How Different is the Core of 25F from 24Og.s. ?

The structure of a neutron-rich F-25 nucleus is investigated by a quasifree (p, 2p) knockout reaction at 270A MeV in inverse kinematics. The sum of spectroscopic factors of pi 0d(5/2) orbital is found to be 1.0 +/- 0.3. However, the spectroscopic factor with residual O-24 nucleus being in the ground state is found to be only 0.36 +/- 0.13, while those in the excited state is 0.65 +/- 0.25. The result shows that the O-24 core of F-25 nucleus significantly differs from a free O-24 nucleus, and the core consists of similar to 35% O-24(g.s.). and similar to 65% excited O-24. The result may infer that the addition of the 0d(5/2) proton considerably changes neutron structure in F-25 from that in O-24, which could be a possible mechanism responsible for the oxygen dripline anomaly.