2,633 research outputs found
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
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
Exotic modes of excitation in atomic nuclei far from stability
We review recent studies of the evolution of collective excitations in atomic
nuclei far from the valley of -stability. Collective degrees of freedom
govern essential aspects of nuclear structure, and for several decades the
study of collective modes such as rotations and vibrations has played a vital
role in our understanding of complex properties of nuclei. The multipole
response of unstable nuclei and the possible occurrence of new exotic modes of
excitation in weakly-bound nuclear systems, present a rapidly growing field of
research, but only few experimental studies of these phenomena have been
reported so far. Valuable data on the evolution of the low-energy dipole
response in unstable neutron-rich nuclei have been gathered in recent
experiments, but the available information is not sufficient to determine the
nature of observed excitations. Even in stable nuclei various modes of giant
collective oscillations had been predicted by theory years before they were
observed, and for that reason it is very important to perform detailed
theoretical studies of the evolution of collective modes of excitation in
nuclei far from stability. We therefore discuss the modern theoretical tools
that have been developed in recent years for the description of collective
excitations in weakly-bound nuclei. The review focuses on the applications of
these models to studies of the evolution of low-energy dipole modes from stable
nuclei to systems near the particle emission threshold, to analyses of various
isoscalar modes, those for which data are already available, as well as those
that could be observed in future experiments, to a description of
charge-exchange modes and their evolution in neutron-rich nuclei, and to
studies of the role of exotic low-energy modes in astrophysical processes.Comment: 123 pages, 59 figures, submitted to Reports on Progress in Physic
Structure of the doublet bands in doubly odd nuclei: The case of
The structure of the doublet bands in is
investigated within the framework of the Interacting Vector Boson Fermion Model
(IVBFM). A new, purely collective interpretation of these bands is given on the
basis of the used boson-fermion dynamical symmetry of the model. The energy
levels of the doublet bands as well as the absolute and
transition probabilities between the states of both yrast and yrare bands are
described quite well. The observed odd-even staggering of both and
values is reproduced by the introduction of an appropriate interaction
term of quadrupole type, which produces such a staggering effect in the
transition strengths. The calculations show that the appearance of doublet
bands in certain odd-odd nuclei could be a consequence of the realization of a
larger dynamical symmetry based on the non-compact supersymmetry group
.Comment: 12 pages, 8 figure
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.
Neutron star structure and collective excitations of finite nuclei
We study relationships between properties of collective excitations in finite
nuclei and the phase transition density and pressure at the inner
edge separating the liquid core and the solid crust of a neutron star. A
theoretical framework that includes the thermodynamic method, relativistic
nuclear energy density functionals and the quasiparticle random-phase
approximation is employed in a self-consistent calculation of and
collective excitations in nuclei. The covariance analysis shows that properties
of charge-exchange dipole transitions, isovector giant dipole and quadrupole
resonances and pygmy dipole transitions are correlated with the core-crust
transition density and pressure. A set of relativistic nuclear energy density
functionals, characterized by systematic variation of the density dependence of
the symmetry energy of nuclear matter, is used to constrain possible values for
. By comparing the calculated excitation energies of giant
resonances, energy weighted pygmy dipole strength, and dipole polarizability
with available data, we obtain the weighted average values: fm and MeV fm.Comment: 4 pages, 3 figures, paper submitted for publicatio
Information content of the weak-charge form factor
Parity-violating electron scattering provides a model-independent
determination of the nuclear weak-charge form factor that has widespread
implications across such diverse areas as fundamental symmetries, nuclear
structure, heavy-ion collisions, and neutron-star structure. We assess the
impact of precise measurements of the weak-charge form factor of Ca
and Pb on a variety of nuclear observables, such as the neutron skin
and the electric-dipole polarizability. We use the nuclear Density Functional
Theory with several accurately calibrated non-relativistic and relativistic
energy density functionals. To assess the degree of correlation between nuclear
observables and to explore systematic and statistical uncertainties on
theoretical predictions, we employ the chi-square statistical covariance
technique. We find a strong correlation between the weak-charge form factor and
the neutron radius, that allows for an accurate determination of the neutron
skin of neutron-rich nuclei. We determine the optimal range of the momentum
transfer that maximizes the information content of the measured weak-charge
form factor and quantify the uncertainties associated with the strange quark
contribution. Moreover, we confirm the role of the electric-dipole
polarizability as a strong isovector indicator. Accurate measurements of the
weak-charge form factor of Ca and Pb will have a profound
impact on many aspects of nuclear theory and hadronic measurements of neutron
skins of exotic nuclei at radioactive-beam facilities.Comment: 10 pages, 4 figure
Collective excitations in the Unitary Correlation Operator Method and relativistic QRPA studies of exotic nuclei
The collective excitation phenomena in atomic nuclei are studied in two
different formulations of the Random Phase Approximation (RPA): (i) RPA based
on correlated realistic nucleon-nucleon interactions constructed within the
Unitary Correlation Operator Method (UCOM), and (ii) relativistic RPA (RRPA)
derived from effective Lagrangians with density-dependent meson-exchange
interactions. The former includes the dominant interaction-induced short-range
central and tensor correlations by means of an unitary transformation. It is
shown that UCOM-RPA correlations induced by collective nuclear vibrations
recover a part of the residual long-range correlations that are not explicitly
included in the UCOM Hartree-Fock ground state. Both RPA models are employed in
studies of the isoscalar monopole resonance (ISGMR) in closed-shell nuclei
across the nuclide chart, with an emphasis on the sensitivity of its properties
on the constraints for the range of the UCOM correlation functions. Within the
Relativistic Quasiparticle RPA (RQRPA) based on Relativistic Hartree-Bogoliubov
model, the occurrence of pronounced low-lying dipole excitations is predicted
in nuclei towards the proton drip-line. From the analysis of the transition
densities and the structure of the RQRPA amplitudes, it is shown that these
states correspond to the proton pygmy dipole resonance.Comment: 15 pages, 4 figures, submitted to Physics of Atomic Nuclei,
conference proceedings, "Frontiers in the Physics of Nucleus", St.
Petersburg, 28. June-1. July, 200
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