The isovector dipole strength in nuclei with extreme neutron excess

Abstract

The E1 strength is systematically analyzed in very neutron-rich Sn nuclei, beyond ${}^{132}$Sn until ${}^{166}$Sn, within the Relativistic Quasiparticle Random Phase Approximation. The great neutron excess favors the appearance of a deformed ground state for ${}^{142-162}$Sn. The evolution of the low-lying strength in deformed nuclei is determined by the interplay of two factors, isospin asymmetry and deformation: while greater neutron excess increases the total low-lying strength, deformation hinders and spreads it. Very neutron rich deformed nuclei may not be as good candidates as stable spherical nuclei like ${}^{132}$Sn for the experimental study of low-lying E1 strength.