Background: 31 Cl is a neutron-deficient isotope with a half-life of T 1/2 = 190(1) ms. The nuclear structure of its daughter, 31 S, is important for the determination of the thermonuclear 30 P(p, γ) 31 S reaction rate, which affects the final isotopic abundances of the ejecta from classical oxygen-neon novae. Purpose: Determine the β feedings, γ-decay branchings, and excitation energies of states populated in 31 S and create a comprehensive decay scheme for comparison with predicitions based on the shell model. Methods: Using a 31 Cl rare istope beam implanted into a plastic scintillator and an array of high-purity Ge detectors, γ rays from the 31 Cl(βγ) 31 S decay sequence were measured. Shell-model calculations using the USDB and the recently-developed USDE interactions were performed for comparison. Results: A 31 Cl β-decay scheme was constructed from the experimental data and compared to the USDB and USDE shell-model calculations based on the β feeding and γ-decay branches of each observed state. 33 new γ-ray transitions and ten new β decay branches were observed. The β feeding and γ-decay branches of each observed state were compared to those from the USDB and USDE shell-model calculations. For every allowed transition predicted by the USD calculations up to an excitation energy of 6.4 MeV in 31 S, an analogous transition was found in the experimental data, enabling a one-to-one comparison with the shell model. Using these identifications, spin and parity arguments were made for observed states. Conclusions: The new 31 Cl γ-decay scheme presented in this work is the most complete and precise one for this nucleus constructed to date, incorporating over an order of magnitude higher statistics than previous work on 31 Cl β-delayed γ decay. Of particular interest is the discovery of a 6390-keV state that mixes with the isobaric analog state and affects the 30 P(p, γ) 31 S reaction rate. Other states observed in the decay are not expected to strongly affect the 30 P(p, γ) 31 S reaction rate, but the comprehensive comparison to the shell model helps to clarify spin and parity assignments of resonances that might affect the rate.

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Background: The Doppler broadening of γ-ray peaks due to nuclear recoil from β-delayed nucleon emission can be used to measure the energies of the nucleons. This method has never been tested using β-delayed proton emission or applied to a recoil heavier than A = 10. Purpose: To test and apply this Doppler broadening method using γ-ray peaks from the 26 P(βpγ) 25 Al decay sequence. Methods: A fast beam of 26 P was implanted into a planar Ge detector, which was used as a 26 P β-decay trigger. The SeGA array of high-purity Ge detectors was used to detect γ rays from the 26 P(βpγ) 25 Al decay sequence. Results: Radiative Doppler broadening in β-delayed proton-γ decay was observed for the first time. The Doppler broadening analysis method was verified using the 1613 keV γ-ray line for which the proton energies were previously known. The 1776 keV γ ray de-exciting the 2720 keV 25 Al level was observed in 26 P(βpγ) 25 Al decay for the first time and used to determine that the center-of-mass energy of the proton emission feeding the 2720-keV level is 5.1 ± 1.0 (stat.) ± 0.6 (syst.) MeV, corresponding to a 26 Si excitation energy of 13.3 ± 1.0 (stat.) ± 0.7 (syst.) MeV for the proton-emitting level. Conclusions: The Doppler broadening method has been demonstrated to provide practical measurements of the energies for β-delayed nucleon emissions populating excited states of nuclear recoils at least as heavy as A = 25.

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