Neutron occupancy of the 0d5/2 orbital and the N=16 shell closure in 24O

Abstract

One-neutron knockout from 24O leading to the first excited state in 23O has been measured for a proton target at a beam energy of 62 MeV/nucleon. The decay energy spectrum of the neutron unbound state of 23O was reconstructed from the measured four momenta of the 22O fragment and emitted neutron. Asharp peak was found at Edecay=50 ±3keV, corresponding to an excited state in 23O at 2.78 ±0.11MeV, as observed in previous measurements. The longitudinal momentum distribution for this state was consistent with d-wave neutron knockout, providing support for a Jπassignment of 5/2+. The associated spectroscopic factor was deduced to be C2S(0d5/2) =4.1 ±0.4by comparing the measured cross section (σexp−1n=61 ±6mb) with a distorted wave impulse approximation calculation. Such a large occupancy for the neutron 0d5/2orbital is in line with the N=16shell closure in 24O.