^{25}$Si to investigate the properties of $^{25}$Al excited states. $^{25}$Si $\beta$ decays were measured by using the Gaseous Detector with Germanium Tagging system at the National Superconducting Cyclotron Laboratory. The protons and $\gamma$ rays emitted in the decay were detected simultaneously. A Monte Carlo method was used to model the Doppler broadening of $^{24}$Mg $\gamma$-ray lines caused by nuclear recoil from proton emission. Shell-model calculations using two newly developed universal \textit{sd}-shell Hamiltonians, USDC and USDI, were performed. The most precise $^{25}$Si half-life to date has been determined. A new proton branch at 724(4)~keV and new proton-$\gamma$-ray coincidences have been identified. Three $^{24}$Mg $\gamma$-ray lines and eight $^{25}$Al $\gamma$-ray lines are observed for the first time in $^{25}$Si decay. The first measurement of the $^{25}$Si $\beta$-delayed $\gamma$ ray intensities through the $^{25}$Al unbound states is reported. All the bound states of $^{25}$Al are observed to be populated in the $\beta$ decay of $^{25}$Si. Several inconsistencies between the previous measurements have been resolved, and new information on the $^{25}$Al level scheme is provided. An enhanced decay scheme has been constructed and compared to the mirror decay of $^{25}$Na and the shell-model calculations. The measured excitation energies, $\gamma$-ray and proton branchings, log~$ft$ values, and Gamow-Teller transition strengths for the states of $^{25}$Al populated in the $\beta$ decay of $^{25}$Si are in good agreement with the shell-model calculations, offering gratifyingly consistent insights into the fine nuclear structure of $^{25}$Al.

The radionuclide 22Na is a target of γ-ray astronomy searches, predicted to be produced during thermonuclear runaways driving classical novae. The 22Na(p,γ)23Mg reaction is the main destruction channel of 22Na during a nova, hence, its rate is needed to accurately predict the 22Na yield. However, experimental determinations of the resonance strengths have led to inconsistent results. In this Rapid Communication, we report a measurement of the branching ratios of the 23Alβ-delayed protons as a probe of the key 204-keV (center-of-mass) 22Na(p,γ)23Mg resonance strength. We report a factor of 5 lower branching ratio compared to the most recent literature value. The variation in 22Na yield due to nuclear data inconsistencies was assessed using a series of hydrodynamic nova outburst simulations and has increased to a factor of 3.8, corresponding to a factor of ≈2 uncertainty in the maximum detectability distance. This is the first reported scientific measurement using the Gaseous Detector with Germanium Tagging system., This work was supported by the U.S. National Science Foundation under Grants No. PHY-1102511, No. PHY-1565546, and No. PHY-1913554, and the U.S. Department of Energy, Office of Science, under Award No. DE-SC0016052. We also acknowledge support by the Spanish MINECO Grant No. AYA2017-86274-P by the E.U. FEDER funds and by the AGAUR/Generalitat de Catalunya Grant No. SGR-661/2017. T