Search for Neutron Decoupling in O-22 Via the (D,D ' Gamma) Reaction

We have searched for valence neutron decoupling in O-22, a phenomenon recently observed in neutron-rich C, B, and lighter O nuclei. From the cross section of the (d,d(')gamma) reaction for the transition between the ground state and the first 2(+) state of O-22, the neutron and proton deformation parameters have been deduced by distorted wave analysis using and reanalyzing the data of a previous Coulomb excitation measurement. The ratio of the neutron and proton multipole transition matrix elements M-n/M-p compared to the N/Z value has been derived to be around 1. This result indicates that the O-22 isotope has small and similar neutron and proton deformations, which is consistent with N=14 shell closure. Thus, the concept of neutron decoupling does not hold for this nucleus.