280 research outputs found
Microscopic calculation of 240Pu scission with a finite-range effective force
Hartree-Fock-Bogoliubov calculations of hot fission in
have been performed with a newly-implemented code that uses the D1S
finite-range effective interaction. The hot-scission line is identified in the
quadrupole-octupole-moment coordinate space. Fission-fragment shapes are
extracted from the calculations. A benchmark calculation for
is obtained and compared to results in the literature. In
addition, technical aspects of the use of HFB calculations for fission studies
are examined in detail. In particular, the identification of scission
configurations, the sensitivity of near-scission calculations to the choice of
collective coordinates in the HFB iterations, and the formalism for the
adjustment of collective-variable constraints are discussed. The power of the
constraint-adjustment algorithm is illustrated with calculations near the
critical scission configurations with up to seven simultaneous constraints.Comment: 18 pages, 24 figures, to be published in Physical Review
Microscopic determination of the nuclear incompressibility within the non-relativistic framework
The nuclear incompressibility is deduced from measurements of the
Isoscalar Giant Monopole Resonance (ISGMR) in medium-heavy nuclei, and the
resulting value turns out to be model dependent. Since the considered nuclei
have neutron excess, it has been suggested that the model dependence is due to
the different behaviour of the symmetry energy in different models. To clarify
this issue, we make a systematic and careful analysis based on new Skyrme
forces which span a wide range of values for , for the value of the
symmetry energy at saturation and for its density dependence. By calculating,
in a fully self-consistent fashion, the ISGMR centroid energy in Pb we
reach, for the first time within the non-relativistic framework, three
important conclusions: (i) the monopole energy, and consequently the deduced
value of , depend on a well defined parameter related to the shape of
the symmetry energy curve and called ; (ii) Skyrme forces of the type
of SLy4 predict around 230 MeV, in agreement with the Gogny force
(previous estimates using Skyrme interactions having been plagued by lack of
full self-consistency); (iii) it is possible to build forces which predict
around 250 MeV, although part of this increase is due to our poor
knowledge of the density dependence and effective mass.Comment: 19 pages, 8 figures. Submitted to PR
Gaussian matrix elements in a cylindrical harmonic oscillator basis
We derive a formalism, the separation method, for the efficient and accurate
calculation of two-body matrix elements for a Gaussian potential in the
cylindrical harmonic-oscillator basis. This formalism is of critical importance
for Hartree-Fock and Hartree-Fock-Bogoliubov calculations in deformed nuclei
using realistic, finite-range effective interactions between nucleons. The
results given here are also relevant for microscopic many-body calculations in
atomic and molecular physics, as the formalism can be applied to other types of
interactions beyond the Gaussian form. The derivation is presented in great
detail to emphasize the methodology, which relies on generating functions. The
resulting analytical expressions for the Gaussian matrix elements are checked
for speed and accuracy as a function of the number of oscillator shells and
against direct numerical integration.Comment: 55 pages, 9 figures, Computer Physics Communications 180, 1013-1040
(2009
Solution of the Skyrme-Hartree-Fock equations in the Cartesian deformed harmonic oscillator basis. (I) The method
We describe a method of solving the nuclear Skyrme-Hartree-Fock problem by
using a deformed Cartesian harmonic oscillator basis. The complete list of
expressions required to calculate local densities, total energy, and
self-consistent fields is presented, and an implementation of the
self-consistent symmetries is discussed. Formulas to calculate matrix elements
in the Cartesian harmonic oscillator basis are derived for the nuclear and
Coulomb interactions.Comment: 26 LaTeX pages, submitted to Computer Physics Communication
Microscopic Calculation of Fission Fragment Energies for the 239Pu(nth,f) Reaction
We calculate the total kinetic and excitation energies of fragments produced in the thermal-induced fission of {sup 239}Pu. This result is a proof-of-principle demonstration for a microscopic approach to the calculation of fission-fragment observables for applied data needs. In addition, the calculations highlight the application of a fully quantum mechanical description of scission, and the importance of exploring scission configurations as a function of the moments of the fragments, rather than through global constraints on the moments of the fissioning nucleus. Using a static microscopic calculation of configurations at and near scission, we have identified fission fragments for the {sup 239}Pu (n{sub th}, f) reaction and extracted their total kinetic and excitation energies. Comparison with data shows very good overall agreement between theory and experiment. Beyond their success as a proof of principle, these calculations also highlight the importance of local constraints on the fragments themselves in microscopic calculations
Effective shell model Hamiltonians from density functional theory: quadrupolar and pairing correlations
We describe a procedure for mapping a self-consistent mean-field theory (also
known as density functional theory) into a shell model Hamiltonian that
includes quadrupole-quadrupole and monopole pairing interactions in a truncated
space. We test our method in the deformed N=Z sd-shell nuclei Ne-20, Mg-24 and
Ar-36, starting from the Hartree-Fock plus BCS approximation of the USD shell
model interaction. A similar procedure is then followed using the SLy4 Skyrme
energy density functional in the particle-hole channel plus a zero-range
density-dependent force in the pairing channel. Using the ground-state solution
of this density functional theory at the Hartree-Fock plus BCS level, an
effective shell model Hamiltonian is constructed. We use this mapped
Hamiltonian to extract quadrupolar and pairing correlation energies beyond the
mean field approximation. The rescaling of the mass quadrupole operator in the
truncated shell model space is found to be almost independent of the coupling
strength used in the pairing channel of the underlying mean-field theory.Comment: 15 pages, 5 figure
A MICROSCOPIC THEORY OF LOW ENERGY FISSION: FRAGMENT PROPERTIES
Abstract not provide
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