β decay of 32Cl: Precision γ-ray spectroscopy and a measurement of isospin-symmetry breaking

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 Cl-32 decay provides such a test case. Purpose: The purpose of this paper is to improve the gamma yields following the beta decay of Cl-32 and to determine the f t values of the the beta branches, particularly the one to the isobaric-analog state in S-32. Method: Reaction-produced and recoil-spectrometer-separated Cl-32 is collected in a tape and transported to a counting location where beta-gamma coincidences are measured with a precisely calibrated high-purity germanium 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 Cl-32-decay transition strengths extending up to E-x similar to 11 MeV. The f t value for the decay to the isobaric-analog state in S-32 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 f t values for the beta decay of Ar-32.