Dynamical approach to heavy-ion induced fission using actinide target nuclei at energies around the Coulomb barrier

摘要

In order to describe heavy-ion fusion reactions around the Coulomb barrierwith an actinide target nucleus, we propose a model which combines thecoupled-channels approach and a fluctuation-dissipation model for dynamicalcalculations. This model takes into account couplings to the collective statesof the interacting nuclei in the penetration of the Coulomb barrier and thesubsequent dynamical evolution of a nuclear shape from the contactconfiguration. In the fluctuation-dissipation model with a Langevin equation,the effect of nuclear orientation at the initial impact on the prolatelydeformed target nucleus is considered. Fusion-fission, quasi-fission and deepquasi-fission are separated as different Langevin trajectories on the potentialenergy surface. Using this model, we analyze the experimental data for the massdistribution of fission fragments (MDFF) in the reactions of$^{34,36}$S+$^{238}$U and $^{30}$Si+$^{238}$U at several incident energiesaround the Coulomb barrier. We find that the time scale in the quasi-fission aswell as the deformation of fission fragments at the scission point aredifferent between the $^{30}$Si+$^{238}$U and $^{36}$S+$^{238}$U systems,causing different mass asymmetries of the quasi-fission.