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

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 (∼900MeV/u). The inclusive data have been interpreted within the eikonal approximation. The evolution of the single-particle occupancy in the ground state of 33^,34 ^,35Al has been studied and compared with shell model predictions. The inferred 2s_1/2 neutron occupancy in the 33Al 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 34Al, similarly to 33Mg. The single-particle 1f_7/2 occupancy shows a gradual increase at N=22. Correspondingly, a decrease of the 1d_3/2 strength has been observed.