Expansion of the 16O-core in neutron drip-line nuclei: 23O and 24O

We study an effect of the expansion of the core nucleus to the radius of 23O and 24O. In order to clarify the importance of the expansion of the core, we perform two calculations; an m-scheme approach of the cluster-orbital shell model for systems and a simplified model approach for core+n and core+2n systems. We calculate the energy and r.m.s. radius of oxygen isotopes by using these two approaches and discuss the effect of the expansion of the 16O-core and the relation to the presence of valence neutrons. Furthermore, we propose a new approach of a coupled-channel model including a particle–hole excitation in the 16O-core and the motion of the valence neutron.