Nucleon drift and diffusion mechanisms in central collisions of asymmetric heavy-ions at nearbarrier energies are investigated in the framework of a stochastic mean-field approach. Expressions for diffusion and drift coefficients for nucleon transfer deduced from the stochastic mean-field approach in the semiclassical approximation have similar forms familiar from the phenomenological nucleon exchange model. The variance of fragment mass distribution agrees with the empirical formula σ 2 AA (t) = N exc (t). The comparison with the time-dependent Hartree-Fock calculations shows that, below barrier energies, the drift coefficient in the semiclassical approximation underestimates the mean number of nucleon transfer obtained in the quantal framework. Motion of the window in the dinuclear system has a significant effect on the nucleon transfer in asymmetric collisions. PACS numbers: 25.70.Hi,21.60.Jz,24.60.Ky
Dynamics of spontaneous symmetry breaking and fluctuations in the Lipkin-Meshkov-Glick model are investigated in a stochastic mean-field approach. Different from the standard mean-field, in the stochastic approach, initial state fluctuations, are incorporated. In weak coupling, the approach perfectly reproduces the exact quantal dynamics. On the other hand, for increasing coupling strength, above the symmetry breaking threshold, the approach provides description of gross properties (i.e. time averaged behavior) of the exact quantal evolution.
Employing the stochastic mean-field (SMF) approach, we develop a quantal diffusion description of the multi-nucleon transfer in heavy-ion collisions at finite impact parameters. The quantal transport coefficients are determined by the occupied single-particle wave functions of the time-dependent Hartree-Fock equations. As a result, the primary fragment mass and charge distribution functions are determined entirely in terms of the mean-field properties. This powerful description does not involve any adjustable parameter, includes the effects of shell structure and is consistent with the fluctuation-dissipation theorem of the non-equilibrium statistical mechanics. As a first application of the approach, we analyze the fragment mass distribution in 48 Ca + 238 U collisions at the bombarding energy E c.m. = 193 MeV and compare the calculations with the experimental data.
Nucleon exchange mechanism is investigated in central collisions of symmetric heavy-ions in the basis of the stochastic mean-field approach. Quantal diffusion coefficients for nucleon exchange are calculated by including non-Markovian effects and shell structure.
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.
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