Relativistic QRPA Description of Excitations in Exotic Nuclei

Abstract

The fully self-consistent relativistic quasiparticle random-phase approximation (RQRPA) has been formulated in the the canonical basis of the relativistic Hartree-Bogoliubov (RHB) model and applied in the analysis of the isovector dipole response in nuclei with large neutron excess. The dipole response is characterized by the fragmentation of the strength distribution and its spreading into the low-energy region and by mixing of isoscalar and isovector modes. In light nuclei the onset of dipole strength in the low-energy region is due to single particle excitations of the loosely bound neutrons. In heavier nuclei, low-lying dipole states appear, which are characterized by a more distributed structure of the RQRPA amplitude. An analysis of the transition densities and velocity distributions in neutron rich N=82 isotones and tin isotopes reveals the dynamics of the dipole pygmy resonance: the vibration of the excess neutrons against the inert core composed of equal numbers of protons and neutrons.