In-beam γ -ray spectroscopy of S38–42

Abstract

The low-energy excitation level schemes of the neutron-rich $^{38--42}\mathrm{S}$ isotopes are investigated via in-beam $\ensuremath{\gamma}$-ray spectroscopy following the fragmentation of $^{48}\mathrm{Ca}$ and $^{46}\mathrm{Ar}$ projectiles on a $^{12}\mathrm{C}$ target at intermediate beam energies. Information on $\ensuremath{\gamma}\ensuremath{\gamma}$ coincidences complemented by comparisons to shell-model calculations were used to construct level schemes for these neutron-rich nuclei. The experimental data are discussed in the context of large-scale shell-model calculations with the SDPF-MU effective interaction in the $sd\text{\ensuremath{-}}pf$ shell. For the even-mass S isotopes, the evolution of the yrast sequence is explored as well as a peculiar change in decay pattern of the second ${2}^{+}$ states at $N=26$. For the odd-mass $^{41}\mathrm{S}$, a level scheme is presented that seems complete below 2.2 MeV and consistent with the predictions by the SDPF-MU shell-model Hamiltonian; this is a remarkable benchmark given the rapid shell and shape evolution at play in the S isotopes as the broken-down $N=28$ magic number is approached. Furthermore, the population of excited final states in projectile fragmentation is discussed.