$N=14$ Shell Closure in ${}^{22}\mathrm{O}$ Viewed through a Neutron Sensitive Probe

To investigate the behavior of the $N=14$ neutron gap far from stability with a neutron-sensitive probe, proton elastic and $2_1^{+}$ inelastic scattering angular distributions for the neutron-rich nucleus ${}^{22}\mathrm{O}$ were measured using the MUr à STrip detector array at the Grand Accélérateur National d’Ions Lourds facility. A deformation parameter ${\beta }_{p,p^{\prime }}=0.26\pm 0.04$ is obtained for the $2_1^{+}$ state, much lower than in ${}^{20}\mathrm{O}$, showing a weak neutron contribution to this state. A microscopic analysis was performed using matter and transition densities generated by continuum Skyrme-Hartree-Fock-Bogoliubov and quasiparticle random phase approximation calculations, respectively. The ratio of neutron to proton contributions to the $2_1^{+}$ state is found close to the $N/Z$ ratio, demonstrating a strong $N=14$ shell closure in the vicinity of the neutron drip line.

Figure 1

(a) Scatter plot of recoiling proton energy versus scattering angle in the laboratory frame for the ${}^{22}\mathrm{O}$ beam. (b) ${}^{22}\mathrm{O}$ excitation energy spectrum deduced from the proton kinematics.

Figure 2

Elastic and $2_1^{+}$ inelastic angular distributions of ${}^{22}\mathrm{O}$ at $46.6\mathrm{A}\mathrm{MeV}$ (dots). DWBA using the phenomenological KD global optical potential (solid lines) and folding model (dashed lines) calculations are shown (see text).