The beta Decay of 32Cl: Precision gamma-Ray Spectroscopy and a Measurement of Isospin-Symmetry Breaking

TL;DR

This study precisely measured gamma-ray yields and ft values for 32Cl decay, revealing significant isospin-symmetry-breaking effects that align with shell-model predictions, thus testing theoretical models of superallowed Fermi decays.

Contribution

The paper provides the most precise gamma yields for 32Cl decay and measures the isospin-symmetry-breaking correction, offering a critical test for nuclear models.

Findings

Gamma yields improved by an order of magnitude

Observation of new gamma transitions up to 11 MeV

Isospin-symmetry-breaking correction measured at 5.4%

Abstract

Background: Models to calculate small isospin-symmetry-breaking effects in superallowed Fermi decays have been placed under scrutiny in recent years. A stringent test of these models is to measure transitions for which the correction is predicted to be large. The decay of 32Cl decay provides such a test case. Purpose: To improve the gamma yields following the beta decay of 32Cl and to determine the ft values of the the beta branches, particularly the one to the isobaric-analogue state in 32S. Method: Reaction-produced and recoil-spectrometer-separated 32Cl is collected in tape and transported to a counting location where beta-gamma coincidences are measured with a precisely-calibrated HPGe detector. Results: The precision on the gamma yields for most of the known beta branches has been improved by about an order of magnitude, and many new transitions have been observed. We have determined 32Cl-decay transition strengths extending up to E_x~11 MeV. The ft value for the decay to the isobaric-analogue state in 32S has been measured. A comparison to a shell-model calculation shows good agreement. CONCLUSIONS: We have experimentally determined the isospin-symmetry-breaking correction to the superallowed transition of this decay to be (\delta_C-\delta_NS)_exp=5.4(9)%, significantly larger than for any other known superallowed Fermi transition. This correction agrees with a shell-model calculation, which yields \delta_C-\delta_NS=4.8(5)%. Our results also provide a way to improve the measured ft values for the beta decay of 32Ar.