414 research outputs found
Pairing Correlations in Finite Systems: From the weak to the strong fluctuations regime
The Particle Number Projected Generator Coordinate Method is formulated for
the pairing Hamiltonian in a detailed way in the projection after variation and
the variation after projection methods. The dependence of the wave functions on
the generator coordinate is analyzed performing numerical applications for the
most relevant collective coordinates. The calculations reproduce the exact
solution in the weak, crossover and strong pairing regimes. The physical
insight of the Ansatz and its numerical simplicity make this theory an
excellent tool to study pairing correlations in complex situations and/or
involved Hamiltonians.Comment: Submitted to EPJ
A variational approach to approximate particle number projection with effective forces
Kamlah's second order method for approximate particle number projection is
applied for the first time to variational calculations with effective forces.
High spin states of normal and superdeformed nuclei have been calculated with
the finite range density dependent Gogny force for several nuclei. Advantages
and drawbacks of the Kamlah second order method as compared to the
Lipkin-Nogami recipe are thoroughly discussed. We find that the Lipkin-Nogami
prescription occasionally may fail to find the right energy minimum in the
strong pairing regime and that Kamlah's second order approach, though providing
better results than the LN one, may break down in some limiting situations.Comment: 16 pages, 8 figure
Properties of the predicted super-deformed band in ^{32}S
Properties like the excitation energy with respect to the ground state,
moments of inertia, B(E2) transition probabilities and stability against
quadrupole fluctuations at low spin of the predicted superdeformed band of
^{32}S are studied with the Gogny force D1S using the angular momentum
projected generator coordinate method for the axially symmetric quadrupole
moment. The Self Consistent Cranking method is also used to describe the
superdeformed rotational band. In addition, properties of some collective
normal deformed states are discussed.Comment: 7 pages, 3 figure
Selfconsistent calculations of fission barriers in the Fm region
The fission barriers of the nuclei 254Fm, 256Fm, 258Fm, 258No and 260Rf are
investigated in a fully microscopic way up to the scission point. The analysis
is based on the constrained Hartree-Fock-Bogoliubov theory and Gogny's D1S
force. The quadrupole, octupole and hexadecapole moments as well as the number
of nucleons in the neck region are used as constraints. Two fission paths,
corresponding to the bimodal fission, are found. The decrease with isotope mass
of the half-life times of heavy Fm isotopes is also explained.Comment: 29 pages in LaTeX including 14 figure
Unveiling the origin of shape coexistence in lead isotopes
The shape coexistence in the nuclei Pb is analyzed within the
Hartree-Fock-Bogoliubov approach with the effective Gogny force. A good
agreement with the experimental energies is found for the coexisting spherical,
oblate and prolate states. Contrary to the established interpretation, it is
found that the low-lying prolate and oblate states observed in this mass
region are predominantly characterized by neutron correlations whereas the
protons behave as spectators rather than playing an active role.Comment: 5 pages, 6 postscript figure
Nuclear Halos and Drip Lines in Symmetry-Conserving Continuum HFB Theory
We review the properties of nuclear halos and nuclear skins in drip line
nuclei in the framework of the spherical Hartree-Fock-Bogoliubov theory with
continuum effects and projection on good particle number with the Gogny force.
We first establish the position of the un-projected HFB drip lines for the two
most employed parametrizations of the Gogny force and show that the use of
finite-range interactions leads almost always to small-sized halos, even in the
least bound nuclei, which is in agreement with most mean-field predictions. We
also discuss the size of the neutron skin at the drip line and its relation to
neutron asymmetry. The impact of particle-number projection and its conceptual
consequences near the drip line are analyzed in detail. In particular, we
discuss the role of the chemical potential in a projected theory and the
criteria required to define the drip line. We show that including particle
number projection can shift the latter, in particular near closed shells. We
notice that, as a result, the size of the halo can be increased due to larger
pairing correlations. However, combining the most realistic pairing
interaction, a proper treatment of the continuum and particle number projection
does not permit to reproduce the very large halos observed in very light
nuclei.Comment: Re-submitted to Phys. Rev. C after Referee's review. Layout of
figures changed to cope with editor's requirement
An approximation in symmetry conserving configuration mixing calculations
An approximation is proposed in Beyond mean field calculations to reduce the size of the grid subtended by the generator coordinates by one order of magnitude. We show the quality of the approximation calculating the excitation energies of the titanium isotopes and the E2 transition probabilitiesThis work was supported by the Spanish Ministerio de Economía y Competitividad under contracts FPA2011-29854-C04-04, FPA2014-57196-C5-2-P and BES-2012-05940
Continuum and Symmetry-Conserving Effects in Drip-line Nuclei Using Finite-range Forces
We report the first calculations of nuclear properties near the drip-lines
using the spherical Hartree-Fock-Bogoliubov mean-field theory with a
finite-range force supplemented by continuum and particle number projection
effects. Calculations were carried out in a basis made of the eigenstates of a
Woods-Saxon potential computed in a box, thereby garanteeing that continuum
effects were properly taken into account. Projection of the self-consistent
solutions on good particle number was carried out after variation, and an
approximation of the variation after projection result was used. We give the
position of the drip-lines and examine neutron densities in neutron-rich
nuclei. We discuss the sensitivity of nuclear observables upon continuum and
particle-number restoration effects.Comment: 5 pages, 3 figures, Phys. Rev. C77, 011301(R) (2008
Angular Momentum Projection and Quadrupole Correlations Effects in Atomic Nuclei
The degrees of freedom associated with shape fluctuations and space
orientation of atomic nuclei are analyzed with effective forces and large
configuration spaces. A pedagogical theoretical introduction to the topic of
symmetries restoration broken in the mean field approach as well as to the
concept of generator coordinate is presented. We discuss global properties,
like binding energies, two neutron separation energies and quadrupole moments,
as well as spectroscopic ones like excitation energies or transition
probabilities. The analysis covers selected examples of light and heavy nuclei,
as well as some examples from the stability line to the drip lines.Comment: 34 pages, 13 figures, invited lecture at 307. WE-Heraeus-Seminar,
"Relativistic Structure Models for the Physics of Radioactive Nuclear Beams,"
May 12-16, 2003, Bad Honnef, German
Fission half-lives of super-heavy nuclei in a microscopic approach
A systematic study of 160 heavy and super-heavy nuclei is performed in the
Hartree-Fock-Bogoliubov approach with the finite range and density dependent
Gogny force with the D1S parameter set. We show calculations in several
approximations: with axially symmetric and reflexion symmetric wave functions,
with axially symmetric and non-reflexion symmetric wave functions and finally
some representative examples with triaxial wave functions are also discussed.
Relevant properties of the ground state and along the fission path are
thoroughly analyzed. Fission barriers, Q-factors and lifetimes with
respect to fission and -decay as well as other observables are
discussed. Larger configuration spaces and more general HFB wave functions as
compared to previous studies provide a very good agreement with the
experimental data.Comment: 26 pages, 15 figure
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