Proton Shell Structure in Neutron-rich 23F

The proton shell structure in neutron-rich fluorine 23F was investigated using the in-beam γ-ray spectroscopy technique via the proton transfer reaction onto the 22O nucleus. We also measured the α inelastic scattering on 23F, the neutron knockout from 24F, and the two-nucleon knockout from 25Ne using a cocktail secondary beam. The excited states were identified by de-excitation γ-rays coincident with outgoing 23F, and we found the proton single-particle states at 2268 and 4059 keV by comparison of the population strengths among these reactions. These states were respectively assigned to have ℓ=0 and ℓ=2 by the angular distributions obtained in the transfer reaction, and therefore they were considered to have the configurations of πs1/2 and πd3/2. The excitation energies of these states are located at higher excitation energies than the shell model predictions for the USD and SDPF-M interactions, which may indicate that the centroid energy gaps between πd5/2 and πs1/2 are wider than predictions.