Inverse-kinematics proton scattering from S 42 , 44 ,   P 41 , 43 , and the collapse of the N = 28 major shell closure

Excited states of the neutron-rich isotopes S 42,44 and P 41,43 have been investigated via inverse-kinematics proton scattering from a liquid hydrogen target, using the GRETINA γ -ray tracking array to extract inelastic-scattering cross sections. Deformation lengths of the 21+ excitations in S 42,44 have been observed and, when combined with deformation lengths determined with electromagnetic probes, yield the ratio of neutron-to-proton matrix elements Mn/Mp for the 21+ excitations in these nuclei. The present results for P 41,43(p,p') are used to compare two shell-model interactions, SDPF-U and SDPF-MU. As in a recent study of Si42 , the present results on P 41,43 favor the SDPF-MU interaction.