Dissipation in a wide range of mass-asymmetries

All kind of binary partitions , including the alpha and cluster decays, are treated as fission processes in a unitary manner. The whole nuclear system is characterized by some collective coordinates associated to some degrees of freedom which determine approximately the behavior of many other intrinsic variables. The decaying system provides a time dependent single-particle potential in which the nucleons move independently. The fine structure of alpha- and cluster-decays and the dissipation for fission are treated. The fine structure can be explained appealing to the Landau-Zener promotion mechanism. The single-particle diagram was obtained within the superasymmetric two-center shell model. The good agreement of the theoretical values with the experimental hindrance factors proved that the fine structure is strongly ruled by the modality in which the levels bunched initially in shells are reorganized during the decay in order to reach the final configuration. The model is improved in order to take into account the residual pairing interactions. A new set of coupled equations for the Landau-Zener effect in the superfluid model was obtained by generalizing the HFB-ones. The best trajectories and the WKB penetrabilities were obtained for three channels in the fission of 236 U: 118 Pd + 118 Pd, 102 Zr + 134 Te, 86 Se + 150 Ce. The penetrabilities are proportional to the yields in a given channel. The values of the penetrabilities obtained in this way are not consistent within the experimental data. A qualitative agreement, property already invoked in order to optimize a neutron-rich nuclei source, can be obtained only if the effective mass along the trajectory is considered approximately equal with the reduced mass. The dissipation is computed along these trajectories by using the HFB equations of motion. A interesting phenomena was found. The dissipated energy is larger for the symmetric channel and decreases for the very asymmetric channel (light fragment A=86). The dissipated energy is practically zero up to the second well and begins to increase when the second barrier is penetrated. So, dissipation appears only when the barrier is penetrated. The dissipation modifies the potential energy. If the penetrabilities are calculated again for the new potential energy, a qualitative agreement with the experimental yields is obtained. As a conclusion, the experimental distributions can be explained not only as a guided evolution of the nuclear system managed by potential energy and inertia, but also by the effect of dissipation. The dissipation is ruled by the dynamics of the system and by the reorganization of levels during the fission process. (author)