2,300 research outputs found
Comment on "Pygmy dipole response of proton-rich argon nuclei in random-phase approximation and no-core shell model"
In a recent article by C. Barbieri, E. Caurier, K. Langanke, and G.
Mart\'inez-Pinedo \cite{Bar.08}, low-energy dipole excitations were studied in
proton-rich Ar with random-phase approximation (RPA) and no-core
shell model (NCSM) using correlated realistic nucleon-nucleon interactions
obtained by the unitary correlation operator method (UCOM) \cite{Fel.98}. The
main objective of this Comment is to argue that the article \cite{Bar.08}
contains an inconsistency with respect to previous study of excitations in the
same UCOM-RPA framework using identical correlated Argonne V18 interaction
\cite{Paa.06}, it does not provide any evidence that the low-lying state
declared as pygmy dipole resonance in Ar indeed has the resonance-like
structure, and that prior to studying exotic modes of excitation away from the
valley of stability one should ensure that the model provides reliable
description of available experimental data on nuclear ground state properties
and excitations in nuclei. Although the authors aimed at testing the UCOM based
theory at the proton drip line, available experimental data that are used as
standard initial tests of theory frameworks at the proton drip line have not
been considered in the UCOM case (e.g., binding energies, one-proton separation
energies, two-proton separation energies).Comment: 2 pages, revised version, accepted for publication in Phys. Rev.
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
Optimizing the relativistic energy density functional with nuclear ground state and collective excitation properties
We introduce a new relativistic energy density functional constrained by the
ground state properties of atomic nuclei along with the isoscalar giant
monopole resonance energy and dipole polarizability in Pb. A unified
framework of the relativistic Hartree-Bogoliubov model and random phase
approximation based on the relativistic density-dependent point coupling
interaction is established in order to determine the DD-PCX parameterization by
minimization. This procedure is supplemented with the co-variance
analysis in order to estimate statistical uncertainties in the model parameters
and observables. The effective interaction DD-PCX accurately describes the
nuclear ground state properties including the neutron-skin thickness, as well
as the isoscalar giant monopole resonance excitation energies and dipole
polarizabilities. The implementation of the experimental data on nuclear
excitations allows constraining the symmetry energy close to the saturation
density, and the incompressibility of nuclear matter by using genuine
observables on finite nuclei in the minimization protocol, rather than
using pseudo-observables on the nuclear matter, or by relying on the ground
state properties only, as it has been customary in the previous studies.Comment: 6 pages, 3 figures, submitted to Physical Review
The nuclear symmetry energy and other isovector observables from the point of view of nuclear structure
In this contribution, we review some works related with the extraction of the
symmetry energy parameters from isovector nuclear excitations, like the giant
resonances. Then, we move to the general issue of how to assess whether
correlations between a parameter of the nuclear equation of state and a nuclear
observable are robust or not. To this aim, we introduce the covariance analysis
and we discuss some counter-intuitive, yet enlightening, results from it.Comment: To be published in the proceedings of the 2014 Zakopane Conference on
Nuclear Physics (Acta Physica Polonica B
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.
Calculation of stellar electron-capture cross sections on nuclei based on microscopic Skyrme functionals
A fully self-consistent microscopic framework for evaluation of nuclear
weak-interaction rates at finite temperature is introduced, based on Skyrme
functionals. The single-nucleon basis and the corresponding thermal occupation
factors of the initial nuclear state are determined in the finite-temperature
Skyrme Hartree-Fock model, and charge-exchange transitions to excited states
are computed using the finite-temperature RPA. Effective interactions are
implemented self-consistently: both the finite-temperature single-nucleon
Hartree-Fock equations and the matrix equations of RPA are based on the same
Skyrme energy density functional. Using a representative set of Skyrme
functionals, the model is applied in the calculation of stellar
electron-capture cross sections for selected nuclei in the iron mass group and
for neutron-rich Ge isotopes.Comment: 31 pages, 13 figures, submitted to Physical Review
Large-scale calculations of supernova neutrino-induced reactions in Z=8-82 target nuclei
Background: In the environment of high neutrino-fluxes provided in
core-collapse supernovae or neutron star mergers, neutrino-induced reactions
with nuclei contribute to the nucleosynthesis processes. A number of
terrestrial neutrino detectors are based on inelastic neutrino-nucleus
scattering and modeling of the respective cross sections allow predictions of
the expected detector reaction rates.
Purpose: To provide a self-consistent microscopic description of
neutrino-nucleus cross sections involving a large pool of Z = 8 - 82 nuclei for
the implementation in models of nucleosynthesis and neutrino detector
simulations.
Methods: Self-consistent theory framework based on relativistic nuclear
energy density functional is employed to determine the nuclear structure of the
initial state and relevant transitions to excited states induced by neutrinos.
The weak neutrino-nucleus interaction is employed in the current-current form
and a complete set of transition operators is taken into account.
Results: We perform large-scale calculations of charged-current
neutrino-nucleus cross sections, including those averaged over supernova
neutrino fluxes, for the set of even-even target nuclei from oxygen toward lead
(Z = 8 - 82), spanning N = 8 - 182 (OPb pool). The model calculations include
allowed and forbidden transitions up to J = 5 multipoles.
Conclusions: The present analysis shows that the self-consistent calculations
result in considerable differences in comparison to previously reported cross
sections, and for a large number of target nuclei the cross sections are
enhanced. Revision in modeling r-process nucleosynthesis based on a
self-consistent description of neutrino-induced reactions would allow an
updated insight into the origin of elements in the Universe and it would
provide the estimate of uncertainties in the calculated element abundance
patterns.Comment: 25 pages, 12 figures, submitted to Physical Review
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