Proton single-particle states in the neutron-rich 23F nucleus

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. By comparison of the population strengths for excited states in these reactions, we deduced the character of the excited states. The levels and γ-decay scheme in 23F were proposed based on de-excitation γ-rays and the products of these reactions. We found that the 2268- and 4059-keV levels have strong proton single-particle nature of the s1/2 and d3/2 orbitals, respectively, by analysis of the population strengths and the angular distributions of the states. These single-particle states are located at higher excitation energies than the shell model predictions for the USD and SDPF-M interactions, which indicates that the centroid energy gaps for πd5/2-πs1/2 and πd5/2-πd3/2 are wider than predicted.