1,494 research outputs found
Microscopic DC-TDHF study of heavy-ion potentials and fusion cross sections
We study heavy-ion fusion reactions at energies near the Coulomb barrier, in
particular with neutron-rich radioactive ion beams. Dynamic microscopic
calculations are carried out on a three-dimensional lattice using the
Density-Constrained Time-Dependent Hartree-Fock (DC-TDHF) method. New results
are presented for the Sn+Ca system which are compared to
Sn+Ca studied earlier. Our theoretical fusion cross-sections
agree surprisingly well with recent data measured at HRIBF. We also study the
near- and sub-barrier fusion of O on C which is important to
determine the composition and heating of the crust of accreting neutron stars.Comment: Talk given by . Volker E. Oberacker 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
Equilibration dynamics and isospin effects in nuclear reactions
We discuss equilibration times and isospin effect for various quantities in
low-energy heavy-ion reactions. These include equilibration of mass, isospin,
and total kinetic energy (TKE) in quasifission and deep-inelastic reactions.
The calculations are performed using the time-dependent Hartree-Fock theory.
The influence of shell effects on the equilibration times are also discussed in
the context of theoretical and experimental results.Comment: 7 pages, 5 figures, proceedings of IWM-EC201
Neutron Transfer Dynamics and Doorway to Fusion in Time-Dependent Hartree-Fock Theory
We analyze the details of mass exchange in the vicinity of the Coulomb
barrier for heavy-ion collisions involving neutron-rich nuclei using the
time-dependent Hartree-Fock (TDHF) theory. We discuss the time-dependence of
transfer and show that the potential barriers seen by individual
single-particle states can be considerably different than the effective barrier
for the two interacting nuclei having a single center-of-mass. For this reason
we observe a substantial transfer probability even at energies below the
effective barrier.Comment: 6 pages, 9 figure
Effect of Pauli repulsion and transfer on fusion
The effect of the Pauli exclusion principle on the nucleus-nucleus bare
potential is studied using a new density-constrained extension of the
Frozen-Hartree-Fock (DCFHF) technique. The resulting potentials exhibit a
repulsion at short distance. The charge product dependence of this Pauli
repulsion is investigated. Dynamical effects are then included in the potential
with the density-constrained time-dependent Hartree-Fock (DCTDHF) method. In
particular, isovector contributions to this potential are used to investigate
the role of transfer on fusion, resulting in a lowering of the inner part of
the potential for systems with positive Q-value transfer channels.Comment: Proceedings of an invited talk given at FUSION17, Hobart, Tasmania,
AU (20-24 February, 2017
Timescales of quantum equilibration, dissipation and fluctuation in nuclear collisions
Understanding the dynamics of equilibration processes in quantum systems as
well as their interplay with dissipation and fluctuation is a major challenge
in quantum many-body theory. The timescales of such processes are investigated
in collisions of atomic nuclei using fully microscopic approaches. Results from
time-dependent Hartree-Fock (TDHF) and time-dependent random-phase
approximation (TDRPA) calculations are compared for 13 systems over a broad
range of energies. The timescale for full mass equilibration
(s) is found to be much larger than timescales for
neutron-to-proton equilibration, kinetic energy and angular momentum
dissipations which are on the order of s. Fluctuations of mass
numbers in the fragments and correlations between their neutron and proton
numbers build up within only a few s. This indicates that dissipation
is basically not impacted by mass equilibration, but is mostly driven by the
exchange of nucleons between the fragments.Comment: Letter: 6 pages, 5 figures. Supplemental material (tables): 18 pages.
Accepted for publication in Phys. Rev. Let
Cluster model of 12C in density functional theory framework
We employ the constrained density functional theory to investigate cluster
phenomena for the C nucleus. The proton and neutron densities are
generated from the placement of three He nuclei (alpha particles)
geometrically. These densities are then used in a density constrained
Hartree-Fock calculation that produces an antisymmetrized state with the same
densities through energy minimization. In the calculations no \textit{a priori}
analytic form for the single-particle states is assumed and the full energy
density functional is utilized. The geometrical scan of the energy landscape
provides the ground state of C as an equilateral triangular
configuration of three alphas with molecular bond like structures. The use of
the nucleon localization function provides further insight to these
configurations. One can conclude that these configurations are a hybrid between
a pure mean-field and a pure alpha particle condensate. This development could
facilitate DFT based fusion calculations with a more realistic C ground
state.Comment: 8 pages, 4 figures, to be published in Phys. Rev.
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