One-neutron removal reactions on Al isotopes around the N = 20 shell closure

Abstract

The one-neutron removal cross sections of neutron-rich Al isotopes and longitudinal momentum distributions of the residues have been measured for A = 33 to 36 at relativistic energies ([approximate to] 900 MeV/u). The inclusive data have been interpreted within the eikonal approximation. The evolution of the single-particle occupancy in the ground state of [superscript 33,34,35]Al has been studied and compared with shell model predictions. The inferred 2s[subscript 1/2] neutron occupancy in the [superscript 33]Al ground-state wave function is 20% to 40% lower than the predicted one. The inclusive data do not exclude the presence of intruder states. Some intruder l = 1 occupancy is found in [superscript 34]Al, similarly to [superscript 33]Mg. The single-particle 1f[subscript 7/2] occupancy shows a gradual increase at N = 22. Correspondingly, a decrease of the 1d[subscript 3/2] strength has been observed.