Search

A concentration of dipole strength at energies below the giant dipole resonance was observed in neutron-rich nuclei around 132Sn in an experiment using the FRS-LAND setup. This so-called “pygmy” dipole strength can be related to the parameters of the symmetry energy and to the neutron skin thickness on the grounds of a relativistic quasiparticle random-phase approximation. Using this ansatz and the experimental findings for 130Sn and 132Sn, we derive a value of the symmetry energy pressure of p̄0 = 2.2±0.5 MeV/fm3. Neutron skin thicknesses of Rn-Rp = 0.23±0.03 fm and 0.24±0.03 fm for 130Sn and 132Sn, respectively, have been determined. Preliminary results on 68Ni from a similar experiment using an improved setup indicate an enhanced cross section at low energies, while the results for 58Ni are in accordance with results from photoabsorption measurements. [ABSTRACT FROM AUTHOR]

Multipole excitation phenomena in exotic nuclei are investigated within the framework of the fully self-consistent Relativistic Quasi-particle Random-Phase Approximation (RQRPA) based on the Relativistic Hartree-Bogoliubov (RHB) model with density dependent meson-nucleon couplings, and finite-range Gogny interaction to account for the pairing correlations. The RHB+RQRPA study of nuclei towards the proton drip-line indicates the appearance of an exotic collective excitation mode: the proton pygmy dipole resonance, due to oscillations of loosely bound protons against the rest of nucleons. The continuum RPA using Skyrme interactions is employed in a study of doubly magic 48Ni, resulting in a rather broad distribution of the low-lying dipole strength, due to the coupling to the continuum. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

The self-consistent relativistic proton-neutron quasiparticle random phase approximation (PN-RQRPA) has been employed in the analysis of charge-exchange modes: isobaric analog states (IAS) and Gamow-Teller resonances (GTR). A particularly interesting application is the study of the relation between the neutron skin of nuclei and the difference of excitation energies of the GTR and IAS. In addition to important information on basic nuclear structure, effective isovector interactions, and neutron-rich matter for astrophysical applications, the determination of neutron density distributions is crucial for the analysis of atomic parity-violating experiments. Detailed PN-RQRPA calculations of nuclear properties of a sequence of Sn isotopes, have shown that the isotopic dependence of the energy spacings between the GTR and IAS provides a measure of the evolution of the difference between the radii of the neutron and proton density distributions. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]