Neutron occupancy of the 0 d 5 / 2 orbital and the N = 16 shell closure in 24O

摘要

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