Isovector dipole strength in nuclei with extreme neutron excess

Abstract

The $E1$ strength is systematically analyzed in very neutron-rich Sn nuclei, beyond $^{132}\mathrm{Sn}$ until $^{166}\mathrm{Sn}$, within the relativistic quasiparticle random phase approximation. The great neutron excess favors the appearance of a deformed ground state for $^{142\ensuremath{-}162}\mathrm{Sn}$. 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 spherical nuclei like $^{132}\mathrm{Sn}$ for the experimental study of low-lying $E1$ strength.