FLUCUATION-DISSIPATION DYNAMICS IN THE FUSION-FISSION REACTION OF MASSIVE NUCLEI

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We have studied various subjects concerning the fusion-fission reaction of massive nuclei from the viewpoint of fluctuation-dissipation dynamics.(1) We have studied the phenomenon of fusion hindrance in the fusion of massive nuclei with the 3-dimensional Langevin equation. We have estimated the incident energy necessary for fusion for ィイD1100ィエD1Mo+ィイD1100ィエD1Mo, ィイD1100ィエD1Mo+ィイD1110ィエD1Pd, and ィイD1110ィエD1Pd+ィイD1110ィエD1Pd systems. By using the statistical cascade code, we have estimated the evaporation residue cross section for these systems and compared them with the experiments.(2) We have studied the dynamics of the synthesis of superheavy elements with the 3-dimesional dissipative dynamical model to treat the mass-asymmetric incident channels. In 1999, there performed new experiments of the synthesis of the superheavy elements. In particular, the results of the ィイD148ィエD1Ca+ィイD1244ィエD1Pu reaction that was performed at Flerov Laboratory in Dubua, Russia is in good agreement with our theoretical prediction. In order to treat the low excitation energy experiment that was performed at Lawrence Berkeley Laboratory, USA, we have improved our calculation by taking into account of the shell correction energy from the fusion stage and the excitation energy dependence of the level density parameter that is originated from the shell correction.(3) To study systematics of the evaporation residue cross section and to predict the optimum condition for the synthesis of superheavy elements, we have parametrized the results of the dynamical calculation as functions of the incident energy, mass asymmetry, atomic and mass numbers of compound system.(4) We have utilized the mean first passage time of the Fokker-Planck equation to calculate the fission width in the case where the fission barrier is very low. We have incorporated this method in the cascade code and have estimated the survival probability against fission decay in the case of low fission barrier.