Quantum and statistical fluctuations in dynamical symmetry breaking

Dynamical symmetry breaking in an expanding nuclear system is investigated in semi-classical and quantum framework by employing a collective transport model which is constructed to mimic the collective behavior of expanding systems. It is shown that the fluctuations in collective coordinates during the expansion are developed mainly by the enhancement of the initial fluctuations by the driving force, and that statistical and quantum fluctuations have similar consequences. It is pointed out that the quantal fluctuations may play an important role in the development of instabilities by reducing the time needed to break the symmetry, and the possible role of quantal fluctuations in spinodal decomposition of nuclei is discussed.Comment: 19 Latex pages including 6 figure

Collisional Damping of Nuclear Collective Vibrations in a Non-Markovian Transport Approach

A detailed derivation of the collisional widths of collective vibrations is presented in both quantal and semi-classical frameworks by considering the linearized limits of the extended TDHF and the BUU model with a non-Markovian binary collision term. Damping widths of giant dipole and giant quadrupole excitations are calculated by employing an effective Skyrme force, and the results are compared with GDR measurements in Lead and Tin nuclei at finite temperature.Comment: 23 pages, 6 Figure

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

Multi-Nucleon Exchange in Quasi-Fission Reactions

Nucleon exchange mechanism is investigated in the central collisions of ${}^{40}$Ca + ${}^{238}$U and ${}^{48}$Ca + ${}^{238}$U systems near the quasi-fission regime in the framework of the Stochastic Mean-Field (SMF) approach. Sufficiently below the fusion barrier, di-nuclear structure in the collisions is maintained to a large extend. Consequently, it is possible to describe nucleon exchange as a diffusion process familiar from deep-inelastic collisions. Diffusion coefficients for proton and neutron exchange are determined from the microscopic basis of the SMF approach in the semi-classical framework. Calculations show that after a fast charge equilibration the system drifts toward symmetry over a very long interaction time. Large dispersions of proton and neutron distributions of the produced fragments indicate that diffusion mechanism may help to populate heavy trans-uranium elements near the quasi-fission regime in these collisions

Collisional Damping of Giant Monopole and Quadrupole Resonances

Collisional damping widths of giant monopole and quadrupole excitations for $^{120}$Sn and $^{208}$Pb at zero and finite temperatures are calculated within Thomas-Fermi approximation by employing the microscopic in-medium cross-sections of Li and Machleidt and the phenomenological Skyrme and Gogny forces, and are compared with each other. The results for the collisional widths of giant monopole and quadrupole vibrations at zero temperature as a function of the mass number show that the collisional damping of giant monopole vibrations accounts for about 30-40% of the observed widths at zero temperature, while for giant quadrupole vibrations it accounts for only 20-30% of the observed widths of zero temperature.Comment: RevTex, 12 pages, 6 PS figure

Quantal Extension of Mean-Field Dynamics

A method is presented for numerical implementation of the extended TDHF theory in which two-body correlations beyond the mean-field approximation are incorporated in the form of a quantal collision term. The method is tested in a model problem in which the exact solution can be obtained numerically. Whereas the usual TDHF fails to reproduce the long time evolution, a very good agreement is found between the extended TDHF and the exact solution.Comment: 22 Latex pages including 7 figure

On growth of spinodal instabilities in nuclear matter-II:asymmetric matter

As an extension of our previous work, the growth of density fluctuations in the spinodal region of charge asymmetric nuclear matter is investigated in the basis of the stochastic mean-field approach in the non-relativistic framework. A complete treatment of density correlation functions are presented by including collective modes and non-collective modes as well.Comment: 20 pages, 6 figures, Accepted by Physical Review

Nucleon exchange in heavy-ion collisions within stochastic mean-field approach

Nucleon exchange mechanism is investigated in deep-inelastic symmetric heavy-ion collisions in the basis of the Stochastic Mean-Field approach. By extending the previous work to off-central collisions, analytical expression is deduced for diffusion coefficient of nucleon exchange mechanism. Numerical calculations are carried out for ${}^{40}$Ca + ${}^{40}$Ca and ${}^{90}$Zr + ${}^{90}$Zr systems and the results are compared with the phenomenological nucleon exchange model. Also, calculations are compared with the available experimental results of deep-inelastic collisions between calcium nuclei.Comment: 8 pages, 7 figure

Collisional Effects in Isovector Response Function of Nuclear Matter at Finite Temperature

The dipole response function of nuclear matter at zero and finite temperatures is investigated by employing the linearized version of the extended TDHF theory with a non-Markovian binary collision term. Calculations are carried out for nuclear dipole vibrations by employing the Steinwedel-Jensen model and compared with experimental results for $^{120}Sn$ and $^{208}Pb$.Comment: 14 pages, RevTex, 3 PS figure