505 research outputs found
Thermal shape fluctuation effects in the description of hot nuclei
The behavior of several nuclear properties with temperature is analyzed
within the framework of the Finite Temperature Hartree-Fock-Bogoliubov (FTHFB)
theory with the Gogny force and large configuration spaces. Thermal shape
fluctuations in the quadrupole degree of freedom, around the mean field
solution, are taken into account with the Landau prescription. As
representative examples the nuclei Er, Dy and Hg are
studied. Numerical results for the superfluid to normal and deformed to
spherical shape transitions are presented. We found a substantial effect of the
fluctuations on the average value of several observables. In particular, we get
a decrease in the critical temperature () for the shape transition as
compared with the plain FTHFB prediction as well as a washing out of the shape
transition signatures. The new values of are closer to the ones found in
Strutinsky calculations and with the Pairing Plus Quadrupole model Hamiltonian.Comment: 17 pages, 8 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
Microscopic study of 240Pu, mean-field and beyond
The influence of exact angular-momentum projection and configuration mixing
on properties of a heavy, well-deformed nucleus is discussed for the example of
Pu240. Starting from a self-consistent model using Skyrme interactions, we
analyze the resulting modifications of the deformation energy, the fission
barrier height, the excitation energy of the superdeformed minimum associated
with the fission isomer, the structure of the lowest rotational bands with
normal deformation and superdeformation, and the corresponding quadrupole
moments and transition moments. We present results obtained with the Skyrme
interactions SLy4 and SLy6, which have slightly different surface tensions.Comment: 7 pages REVTEX4, 4 figures. accepted for publication in Phys. Rev.
Triaxial Angular Momentum Projection and Configuration Mixing calculations with the Gogny force
We present the first implementation in the plane of the
generator coordinate method with full triaxial angular momentum and particle
number projected wave functions using the Gogny force. Technical details about
the performance of the method and the convergence of the results both in the
symmetry restoration and the configuration mixing parts are discussed in
detail. We apply the method to the study of Mg, the calculated energies
of excited states as well as the transition probabilities are compared to the
available experimental data showing a good overall agreement. In addition, we
present the RVAMPIR approach which provides a good description of the ground
and gamma bands in the absence of strong mixing.Comment: 40 pages,14 figure
Shape coexistence in neutron-deficient Kr isotopes: Constraints on the single-particle spectrum of self-consistent mean-field models from collective excitations
We discuss shape coexistence in the neutron-deficient Kr72-Kr78 isotopes in
the framework of configuration mixing calculations of particle-number and
angular-momentum projected axial mean-field states obtained from
self-consistent calculations with the Skyrme interaction SLy6 and a
density-dependent pairing interaction. While our calculation reproduces
qualitatively and quantitatively many of the global features of these nuclei,
such as coexistence of prolate and oblate shapes, their strong mixing at low
angular momentum, and the deformation of collective bands, the ordering of our
calculated low-lying levels is at variance with experiment. We analyse the role
of the single-particle spectrum of the underlying mean-field for the spectrum
of collective excitations.Comment: accepted for publication in Phys. Rev.
Approximate particle number projection for finite range density dependent forces
The Lipkin-Nogami method is generalized to deal with finite range density
dependent forces. New expressions are derived and realistic calculations with
the Gogny force are performed for the nuclei Er and Er. The
sharp phase transition predicted by the mean field approximation is washed out
by the Lipkin-Nogami approach; a much better agreement with the experimental
data is reached with the new approach than with the Hartree-Fock_Bogoliubov
one, specially at high spins.Comment: 5 pages, RevTeX 3.0, 3 postscript figures included using uufiles.
Submitted to Phys. Rev. Let
Global study of quadrupole correlation effects
We discuss the systematics of ground-state quadrupole correlations of binding
energies and mean-square charge radii for all even-even nuclei, from O16 up to
the superheavies, for which data are available. To that aim we calculate their
correlated J=0 ground state by means of the angular-momentum and
particle-number projected generator coordinate method, using the axial mass
quadrupole moment as the generator coordinate and self-consistent mean-field
states only restricted by axial, parity, and time-reversal symmetries. The
calculation is performed within the framework of a non-relativistic
self-consistent mean-field model using the same non-relativistic Skyrme
interaction SLy4 and a density-dependent pairing force to generate the
mean-field configurations and mix them. (See the paper for the rest of the
abstract).Comment: 28 pages revtex, 29 eps figures (2 of which in color), 10 tables.
submitted to Phys. Rev.
On the Solution of the Number-Projected Hartree-Fock-Bogoliubov Equations
The numerical solution of the recently formulated number-projected
Hartree-Fock-Bogoliubov equations is studied in an exactly soluble
cranked-deformed shell model Hamiltonian. It is found that the solution of
these number-projected equations involve similar numerical effort as that of
bare HFB. We consider that this is a significant progress in the mean-field
studies of the quantum many-body systems. The results of the projected
calculations are shown to be in almost complete agreement with the exact
solutions of the model Hamiltonian. The phase transition obtained in the HFB
theory as a function of the rotational frequency is shown to be smeared out
with the projection.Comment: RevTeX, 11 pages, 3 figures. To be published in a special edition of
Physics of Atomic Nuclei (former Sov. J. Nucl. Phys.) dedicated to the 90th
birthday of A.B. Migda
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
Beyond the relativistic mean-field approximation: configuration mixing of angular momentum projected wave functions
We report the first study of restoration of rotational symmetry and
fluctuations of the quadrupole deformation in the framework of relativistic
mean-field models. A model is developed which uses the generator coordinate
method to perform configuration mixing calculations of angular momentum
projected wave functions, calculated in a relativistic point-coupling model.
The geometry is restricted to axially symmetric shapes, and the intrinsic wave
functions are generated from the solutions of the constrained relativistic
mean-field + BCS equations in an axially deformed oscillator basis. A number of
illustrative calculations are performed for the nuclei 194Hg and 32Mg, in
comparison with results obtained in non-relativistic models based on Skyrme and
Gogny effective interactions.Comment: 32 pages, 14 figures, submitted to Phys. Rev.
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