Probing the neutron skin thickness in collective modes of excitation

Physics Department, Faculty of Science, University of Zagreb, Croatia

^a e-mail: npaar@phy.hr

Published online: 20 March 2014

Abstract

Nuclear collective motion provides valuable constraint on the size of neutron-skin thickness and the properties of nuclear matter symmetry energy. By employing relativistic nuclear energy density functional (RNEDF) and covariance analysis related to χ² fitting of the model parameters, relevant observables are identified for dipole excitations, which strongly correlate with the neutron-skin thickness (r_np), symmetry energy at saturation density (J) and slope of the symmetry energy (L). Using the RNEDF framework and experimental data on pygmy dipole strength (⁶⁸Ni, ¹³²Sn, ²⁰⁸Pb) and dipole polarizability (²⁰⁸Pb), it is shown how the values of J, and L, and r_np are constrained. The isotopic dependence of moments associated to dipole excitations in ^116–136Sn shows that the low-energy dipole strength and polarizability in neutron-rich nuclei display strong sensitivity to the symmetry energy parameter J, more pronounced than in isotopes with moderate neutron-to-proton number ratios.