Extended p3/2 Neutron Orbital and the N=32 Shell Closure in 52Ca

The one-neutron knockout from 52Ca in inverse kinematics onto a proton target was performed at similar to 230 MeV/nucleon combined with prompt 7 spectroscopy. Exclusive quasifree scattering cross sections to bound states in 51Ca and the momentum distributions corresponding to the removal of 1f7=2 and 2p3=2 neutrons were measured. The cross sections, interpreted within the distorted-wave impulse approximation reaction framework, are consistent with a shell closure at the neutron number N = 32, found as strong as at N = 28 and N = 34 in Ca isotopes from the same observables. The analysis of the momentum distributions leads to a difference of the root-mean-square radii of the neutron 1f7=2 and 2p3=2 orbitals of 0.61(23) fm, in agreement with the modified-shell-model prediction of 0.7 fm suggesting that the large root-mean-square radius of the 2p3=2 orbital in neutron-rich Ca isotopes is responsible for the unexpected linear increase of the charge radius with the neutron number.

Automated summary

In this study, one-neutron knockout from 52Ca onto a proton target in inverse kinematics was performed. Prompt 7 spectroscopy was combined with the experiment at an energy of about 230 MeV/nucleon. The exclusive quasifree scattering cross sections to bound states in 51Ca and the momentum distributions corresponding to the removal of 1f7=2 and 2p3=2 neutrons were measured. The results indicate a shell closure at the neutron number N = 32 in Ca isotopes, similar to the shell closures at N = 28 and N = 34. Analysis of the momentum distributions reveals that the larger root-mean-square radius of the 2p3=2 orbital in neutron-rich Ca isotopes is responsible for the unexpected linear increase of the charge radius with the neutron number.