438 research outputs found
Origin of the neutron skin thickness of 208Pb in nuclear mean-field models
We study whether the neutron skin thickness (NST) of 208Pb originates from
the bulk or from the surface of the nucleon density distributions, according to
the mean-field models of nuclear structure, and find that it depends on the
stiffness of the nuclear symmetry energy. The bulk contribution to NST arises
from an extended sharp radius of neutrons, whereas the surface contribution
arises from different widths of the neutron and proton surfaces. Nuclear models
where the symmetry energy is stiff, as typical relativistic models, predict a
bulk contribution in NST of 208Pb about twice as large as the surface
contribution. In contrast, models with a soft symmetry energy like common
nonrelativistic models predict that NST of 208Pb is divided similarly into bulk
and surface parts. Indeed, if the symmetry energy is supersoft, the surface
contribution becomes dominant. We note that the linear correlation of NST of
208Pb with the density derivative of the nuclear symmetry energy arises from
the bulk part of NST. We also note that most models predict a mixed-type
(between halo and skin) neutron distribution for 208Pb. Although the halo-type
limit is actually found in the models with a supersoft symmetry energy, the
skin-type limit is not supported by any mean-field model. Finally, we compute
parity-violating electron scattering in the conditions of the 208Pb parity
radius experiment (PREX) and obtain a pocket formula for the parity-violating
asymmetry in terms of the parameters that characterize the shape of the 208Pb
nucleon densities.Comment: 11 pages, 4 figures; minor stylistic changes in text, new Ref. [56]
added (new measurement of the neutron skin thickness of 208Pb
Analysis of bulk and surface contributions in the neutron skin of nuclei
The neutron skin thickness of nuclei is a sensitive probe of the nuclear
symmetry energy having multiple implications for nuclear and astrophysical
studies. However, precision measurements of this observable are difficult. The
analysis of the experimental data may imply some assumptions about the bulk or
surface nature of the formation of the neutron skin. Here, we study the bulk or
surface character of neutron skins of nuclei following from calculations with
Gogny, Skyrme, and covariant nuclear mean-field interactions. These
interactions are successful in describing nuclear charge radii and binding
energies but predict different values for neutron skins. We perform the study
by fitting two-parameter Fermi distributions to the calculated self-consistent
neutron and proton densities. We note that the equivalent sharp radius is a
more suitable reference quantity than the half-density radius parameter of the
Fermi distributions to discern between the bulk and surface contributions in
neutron skins. We present calculations for nuclei in the stability valley and
for the isotopic chains of Sn and Pb.Comment: 13 pages, 9 figure
Analysis of bulk and surface contributions in the neutron skin of nuclei
The neutron skin thickness of nuclei is a sensitive probe of the nuclear
symmetry energy having multiple implications for nuclear and astrophysical
studies. However, precision measurements of this observable are difficult. The
analysis of the experimental data may imply some assumptions about the bulk or
surface nature of the formation of the neutron skin. Here, we study the bulk or
surface character of neutron skins of nuclei following from calculations with
Gogny, Skyrme, and covariant nuclear mean-field interactions. These
interactions are successful in describing nuclear charge radii and binding
energies but predict different values for neutron skins. We perform the study
by fitting two-parameter Fermi distributions to the calculated self-consistent
neutron and proton densities. We note that the equivalent sharp radius is a
more suitable reference quantity than the half-density radius parameter of the
Fermi distributions to discern between the bulk and surface contributions in
neutron skins. We present calculations for nuclei in the stability valley and
for the isotopic chains of Sn and Pb.Comment: 13 pages, 9 figure
Density dependence of the symmetry energy from neutron skin thickness in finite nuclei
The density dependence of the symmetry energy around saturation density,
characterized by the slope parameter L, is studied using information provided
by the neutron skin thickness in finite nuclei. An estimate for L is obtained
from experimental data on neutron skins extracted from antiprotonic atoms. We
also discuss the ability of parity-violating elastic electron scattering to
obtain information on the neutron skin thickness in 208Pb and to constrain the
density dependence of the nuclear symmetry energy. The size and shape of the
neutron density distribution of 208Pb predicted by mean-field models is briefly
addressed. We conclude with a comparative overview of the L values predicted by
several existing determinations.Comment: 17 pages, 10 figures, submitted to EPJA special volume on Nuclear
Symmetry Energ
Study of the neutron skin thickness of Pb in mean field models
We study whether the neutron skin thickness of Pb
originates from the bulk or from the surface of the neutron and proton density
distributions in mean field models. We find that the size of the bulk
contribution to of Pb strongly depends on the slope
of the nuclear symmetry energy, while the surface contribution does not. We
note that most mean field models predict a neutron density for Pb
between the halo and skin type limits. We investigate the dependence of parity-
violating electron scattering at the kinematics of the PREX experiment on the
shape of the nucleon densities predicted by the mean field models for
Pb. We find an approximate formula for the parity-violating asymmetry
in terms of the central radius and the surface diffuseness of the nucleon
densities of Pb in these models.Comment: 5 pages, 2 figures, proceedings MBC 2011 - Many body correlations
from dilute to dense nuclear systems - IHP PARI
Nuclear symmetry energy and neutron skin thickness
The relation between the slope of the nuclear symmetry energy at saturation
density and the neutron skin thickness is investigated. Constraints on the
slope of the symmetry energy are deduced from the neutron skin data obtained in
experiments with antiprotonic atoms. Two types of neutron skin are
distinguished: the "surface" and the "bulk". A combination of both types forms
neutron skin in most of nuclei. A prescription to calculate neutron skin
thickness and the slope of symmetry energy parameter from the parity
violating asymmetry measured in the PREX experiment is proposed.Comment: 12 pages, 5 figures, Presented at XXXII Mazurian Lakes Conference on
Physics, Piaski, Poland, September 11-18, 201
Influence of the single-particle structure on the nuclear surface and the neutron skin
We analyze the influence of the single-particle structure on the neutron
density distribution and the neutron skin in Ca, Ni, Zr, Sn, and Pb isotopes.
The nucleon density distributions are calculated in the Hartree-Fock+BCS
approach with the SLy4 Skyrme force. A close correlation is found between the
quantum numbers of the valence neutrons and the changes in the position and the
diffuseness of the nuclear surface, which in turn affect the neutron skin
thickness. Neutrons in the valence orbitals with low principal quantum number
and high angular momentum mainly displace the position of the neutron surface
outwards, while neutrons with high principal quantum number and low angular
momentum basically increase the diffuseness of the neutron surface. The impact
of the valence shell neutrons on the tail of the neutron density distribution
is discussed.Comment: 17 pages, 14 figure
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