140 research outputs found
Theoretical calculations for precision polarimetry based on Mott scattering
Electron polarimeters based on Mott scattering are extensively used in
different fields in physics such as atomic, nuclear or particle physics. This
is because spin-dependent measurements gives additional information on the
physical processes under study. The main quantity that needs to be understood
in very much detail, both experimentally and theoretically, is the
spin-polarization function, so called analyzing power or Sherman function. A
detailed theoretical analysis on all the contributions to the effective
interaction potential that are relevant at the typical electron beam energies
and angles commonly used in the calibration of the experimental apparatus is
presented. The main contribution leading the theoretical error on the Sherman
function is found to correspond to radiative corrections that have been
qualitatively estimated to be below the 0.5% for the considered kinematical
conditions: unpolarized electron beams of few MeV elastically scattered from a
gold and silver targets at backward angles.Comment: Accepted versio
Impact of the symmetry energy on the outer crust of non-accreting neutron stars
The composition and equation of state of the outer crust of non-accreting
neutron stars is computed using accurate nuclear mass tables. The main goal of
the present study is to understand the impact of the symmetry energy on the
structure of the outer crust. First, a simple "toy model" is developed to
illustrate the competition between the electronic density and the symmetry
energy. Then, realistic mass tables are used to show that models with a stiff
symmetry energy - those that generate large neutron skins for heavy nuclei -
predict a sequence of nuclei that are more neutron-rich than their softer
counterparts. This result may be phrased in the form of a correlation: the
larger the neutron skin of 208Pb, the more exotic the composition of the outer
crust.Comment: 21 pages, 8 figures, submitted to Physical Review
New Skyrme energy density functional for a better description of the Gamow-Teller Resonance
We present a new Skyrme energy density functional (EDF) named SAMi [Phys.
Rev. C 86 031306(R)]. This interaction has been accurately calibrated to
reproduce properties of doubly-magic nuclei and infinite nuclear matter. The
novelties introduced in the model and fitting protocol of SAMi are crucial for
a better description of the Gamow-Teller Resonance (GTR). Those are, on one
side, the two-component spin-orbit potential needed for describing different
proton high-angular momentum spin-orbit splitings and, on the other side, the
careful description of the empirical hierarchy and positive values found in
previous analysis of the spin (G_0) and spin-isospin (G_0^') Landau-Migdal
parameters: 0 < G_0 < G_0^', a feature that many of available Skyrme forces
fail to reproduce. When employed within the self-consistent Hartree-Fock plus
Random Phase Approximation, SAMi produces results on ground and excited state
nuclear properties that are in good agreement with experimental findings. This
is true not only for the GTR, but also for the Spin Dipole Resonance (SDR) and
the Isobaric Analog Resonance (IAR) as well as for the non charge-exchange
Isoscalar Giant Monopole (ISGMR) and Isovector Giant Dipole (IVGDR) and
Quadrupole Resonances (IVGQR).Comment: Proceedings of the Nuclear Physics Workshop "Marie & Pierre Curie"
Kazimierz 2012. To appear in Physica Script
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
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
Theoretical study of elastic electron scattering off stable and exotic nuclei
Results for elastic electron scattering by nuclei, calculated with charge
densities of Skyrme forces and covariant effective Lagrangians that accurately
describe nuclear ground states, are compared against experiment in stable
isotopes. Dirac partial-wave calculations are performed with an adapted version
of the ELSEPA package. Motivated by the fact that studies of electron
scattering off exotic nuclei are intended in future facilities in the
commissioned GSI and RIKEN upgrades, we survey the theoretical predictions from
neutron-deficient to neutron-rich isotopes in the tin and calcium isotopic
chains. The charge densities of a covariant interaction that describes the
low-energy electromagnetic structure of the nucleon within the Lagrangian of
the theory are used to this end. The study is restricted to medium and heavy
mass nuclei because the charge densities are computed in mean field approach.
Since the experimental analysis of scattering data commonly involves
parameterized charge densities, as a surrogate exercise for the yet unexplored
exotic nuclei, we fit our calculated mean field densities with Helm model
distributions. This procedure turns out to be helpful to study the
neutron-number variation of the scattering observables and allows us to
identify correlations of potential interest among some of these observables
within the isotopic chains.Comment: 18 pages, 14 figures, revtex4; modifications in text and figure
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
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
Nuclear equation of state from ground and collective excited state properties of nuclei
This contribution reviews the present status on the available constraints to the nuclear equation of state (EoS) around saturation density from nuclear structure calculations on ground and collective excited state properties of atomic nuclei. It concentrates on predictions based on self-consistent mean-field calculations, which can be considered as an approximate realization of an exact energy density functional (EDF). EDFs are derived from effective interactions commonly fitted to nuclear masses, charge radii and, in many cases, also to pseudo-data such as nuclear matter properties. Although in a model dependent way, EDFs constitute nowadays a unique tool to reliably and consistently access bulk ground state and collective excited state properties of atomic nuclei along the nuclear chart as well as the EoS. For comparison, some emphasis is also given to the results obtained with the so called ab initio approaches that aim at describing the nuclear EoS based on interactions fitted to few-body data only. Bridging the existent gap between these two frameworks will be essential since it may allow to improve our understanding on the diverse phenomenology observed in nuclei. Examples on observations from astrophysical objects and processes sensitive to the nuclear EoS are also briefly discussed. As the main conclusion, the isospin dependence of the nuclear EoS around saturation density and, to a lesser extent, the nuclear matter incompressibility remain to be accurately determined. Experimental and theoretical efforts in finding and measuring observables specially sensitive to the EoS properties are of paramount importance, not only for low-energy nuclear physics but also for nuclear astrophysics applications
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