8 research outputs found
Microscopic description of nuclear vibrations: Relativistic QRPA and its extensions with quasiparticle-vibration coupling
The recent extensions of the covariant energy density functional theory with
the quasiparticle-vibration coupling (QVC) are reviewed. Formulation of the
Quasiparticle Random Phase Approximation (QRPA) in the relativistic framework
is discussed. Self-consistent extensions of the relativistic QRPA imply the QVC
which is implemented in two-body propagators in the nuclear medium. This
provides fragmentation of the QRPA states describing the damping of the
vibrational motion.Comment: Published in "50 Years of Nuclear BCS", edited by R. A. Broglia and
V.G. Zelevinsky, World Scientific (2013
Mode-coupling and the pygmy dipole resonance in a relativistic two-phonon model
A two-phonon version of the relativistic quasiparticle time blocking
approximation (RQTBA-2) represents a new class of many-body models for nuclear
structure calculations based on the covariant energy density functional. As a
fully consistent extension of the relativistic quasiparticle random phase
approximation (RQRPA), the two-phonon RQTBA implies a fragmentation of nuclear
states over two-quasiparticle and two-phonon configurations. This leads, in
particular, to a splitting-out of the lowest 1 state as a member of the
two-phonon quintuplet from the RQRPA pygmy dipole mode, thus
establishing a physical mixing between these three modes. The inclusion of the
two-phonon configurations in the model space allows to describe the positions
and the reduced transition probabilities of the lowest 1 states in isotopes
Sn as well as the low-energy fraction of the dipole strength
without any adjustment procedures. The model is also applied to the low-lying
dipole strength in neutron-rich Ni isotopes. Recent experimental
data for Ni are reproduced fairly well
Microscopic calculations of the characteristics of radiative nuclear reactions for double-magic nuclei
The neutron capture cross sections and average radiative widths Γγ of neutron resonances for two double-magic nuclei 132Sn and 208Pb have been calculated using the microscopic photon strength functions (PSF), which were obtained within the microscopic self-consistent version of the extended theory of finite Fermi systems in the time blocking approximation. For the first time, the microscopic PSFs have been obtained within the fully self-consistent approach with exact accounting for the single particle continuum (for 208Pb). The approach includes phonon coupling effects in addition to the standard RPA approach. The known Skyrme force has been used. The calculations of nuclear reaction characteristics have been performed with the EMPIRE 3.1 nuclear reaction code. Here, three nuclear level density (NLD) models have been used: the so-called phenomenological GSM, the EMPIRE specific (or Enhanced GSM) and the microscopical combinatorial HFB NLD models. For both considered characteristics we found a significant disagreement between the results obtained with the GSM and HFB NLD models. For 208Pb, a reasonable agreement has been found with systematic for the Γγ values with HFB NLD and with the experimental data for the HFB NLD average resonance spacing D0, while for these two quantities the differences between the values obtained with GSM and HFB NLD are of several orders of magnitude. The discrepancies between the results with the phenomenological EGLO PSF and microscopic RPA or TBA are much less for the same NLD model
Generalized Skyrme random-phase approximation for nucler resonances: Different trends for electric and magnetic modes
We discuss major differences between electric and magnetic excitations in nuclei appearing in self-consistent calculations based on Skyrme energy-density functionals (EDFs). For this we calculate collective low- and high-lying electric and magnetic excitations in 208Pb within a self-consistent Skyrme EDF approach using the random-phase approximation (RPA) and a more sophisticated particle-hole plus phonon-coupling model, coined the time-blocking approximation (TBA). Tools of analysis are Landau-Migdal parameters for bulk properties and the RPA and TBA results for finite nuclei. We show that the interplay between the effective mass and the effective particle-hole interaction, well known in the Landau-Migdal theory, renders the final results rather independent of the effective mass by virtue of the “backflow effect.” It explains the success of self-consistent calculations of electric transitions in such approaches. This effect, however, is absent in the magnetic case and leads to higher fluctuations in the results. It calls for further developments of the Skyrme functional in the spin channel
Konzepte zur dezentralen Raumentwicklung in der Tuerkei
TIB: RN 5854 (35) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman