Neutron-unbound excited states of N 23

Neutron unbound states in N23 were populated via proton knockout from an 83.4 MeV/nucleon O24 beam on a liquid deuterium target. The two-body decay energy displays two peaks at E1∼100keV and E2∼1MeV with respect to the neutron separation energy. The data are consistent with shell model calculations predicting resonances at excitation energies of ∼3.6MeV and ∼4.5MeV. 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 O24. This decrease is largely due to coupling with the πp3/2-1 hole along with a small reduction of the N=16 shell gap in N23.