566 research outputs found
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
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.
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
Theoretical Uncertainty Quantification for Heavy-ion Fusion
Despite recent advances and focus on rigorous uncertainty quantification for
microscopic models of quantum many-body systems, the uncertainty on the
dynamics of those systems has been under-explored. To address this, we have
used time-dependent Hartree-Fock to examine the model uncertainty for a
collection of low-energy, heavy-ion fusion reactions. Fusion reactions at
near-barrier energies represent a rich test-bed for the dynamics of quantum
many-body systems owing to the complex interplay of collective excitation,
transfer, and static effects that determine the fusion probability of a given
system. While the model uncertainty is sizable for many of the systems studied,
the primary contribution comes from ill-constrained static properties, such as
the neutron radius of neutron-rich nuclei. These large uncertainties motivate
the use of information from reactions to better constrain existing models and
to infer static properties from reaction data.Comment: 6 pages, 5 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
Comparison of fission and quasi-fission modes
Quantum shell effects are known to affect the formation of fragments in
nuclear fission. Shell effects also affect quasi-fission reactions occurring in
heavy-ion collisions. Systematic time-dependent Hartree-Fock simulations of
50Ca+176Yb collisions show that the mass equilibration between the fragments in
quasi-fission is stopped when they reach similar properties to those in the
asymmetric fission mode of the 226Th compound nucleus. Similar shell effects
are then expected to determine the final repartition of nucleons between the
nascent fragments in both mechanisms. Future experimental studies that could
test these observations are discussed.Comment: 8 pages, 4 figures, 1 tabl
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