Neutron-unbound excited states of N23

Abstract

Neutron unbound states in23 N were populated via proton knockout from an 83.4 MeV/nucleon 24 O beam on a liquid deuterium target. The two-body decay energy displays two peaks at E1 ∼ 100 keV and E2 ∼ 1 MeV with respect to the neutron separation energy. The data are consistent with shell model calculations predicting resonances at excitation energies of ∼ 3.6 MeV and ∼ 4.5 MeV. The selectivity of the reaction implies that these states correspond to the first and second 3/2 − states. The energy of the first state is about 1.3 MeV lower than the first excited 2 + in 24 O. This decrease is largely due to coupling with the πp −1 3/2 hole along with a small reduction of the N = 16 shell gap in 23 N.