Search for neutron decoupling in O22 via the (d,d'γ) reaction

We have searched for valence neutron decoupling in O22, a phenomenon recently observed in neutron-rich C, B, and lighter O nuclei. From the cross section of the (d,d'γ) reaction for the transition between the ground state and the first 2+ state of O22, 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 Mn/Mp compared to the N/Z value has been derived to be around 1. This result indicates that the O22 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.