Showing papers by "Nils Paar published in 2004"

Quasiparticle random phase approximation based on the relativistic Hartree-Bogoliubov model. II. Nuclear spin and isospin excitations

Abstract: The proton-neutron relativistic quasiparticle random-phase approximation (PN-RQRPA) is formulated in the canonical single-nucleon basis of the relativistic Hartree-Bogoliubov model, for an effective Lagrangian characterized by density-dependent meson-nucleon couplings. The model includes both the T = 1 and T = 0 pairing channels. Pair configurations formed from the fully or partially occupied states of positive energy in the Fermi sea, and the empty negative-energy states from the Dirac sea, are included in PN-RQRPA configuration space. The model is applied to the analysis of charge-exchange modes: isobaric analog resonances and Gamow-Teller resonances.

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.