Detailed study of the decay Cl31(βγ)S31

Abstract

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.

Toward complete spectroscopy using β decay: The example of Cl32(βγ)S32Aboud1, Bennett2, Wrede3 et al. 2018Phys. Rev. CSelf Cite2020View full textAdd to dashboardCite

“…The present measurement is part of a recent program of high-resolution β + delayed γ decay measurements of proton-rich sd-shell nuclides [5][6][7][19][20][21][22][23][24][25]. The data set discussed in the present work was obtained over the course of approximately six hours at the National Superconducting Cyclotron Laboratory (NSCL) as calibration data for the analysis of an experiment designed to study the β decay of 31 Cl [6,19,20].…”

“…The 32 Cl production mechanism and experimental procedure are similar to those described in Refs. [6,19] for 31 Cl. Briefly, a primary beam of 150 MeV/u, 75-pnA 36 Ar was produced using the Coupled Cyclotron Facility at the NSCL and impinged upon a 1627-mg/cm 2 Be transmission target to generate a cocktail beam via projectile fragmentation that included 32 Cl.…”

“…The intensities were calibrated internally with respect to the standard intensities found in Melconian et al [15] We built a relative efficiency curve using 152 Eu source data for E γ < 1.4 MeV and the normalized 32 Cl(β + γ) 32 S photopeaks for 1.5 < E γ < 7.2 MeV [6,19]. The relative efficiency curve was arbitrarily normalized to unity at 4281 keV and fit with the function:…”

“…Their measurement demonstrated the largest isospin symmetry breaking effect in a superallowed Fermi β + decay, providing an important test of nuclear structure corrections that are used in searches for new physics based on β + decay [1,17]. Mixing of a similar magnitude has been observed in 31 S using the β decay of another chlorine isotope, 31 Cl, [6] and both cases have been explained in terms of T = 1, J = 2 isospin non-conserving interactions related to the s 1/2 orbit [18]. Despite the relatively high sensitivity of their experiment, Melconian et al were limited by a lack of statistics and acquisition of data at high γ-ray energies, and their decay scheme was consequently supplemented by including unobserved transitions adopted from experimental nuclear reaction data in the ENSDF database [8] and shell-model calculations.…”

“…Experimental studies of β + decay in the sd shell are sensitive probes of nuclear structure that is applicable to searches for physics beyond the standard model of the electroweak interaction [1] and to the study of nucleosynthesis and energy generation in astrophysical hydrogen and helium burning environments [2][3][4][5][6][7]. In the past, the constraints imposed by β decay selection rules, radioactive beam intensities, and radiation detection efficiencies have mostly limited the utility of β decay spectroscopy to the study of the states whose population is allowed by the selection rules, except in special cases where only forbidden transitions are energetically accessible.…”