Collapse of the N=28 shell closure in S42i

Abstract

The energies of the excited states in very neutron-rich S42i and P41,43 have been measured using in-beam γ-ray spectroscopy from the fragmentation of secondary beams of S42,44 at 39AMeV. The low 2+ energy of S42i, 770(19) keV, together with the level schemes of P41,43, provides evidence for the disappearance of the Z=14 and N=28 spherical shell closures, which is ascribed mainly to the action of proton-neutron tensor forces. New shell model calculations indicate that S42i is best described as a well-deformed oblate rotor. © 2007 The American Physical Society.