2,085 research outputs found
Fission modes of 256Fm and 258Fm in a microscopic approach
A static microscopic study of potential-energy surfaces within the
Skyrme-Hartree-Fock-plus-BCS model is carried out for the 256Fm and 258Fm
isotopes with the goal of deducing some properties of spontaneous fission. The
calculated fission modes are found to be in agreement with the experimentaly
observed asymmetric-to-symmetric transition in the fragment-mass distributions
and with the high- and low-total-kinetic-energy modes experimentally observed
in 258Fm. Most of the results are similar to those obtained in
macroscopic-microscopic models as well as in recent Hartree-Fock-Bogolyubov
calculations with the Gogny interaction, with a few differences in their
interpretations. In particular an alternative explanation is proposed for the
low-energy fission mode of 258Fm.Comment: 14 pages, 11 figures, 3 tables, submitted to Phys. Rev.
Ground-state properties of even-even N=Z nuclei within the Hartree-Fock-BCS and Higher Tamm-Dancoff approaches
We calculate the ground-state properties of well deformed, even-even N=Z
nuclei in the region between Ni-56 and Sn-100 within two different approaches,
focusing on the binding energy and deformation and pairing properties. First,
we employ the Hartree-Fock-BCS (HFBCS) approximation with the Skyrme effective
nucleon-nucleon interaction and discuss how the results depend on the
parameterization of the interaction and on the pairing force parameters
adjusted in various schemes to reproduce the experimental odd-even mass
differences. Then, within the Higher Tamm-Dancoff Approximation (HTDA), which
explicitly conserves the particle number, we calculate the same properties
starting from the HFBCS solutions. The HTDA treatment of the ground-state
correlations is converged within a n-particle-n-hole expansion using up to n=4
particle-hole excitations of the pair type (in the sense of Cooper pairs). We
compare the ground-state properties calculated in these two descriptions of
pairing correlations and deduce the importance of the particle-number
conservation in weak pairing regimes. Finally, we extend the HTDA calculations
so as to include the proton-neutron residual interaction and investigate the
role of proton-neutron pairing on the above ground-state properties.Comment: 12 pages, 3 figures, 11 tables, submitted to Physical Review
Global microscopic calculations of ground-state spin and parity for odd-mass nuclei
Systematic calculations of ground-state spin and parity of odd-mass nuclei
have been performed within the Hartree--Fock--BCS (HFBCS) approach and the
Finite-Range Droplet Model for nuclei for which experimental data are
available. The unpaired nucleon has been treated perturbatively, and axial and
left-right reflection symmetries have been assumed. As for the HFBCS approach,
three different Skyrme forces have been used in the particle-hole channel,
whereas the particle-particle matrix elements have been approximated by a
seniority force. The calculations have been done for the 621 nuclei for which
the Nubase 2003 data set give assignments of spin and parity with strong
arguments. The agreement of both spin and parity in the self-consistent model
reaches about 80% for spherical nuclei, and about 40% for well-deformed nuclei
regardless of the Skyrme force used. As for the macroscopic-microscopic
approach, the agreement for spherical nuclei is about 90% and about 40% for
well-deformed nuclei, with different sets of spherical and deformed nuclei
found in each model.Comment: 5 pages, 4 figures (three in color), 1 table, to be submitted to
Physical Review
Structure properties of Th and Fm fission fragments: mean field analysis with the Gogny force
The constrained Hartree-Fock-Bogoliubov method is used with the Gogny
interaction D1S to calculate potential energy surfaces of fissioning nuclei
Th and Fm up to very large deformations. The
constraints employed are the mass quadrupole and octupole moments. In this
subspace of collective coordinates, many scission configurations are identified
ranging from symmetric to highly asymmetric fragmentations. Corresponding
fragment properties at scission are derived yielding fragment deformations,
deformation energies, energy partitioning, neutron binding energies at
scission, neutron multiplicities, charge polarization and total fragment
kinetic energies.Comment: 15 pages, 23 figures, accepted for publication in Phys. Rev. C (2007
Parity restoration in the Highly Truncated Diagonalization Approach: application to the outer fission barrier of Pu
The restoration of the parity symmetry has been performed in the framework of
the Highly Truncated Diagonalization Approach suited to treat correlations in
an explicitly particle-number conserving microscopic approach. To do so we have
assumed axial symmetry and used a generalized Wick's theorem due to L\"owdin in
a projection-after-variation scheme. We have chosen the Skyrme SkM
energy-density functional for the particle-hole channel and a
density-independent delta force for the residual interaction. We have applied
this approach in the region of the outer fission barrier of the Pu
nucleus. As a result, we have shown that the fission isomeric
state is statically unstable against intrinsic-parity breaking modes, while the
projection does not affect the energy at the top of the intrinsic outer fission
barrier. Altogether, this leads to an increase of the height of the outer
fission barrier--with respect to the fission isomeric state--by about 350 keV,
affecting thus significantly the fission-decay lifetime of the considered
fission isomer
Evidence of Raleigh-Hertz surface waves and shear stiffness anomaly in granular media
Due to the non-linearity of Hertzian contacts, the speed of sound in granular
matter increases with pressure. Under gravity, the non-linear elastic
description predicts that acoustic propagation is only possible through surface
modes, called Rayleigh-Hertz modes and guided by the index gradient. Here we
directly evidence these modes in a controlled laboratory experiment and use
them to probe the elastic properties of a granular packing under vanishing
confining pressure. The shape and the dispersion relation of both transverse
and sagittal modes are compared to the prediction of non-linear elasticity that
includes finite size effects. This allows to test the existence of a shear
stiffness anomaly close to the jamming transition.Comment: 4 pages 4 figure
Einstein-Weyl structures and Bianchi metrics
We analyse in a systematic way the (non-)compact four dimensional
Einstein-Weyl spaces equipped with a Bianchi metric. We show that Einstein-Weyl
structures with a Class A Bianchi metric have a conformal scalar curvature of
constant sign on the manifold. Moreover, we prove that most of them are
conformally Einstein or conformally K\"ahler ; in the non-exact Einstein-Weyl
case with a Bianchi metric of the type or , we show that the
distance may be taken in a diagonal form and we obtain its explicit
4-parameters expression. This extends our previous analysis, limited to the
diagonal, K\"ahler Bianchi case.Comment: Latex file, 12 pages, a minor modification, accepted for publication
in Class. Quant. Gra
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