1,034 research outputs found
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
Electron scattering in isotonic chains as a probe of the proton shell structure of unstable nuclei
Electron scattering on unstable nuclei is planned in future facilities of the
GSI and RIKEN upgrades. Motivated by this fact, we study theoretical
predictions for elastic electron scattering in the N=82, N=50, and N=14
isotonic chains from very proton-deficient to very proton-rich isotones. We
compute the scattering observables by performing Dirac partial-wave
calculations. The charge density of the nucleus is obtained with a covariant
nuclear mean-field model that accounts for the low-energy electromagnetic
structure of the nucleon. For the discussion of the dependence of scattering
observables at low-momentum transfer on the gross properties of the charge
density, we fit Helm model distributions to the self-consistent mean-field
densities. We find that the changes shown by the electric charge form factor
along each isotonic chain are strongly correlated with the underlying proton
shell structure of the isotones. We conclude that elastic electron scattering
experiments in isotones can provide valuable information about the filling
order and occupation of the single-particle levels of protons.Comment: 13 pages; 19 figure
Nuclear Symmetry Energy: constraints from Giant Quadrupole Resonances and Parity Violating Electron Scattering
Experimental and theoretical efforts are being devoted to the study of
observables that can shed light on the properties of the nuclear symmetry
energy. We present our new results on the excitation energy [X. Roca-Maza et
al., Phys. Rev. C 87, 034301 (2013)] and polarizability of the Isovector Giant
Quadrupole Resonance (IVGQR), which has been the object of new experimental
investigation [S. S. Henshaw et al., Phys. Rev. Lett. 107, 222501 (2011)]. We
also present our theoretical analysis on the parity violating asymmetry at the
kinematics of the Lead Radius Experiment [S. Abrahamyan et al. (PREx
Collaboration), Phys. Rev. Lett. 108, 112502 (2012)] and highlight its relation
with the density dependence of the symmetry energy [X. Roca-Maza et al., Phys.
Rev. Lett. 106, 252501 (2011)].Comment: Proceedings - International Nuclear Physics Conference (INPC),
Firenze 2 - 7 June 201
Giant Quadrupole Resonances in 208Pb, the nuclear symmetry energy and the neutron skin thickness
Recent improvements in the experimental determination of properties of the
Isovector Giant Quadrupole Resonance (IVGQR), as demonstrated in the A=208 mass
region, may be instrumental for characterizing the isovector channel of the
effective nuclear interaction. We analyze properties of the IVGQR in 208Pb,
using both macroscopic and microscopic approaches. The microscopic method is
based on families of non-relativistic and covariant Energy Density Functionals
(EDF), characterized by a systematic variation of isoscalar and isovector
properties of the corresponding nuclear matter equations of state. The
macroscopic approach yields an explicit dependence of the nuclear symmetry
energy at some subsaturation density, for instance S(\rho=0.1 fm^{-3}), or the
neutron skin thickness \Delta r_{np} of a heavy nucleus, on the excitation
energies of isoscalar and isovector GQRs. Using available data it is found that
S(\rho=0.1 fm{}^{-3})=23.3 +/- 0.6 MeV. Results obtained with the microscopic
framework confirm the correlation of the \Delta r_{np} to the isoscalar and
isovector GQR energies, as predicted by the macroscopic model. By exploiting
this correlation together with the experimental values for the isoscalar and
isovector GQR energies, we estimate \Delta r_{np} = 0.14 +/- 0.03 fm for 208Pb,
and the slope parameter of the symmetry energy: L = 37 +/- 18 MeV
Experiments on reinforced brick masonry vaulted light roofs
This paper describes structural tests of thin vaults made of reinforced brick masonry. The experiments consist of concentrated loading tests of 14 full-scale laboratory vaults. These vaults are designed to include common situations such as short- to midspan length, low-mid-high rise, rigid-flexible-sliding supports, instantaneous-sustained loading, low-high strength mortar, point-line loading, central-eccentric loading, point-line supports, hinged-clamped supports, symmetric-asymmetric shape, double layer versus single layer reinforcement, and uniaxial-biaxial bending, among others. The tests mainly aim to obtain the collapse loads and to characterize the pre- and post-peak response. The results show satisfactory structural performance, both in terms of ductility and strength. Moreover, it is possible to predict the structural response with numerical models developed specifically for this purpose. Flat specimens were also tested to determine the punching shear strength of the vaults. This work is part of a larger research project aimed at promoting innovative semi-prefabrication techniques for reinforced brick masonry vaulted light roofs
