The first experiment at FRIB Decay Station initiator (FDSi)

Atomic nuclei are quantum many-body systems consisting of two types of fermions -- proton and neutron. The exact solution to such systems is generally impossible. One of the most successful models to date, the nuclear shell model, simplifies the problem by assuming each proton or neutron moves independently in a mean field produced by all the other nucleons inside the nucleus. The resulting nuclear shell structure and magic numbers, such as Z or N=2, 8, 20, 28, 50, and 82, succeeded in interpreting the nuclear data taken near the stability line. In the last three decades, however, the advent of radioactive ion beams allowed the production and investigation of short-lived isotopes with extreme proton-neutron ratios. Unexpected properties have been observed in those nuclei compared to their stable counterparts, including the alterations of the shell structure and magic numbers. It has become a continuing effort in both experiments and theories to understand nuclear structure under extreme conditions.



The Facility for Rare Isotope Beams (FRIB) is the next-generation radioactive ion-beam facility that recently began operations at Michigan State University. It aims to offer world-unique and unprecedented access to exotic nuclei far from the stability line. Its first experiment was carried out at FRIB Decay Station initiator (FDSi) in May 2022, studying the decay properties of neutron-rich nuclei in the vicinity of ⁴²Si (Z=14, N=28). Nuclei in this region have long been of great interest because of the breakdown of the N=28 shell gap. In this contribution, I will give a general review of the experiment, including the experimental setup at FDSi, the first results that have been published recently [1], and ongoing analysis.



[1] H. L. Crawford et al., accepted by Phys. Rev. Lett.