2,600 research outputs found
The Proton Electric Pygmy Dipole Resonance
The evolution of the low-lying E1 strength in proton-rich nuclei is analyzed
in the framework of the self-consistent relativistic Hartree-Bogoliubov (RHB)
model and the relativistic quasiparticle random-phase approximation (RQRPA).
Model calculations are performed for a series of N=20 isotones and Z=18
isotopes. For nuclei close to the proton drip-line, the occurrence of
pronounced dipole peaks is predicted in the low-energy region below 10 MeV
excitation energy. From the analysis of the proton and neutron transition
densities and the structure of the RQRPA amplitudes, it is shown that these
states correspond to the proton pygmy dipole resonance.Comment: 7 pages, 4 figures, to be published in Phys. Rev. Let
Relativistic mean-field description of the dynamics of giant resonances
The relativistic mean-field theory provides a framework in which the nuclear
many-body problem is described as a self-consistent system of nucleons and
mesons. In the mean-field approximation, the self-consistent time evolution of
the nuclear system describes the dynamics of collective motion: nuclear
compressibility from monopole resonances, regular and chaotic dynamics of
isoscalar and isovector collective vibrations.Comment: LaTeX, 10 pages, 5 figures, Invited Talk, Topical Conference on Giant
resonances, Varenna, May 1998, to be published in Nucl. Phys.
Relativistic description of exotic collective excitation phenomena in atomic nuclei
The low-lying dipole and quadrupole states in neutron rich nuclei, are
studied within the fully self-consistent relativistic quasiparticle
random-phase approximation (RQRPA), formulated in the canonical basis of the
Relativistic Hartree-Bogoliubov model (RHB), which is extended to include the
density dependent interactions. In heavier nuclei, the low-lying E1 excited
state is identified as a pygmy dipole resonance (PDR), i.e. as a collective
mode of excess neutrons oscillating against a proton-neutron core. Isotopic
dependence of the PDR is characterized by a crossing between the PDR and
one-neutron separation energies. Already at moderate proton-neutron asymmetry
the PDR peak is calculated above the neutron emission threshold, indicating
important implications for the observation of the PDR in (gamma,gamma')
scattering, and on the theoretical predictions of the radiative neutron capture
rates in neutron-rich nuclei. In addition, a novel method is suggested for
determining the neutron skin of nuclei, based on measurement of excitation
energies of the Gamow-Teller resonance relative to the isobaric analog state.Comment: 8 pages, 3 figures, invited talk at the international workshop
"Blueprints for the nucleus: From First Principles to Collective Motion", May
17-22. 2004, Istanbul, Turkey; to appear in Int. J. Mod. Phys.
Toroidal dipole resonances in the relativistic random phase approximation
The isoscalar toroidal dipole strength distributions in spherical nuclei are
calculated in the framework of a fully consistent relativistic random phase
approximation. It is suggested that the recently observed "low-lying component
of the isoscalar dipole mode" might in fact correspond to the toroidal giant
dipole resonance. Although predicted by several theoretical models, the
existence of toroidal resonances has not yet been confirmed in experiment. The
strong mixing between the toroidal resonance and the dipole compression mode
might help to explain the large discrepancy between theory and experiment on
the position of isoscalar giant dipole resonances.Comment: 10 pages, 3 figures; Phys.Rev.C, in prin
Pygmy dipole resonances in relativistic random phase approximation
The isovector dipole response in Pb is described in the framework of
a fully self-consistent relativistic random phase approximation. The NL3
parameter set for the effective mean-field Lagrangian with nonlinear meson
self-interaction terms, used in the present calculations, reproduces ground
state properties as well as the excitation energies of giant resonances in
nuclei. In addition to the isovector dipole resonance in Pb, the
present analysis predicts the occurrence of low-lying E1 peaks in the energy
region between 7 and 11 MeV. In particular, a collective state has been
identified whose dynamics correspond to that of a dipole pygmy resonance: the
vibration of the excess neutrons against the inert core composed of equal
number of protons and neutrons.Comment: LaTex 7 pages, 4 eps Figs, submitted to Phys. Lett.
Microscopic calculation of 240Pu scission with a finite-range effective force
Hartree-Fock-Bogoliubov calculations of hot fission in
have been performed with a newly-implemented code that uses the D1S
finite-range effective interaction. The hot-scission line is identified in the
quadrupole-octupole-moment coordinate space. Fission-fragment shapes are
extracted from the calculations. A benchmark calculation for
is obtained and compared to results in the literature. In
addition, technical aspects of the use of HFB calculations for fission studies
are examined in detail. In particular, the identification of scission
configurations, the sensitivity of near-scission calculations to the choice of
collective coordinates in the HFB iterations, and the formalism for the
adjustment of collective-variable constraints are discussed. The power of the
constraint-adjustment algorithm is illustrated with calculations near the
critical scission configurations with up to seven simultaneous constraints.Comment: 18 pages, 24 figures, to be published in Physical Review
Inclusive charged-current neutrino-nucleus reactions calculated with the relativistic quasiparticle random phase approximation
Inclusive neutrino-nucleus cross sections are calculated using a consistent
relativistic mean-field theoretical framework. The weak lepton-hadron
interaction is expressed in the standard current-current form, the nuclear
ground state is described with the relativistic Hartree-Bogoliubov model, and
the relevant transitions to excited nuclear states are calculated in the
relativistic quasiparticle random phase approximation. Illustrative test
calculations are performed for charged-current neutrino reactions on C,
O, Fe, and Pb, and results compared with previous studies
and available data. Using the experimental neutrino fluxes, the averaged cross
sections are evaluated for nuclei of interest for neutrino detectors. We
analyze the total neutrino-nucleus cross sections, and the evolution of the
contribution of the different multipole excitations as a function of neutrino
energy. The cross sections for reactions of supernova neutrinos on O and
Pb target nuclei are analyzed as functions of the temperature and
chemical potential.Comment: 28 pages, 8 figures, 2 tables, submitted to Phys. Rev.
Nonlinear dynamics of giant resonances in atomic nuclei
The dynamics of monopole giant resonances in nuclei is analyzed in the
time-dependent relativistic mean-field model. The phase spaces of isoscalar and
isovector collective oscillations are reconstructed from the time-series of
dynamical variables that characterize the proton and neutron density
distributions. The analysis of the resulting recurrence plots and correlation
dimensions indicate regular motion for the isoscalar mode, and chaotic dynamics
for the isovector oscillations. Information-theoretic functionals identify and
quantify the nonlinear dynamics of giant resonances in quantum systems that
have spatial as well as temporal structure.Comment: 24 pages, RevTeX, 15 PS figures, submitted Phys. Rev.
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