Excitation of Isovector Spin-Dipole Resonances and Neutron Skin of Nuclei

Abstract

The cross sections of the isovector spin-dipole resonances (SDR) in the Sb isotopes excited by the ${(}^{3}\mathrm{He},t)$ charge-exchange reaction at 450 MeV for $0\ifmmode^\circ\else\textdegree\fi{}\ensuremath{\le}{\ensuremath{\theta}}_{t}\ensuremath{\le}1.15\ifmmode^\circ\else\textdegree\fi{}$ have been measured. The results are compared with the predicted sum-rule strengths related to the difference of neutron and proton root-mean-square radii. Within the model used, the radii differences (neutron-skin thicknesses) deduced for ${}^{114}\mathrm{Sn}$, ${}^{116}\mathrm{Sn}$, ${}^{118}\mathrm{Sn}$, ${}^{122}\mathrm{Sn}$, and ${}^{124}\mathrm{Sn}$ are $\ensuremath{\le}0.09$, $0.12\ifmmode\pm\else\textpm\fi{}0.06$, $0.13\ifmmode\pm\else\textpm\fi{}0.06$, $0.22\ifmmode\pm\else\textpm\fi{}0.07$, and $0.19\ifmmode\pm\else\textpm\fi{}0.07\mathrm{fm}$, respectively. This result suggests a new method for the measurement of the neutron-skin thicknesses of unstable nuclei.