Toward complete spectroscopy using β decay: The example of Cl32(βγ)S32

Background: Cl32 is a neutron-deficient isotope with a β-decay half-life of 298 ms and a spin and parity of Jπ=1+. Previous measurements of Cl32 β-delayed γ rays have yielded a β-decay scheme with twelve β-decay transitions, contributing to studies of nuclear structure and fundamental symmetries. Those experiments have been limited to the observation of S32 states with Jπ=0+,1+,2+. Purpose: Our goal is to search for new β-delayed γ rays and β-decay transitions of Cl32 to S32. Methods: A measurement of Cl32 β-delayed γ decay has been performed using the Clovershare array of high-purity germanium detectors at the National Superconducting Cyclotron Laboratory. Results: By acquiring the highest-statistics Cl32 β-delayed γ-ray spectrum to date and exploiting a new sensitivity to γ-γ coincidences, this experiment has enabled the observation of nine previously unobserved β-delayed γ-ray transitions, leading to the inference of five β-decay transitions never before observed in Cl32 β-delayed γ decay. The set of observed states includes negative-parity states for the first time. By combining the new information with data from previous work, the lifetimes and partial widths of the 8861- and 9650-keV states of S32 have been determined. In addition, the P31(p,α)Si28 resonance strength of the 9650-keV state has been limited to ωγ<9.8 meV, which is an improvement over direct measurements. Conclusion: An enhanced decay scheme has been constructed. Most of the excited bound S32 states that would correspond to allowed and first-forbidden β-decay transitions have been observed, demonstrating the potential of β-decay experiments to approach complete spectroscopy measurements at the next generation of radioactive beam facilities. The observed positive-parity levels are well matched by sd shell-model calculations.