Probing Deformation Around Z=14 and N=28: Decay Spectroscopy of Exotic Si Isotopes

The N=28 shell closure, traditionally robust in stable nuclei like ⁴⁸Ca, is observed to erode far from stability mainly due to spin-flip interactions, the tensor force, and/or three-body effects. These influences reduce the νf_7/2-νp_3/2 gap promoting deformation in neutron-rich isotones below Z=20. ⁴²Si with N= 28 is presumed to have an oblate ground state in spite of the 28 neutrons that form it. In this work, we report on decay spectroscopy of exotic Si isotopes, produced and studied at the Facility for Rare Isotope Beams (FRIB) using the FRIB Decay Station initiator (FDSi). The decay spectroscopy of ^41,42Si attempted for the first time will be reported. The observed level-scheme, intensities of low-lying states populated via β, βn, and potentially β2n decay to P isotopes will project a detailed picture of this region of the chart of nuclides. Together with measured half-lives of the parent isotopes, we will be able illuminate the structure of isotopes near N=28. The results will provide benchmarks for state-of-the-art shell-model calculations and help clarify shape evolution along the N=28 isotones.