We have searched for valence neutron decoupling in ${}^{22}\mathrm{O}$, a phenomenon recently observed in neutron-rich C, B, and lighter O nuclei. From the cross section of the ($d,d^{\text{'}}\gamma$) reaction for the transition between the ground state and the first $2^{+}$ state of ${}^{22}\mathrm{O}$, 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 ${}^{22}\mathrm{O}$ 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.

• Received 9 May 2006

DOI:https://doi.org/10.1103/PhysRevC.74.017306