Isovector deformation and its link to the neutron shell closure

Abstract

DWBA analysis of the inelastic ${}^{30-40}$S$(p,p^{\prime })$ and ${}^{18-22}$O$(p,p^{\prime })$ scattering data measured in the inverse kinematics has been performed to determine the isoscalar (${\delta }_0$) and isovector (${\delta }_1$) deformation lengths of the 2${}_1^{+}$ excitations in the Sulfur and Oxygen isotopes using a compact folding approach. A systematic $N$-dependence of ${\delta }_0$ and ${\delta }_1$ has been established which shows a link between ${\delta }_1$ and the neutron-shell closure. Strong isovector deformations were found in several cases, e.g., the 2${}_1^{+}$ state in ${}^{20}$O where ${\delta }_1$ is nearly three times larger than ${\delta }_0$. These results confirm the relation ${\delta }_1>{\delta }_0$ anticipated from the core polarization by the valence neutrons in the open-shell (neutron rich) nuclei. The effect of neutron shell closure at N=14 or 16 has been discussed based on the folding model analysis of the inelastic ${}^{22}$O+$p$ scattering data at 46.6 MeV/u measured recently at GANIL.

Comments: Talk given at RNB7 conference (Cortina d'Ampezzo, Italy, July 3-7, 2006); 4 pages, 4 figures, to appear in Eur. Phys. Journal A