Neutron transition strengths of $2_1^{+}$ states in the neutron rich Oxygen isotopes determined from inelastic proton scattering

Abstract

A coupled-channel analysis of the ${}^{18,20,22}$O$(p,p^{\prime })$ data has been performed to determine the neutron transition strengths of 2${}_1^{+}$ states in Oxygen targets, using the microscopic optical potential and inelastic form factor calculated in the folding model. A complex density- and \emph{isospin} dependent version of the CDM3Y6 interaction was constructed, based on the Brueckner-Hatree-Fock calculation of nuclear matter, for the folding model input. Given an accurate isovector density dependence of the CDM3Y6 interaction, the isoscalar (${\delta }_0$) and isovector (${\delta }_1$) deformation lengths of 2${}_1^{+}$ states in ${}^{18,20,22}$O have been extracted from the folding model analysis of the $(p,p^{\prime })$ data. A specific $N$-dependence of ${\delta }_0$ and ${\delta }_1$ has been established which can be linked to the neutron shell closure occurring at $N$ approaching 16. The strongest isovector deformation was found for 2${}_1^{+}$ state in ${}^{20}$O, with ${\delta }_1$ about 2.5 times larger than ${\delta }_0$, which indicates a strong core polarization by the valence neutrons in ${}^{20}$O. The ratios of the neutron/proton transition matrix elements ($M_n/M_p$) determined for 2${}_1^{+}$ states in ${}^{18,20}$O have been compared to those deduced from the mirror symmetry, using the measured $B(E2)$ values of 2${}_1^{+}$ states in the proton rich ${}^{18}$Ne and ${}^{20}$Mg nuclei, to discuss the isospin impurity in the $2_1^{+}$ excitation of the $A=18,T=1$ and $A=20,T=2$ isobars.

Version accepted for publication in Physical Review C

References in corpus (3)

• Nuclear rainbow scattering and nucleus-nucleus potential
• Folding model study of the isobaric analog excitation: isovector density dependence, Lane potential and nuclear symmetry energy
• Isovector deformation and its link to the neutron shell closure