Complete Decay Spectroscopy of Chlorine Isotopes with the FRIB Decay Station Initiator

The main scientific goal of Radioactive ion Beam Facilities is to enable studies of exotic nuclei and thus quantify changes in nuclear structure in the short-lived nuclei with unusual numbers of protons and neutrons. Advanced detection systems are implemented to maximize detection efficiency and energy resolution to capitalize on the development of exotic isotope beams. The US Facility for Rare Isotope Beams (FRIB, East Lansing, Michigan) became operational in 2022. The first experiments at FRIB used the FRIB Decay Station Initiator (FDSi), a multi-detector system developed for measurements of exotic radioactive nuclei. FDSI combines advanced individual detectors from multiple institutions to comprehensively study decay observables. This work is based on results from one of the earliest FDSi experiments, which enabled a complete decay spectroscopic study of the β decay of chlorine isotopes with neutron number ≈ 28. These nuclei are in a transitional region between the spherical Calcium-48 and the deformed Silicon-42, known to be located in the second island of inversion. Complementary to the previous reaction measurements, the experimental studies of Chlorine decay provide a benchmark for theoretical models as one increases the neutron-to-proton ratio.