FLUCTUATION-DISSIPATION DYNAMICS OF FUSIOIN REACTION IN SUPERHEAVY MASS REGION AND MULTI-MODAL FISSION REACTION

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We have studied the fusion reaction in superheavy mass region and the multi-modal fission reaction in actinide region on the basis of the fluctuation-dissipation dynamics. A multi-dimensional Langevin equation has been used for numerical calculations.The four-dimensional Langevin equation is used to study the formation of superheavy nuclei after the contact of two ions. We pointed out the importance of the neck degree of freedom in the very early stage of the contact, because it has very small inertia.We have studied the multi-modal fission of actinide nuclei. We have examined the effect of the nuclear friction coefficient in the mass and kinetic energy distribution of the fragments. We pointed out that it is important to fit several physical quantities at the same time when we derive the nuclear friction coefficient.For the approaching phase, we have calculated the capture probability taking into account of the deformation and the orientation of the two ions. We pointed out that the original strength of the surface friction that was determined in deep inelastic collision may need to be reexamined for the study of the fusion process.We have studied the properties of the Langevin equation as a stochastic differential equation (SDE). In the integration of SDE, there are several ways of interpreting the stochastic integrals, for example Ito integral and Stratonovich integral. We compared the numerical results for fusion and fission process with two interpretations.We have also performed the systematic study of the fission barrier for neutron-rich nuclei. We applied it to estimate the element abundance in r-process nucleosynthesis. We pointed out the importance of the mass-asymmetric fission process. In the actinide region where the fission process takes place, the mass-asymmetric fission is dominant and the mass division is essentially determined by the shell correction in the potential energy surface.