365 research outputs found
Challenges in description of heavy-ion collisions with microscopic time-dependent approaches
Important efforts have been dedicated in the past few years to describe
near-barrier heavy-ion collisions with microscopic quantum theories like the
time-dependent Hartree-Fock approach and some of its extensions. However, this
field is still facing important challenges such as the description of cluster
dynamics, the prediction of fragment characteristics in damped collisions, and
sub-barrier fusion by quantum tunnelling. These challenges are discussed and
possible approaches to solve them are presented.Comment: 13 pages, 4 figures. To appear in the special issue of Journal of
Physics G on open problems in nuclear reaction theor
Particle number fluctuations and correlations in transfer reactions obtained using the Balian-V\'en\'eroni variational principle
The Balian-V\'en\'eroni (BV) variational principle, which optimizes the
evolution of the state according to the relevant observable in a given
variational space, is used at the mean-field level to determine the particle
number fluctuations in fragments of many-body systems. For fermions, the
numerical evaluation of such fluctuations requires the use of a time-dependent
Hartree-Fock (TDHF) code. Proton, neutron and total nucleon number fluctuations
in fragments produced in collisions of two 40Ca are computed for a large range
of angular momenta at a center of mass energy E_cm=128 MeV, well above the
fusion barrier. For deep-inelastic collisions, the fluctuations calculated from
the BV variational principle are much larger than standard TDHF results, and
closer to mass and charge experimental fluctuations. For the first time,
correlations between proton and neutron numbers are determined within a quantum
microscopic approach. These correlations are shown to be larger with exotic
systems where charge equilibration occurs.Comment: Accepted for publication in Phys. Rev. Lett. New version with more
detailed comparison with experimental data and prediction for exotic beam
A new inverse quasifission mechanism to produce neutron-rich transfermium nuclei
Based on time-dependent Hartree-Fock theory, a new inverse quasifission
mechanism is proposed to produce neutron-rich transfermium nuclei, in collision
of prolate deformed actinides. Calculations show that collision of the tip of
one nucleus with the side of the other results in a nucleon flux toward the
latter. The role of nucleon evaporation and impact parameter, as well as the
collision time are discussed.Comment: 8 pages, 7 figure
TDHF investigations of the U+U quasifission process
The use of actinide collisions have been suggested as a way to produce
neutron rich isotopes of high Z nuclei. The collision dynamics of these
reactions can be studied using unrestricted time-dependent Hartree-Fock (TDHF)
calculations. Here, we report on the recent studies of quasifission for the
U+U system.Comment: Presented at the XXXV Mazurian Lakes Conference on Physics, Piaski,
Poland, September 3-9, 2017
Formation and dynamics of fission fragments
Although the overall time-scale for nuclear fission is long, suggesting a
slow process, rapid shape evolution occurs in its later stages near scission.
Theoretical prediction of the fission fragments and their characteristics are
often based on the assumption that the internal degrees of freedom are
equilibrated along the fission path. However, this adiabatic approximation may
break down near scission. This is studied for the symmetric fission of
Fm. The non-adiabatic evolution is computed using the
time-dependent Hartree-Fock method, starting from an adiabatic configuration
where the fragments have acquired their identity. It is shown that dynamics has
an important effect on the kinetic and excitation energies of the fragments.
The vibrational modes of the fragments in the post-scission evolution are also
analyzed.Comment: 5 pages, 4 figures. Accepted for publication in Phys. Rev. C - Rapid
Communitatio
Isospin coupling in time-dependent-mean-field theories and decay of isovector excitations
We show that isospin non-diagonal terms should appear in the mean field
Hamiltonian when neutron-proton symmetry is broken. They give rise to charge
mixing in the single-particle wave-functions. We study the Time Dependent
Hartree-Fock response of a charge-exchange excitation which generates a charge
mixing in Ca isotopes. We find an enhancement of the low energy proton emission
in neutron-rich isotopes interpreted in terms of a charge oscillation below the
barrier.Comment: 4 pages, 3 figure
Particle transfer reactions with the time-dependent Hartree-Fock theory using a particle number projection technique
A particle-number projection technique is used to calculate transfer
probabilities in the O+Pb reaction below the fusion barrier. The
time evolution of the many-body wave function is obtained with the
time-dependent Hartree-Fock (TDHF) mean-field theory. The agreement with
experimental data for the sum of the proton-transfer channels is good,
considering that TDHF has no parameter adjusted on reaction mechanism. Some
perspectives for extensions beyond TDHF to include cluster-transfers are
discussed.Comment: Ref. 30 update
Time-dependent mean-field investigations of the quasifission process
We demonstrate that the microscopic Time-dependent Hartree-Fock (TDHF) theory
provides an important approach to shed light on the nuclear dynamics leading to
the formation of superheavy elements. In particular, we discuss studying
quasifission dynamics and calculating ingredients for compound nucleus
formation probability calculations. We also discuss possible extensions to TDHF
to address the distribution of observables.Comment: Proceedings of a talk given at FUSION17, Hobart, Tasmania, AU (20-24
February, 2017
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
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