Microscopic calculation of the pinning energy of a vortex in the inner crust of a neutron star
The structure of a vortex in the inner crust of a pulsar is calculated
microscopically in the Wigner-Seitz cell approximation, simulating the
conditions of the inner crust of a cold, non-accreting neutron star, in which a
lattice of nuclei coexists with a sea of superfluid neutrons. The calculation
is based on the axially deformed Hartree-Fock-Bogolyubov framework, using
effective interactions. The present work extends and improves previous studies
in four ways: i) it allows for the axial deformation of protons induced by the
large deformation of neutrons due to the appearance of vortices; ii) it
includes the effect of Coulomb exchange; iii) considers the possible effects of
the screening of the pairing interaction; and iv) it improves the numerical
treatment. We also demonstrate that the binding energy of the nucleus-vortex
system can be used as a proxy to the pinning energy of a vortex and discuss in
which conditions this applies. From our results, we can estimate the mesoscopic
pinning forces per unit length acting on vortices. We obtain values ranging
between to dyn/cm, consistent with previous findings.Comment: Paper submitted for publicatio
Garvey-Kelson Relations for Nuclear Charge Radii
The Garvey-Kelson relations (GKRs) are algebraic expressions originally
developed to predict nuclear masses. In this letter we show that the GKRs
provide a fruitful framework for the prediction of other physical observables
that also display a slowly-varying dynamics. Based on this concept, we extend
the GKRs to the study of nuclear charge radii. The GKRs are tested on 455 out
of the approximately 800 nuclei whose charge radius is experimentally known. We
find a rms deviation between the GK predictions and the experimental values of
only 0.01 fm. This should be contrasted against some of the most successful
microscopic models that yield rms deviations almost three times as large.
Predictions - with reliable uncertainties - are provided for 116 nuclei whose
charge radius is presently unknown.Comment: 4 pages and 3 figure
Possibilitats de fer selecció indirecta per producció de farratge a la varietat lancaster de blat de moro
First step in the nuclear inverse Kohn-Sham problem: From densities to potentials
Nuclear density functional theory (DFT) plays a prominent role in the understanding of nuclear structure, being the approach with the widest range of applications. Hohenberg and Kohn theorems warrant the existence of a nuclear energy density functional (EDF), yet its form is unknown. Current efforts to build a nuclear EDF are hindered by the lack of a strategy for systematic improvement. In this context, alternative approaches should be pursued and, so far, an unexplored avenue is that related to the inverse DFT problem. DFT is based on the one-to-one correspondence between Kohn-Sham (KS) potentials and densities. The exact EDF produces the exact density, so that from the knowledge of experimental or ab initio densities one may deduce useful information through reverse engineering. The idea has already been proved to be useful in the case of electronic systems. The general problem should be dealt with in steps, and the objective of the present work is to focus on testing algorithms to extract the Kohn-Sham potential within the simplest ansatz from the knowledge of the experimental neutron and proton densities. We conclude that, while robust algorithms exist, the experimental densities present some critical aspects. Finally, we provide some perspectives for future works
Pygmies, Giants, and Skins
Understanding the equation of state (EOS) of neutron-rich matter is a central
goal of nuclear physics that cuts across a variety of disciplines. Indeed, the
limits of nuclear existence, the collision of energetic heavy ions, the
structure of neutron stars, and the dynamics of core-collapse supernova all
depend critically on the nuclear-matter EOS. In this contribution I focus on
the EOS of cold baryonic matter with special emphasis on its impact on the
structure, dynamics, and composition of neutron stars. In particular, I discuss
how laboratory experiments on neutron skins as well as on Pygmy and Giant
resonances can help us elucidate the structure of these fascinating objects.Comment: Invited Talk given at the 11th International Conference on
Nucleus-Nucleus Collisions (NN2012), San Antonio, Texas, USA, May 27-June 1,
2012. To appear in the NN2012 Proceedings in Journal of Physics: Conference
Series (JPCS
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