Experimental investigation of symmetric and asymmetric fission of heavy systems

Collisions of Xe+Sn in the energy range E/A = 8-29 MeV and Xe + Au at E/A = 15 MeV leading to fusion-like heavy residues are studied using the 4 INDRA multidetector. The fusion cross section was measured and shows a maximum at E/A = 18-20 MeV. A decomposition into four exit-channels characterized by the number of heavy fragments produced in central collisions has been made. Their relative yields are measured as a function of the incident beam energy. Detailed study of fission exit channel was performed. The charge distributions of fission fragments show symmetric as well as asymmetric fission component increasing with impinging energy, except at the lowest incident energy where only symmetric fission is observed. This characteristic of binary asymmetric fragmentation occurring at high energy is reported for the first time. The cross section of the two components is given. Relative velocity correlation function technique between the fission fragments and light charged particles is applied in order to estimate the primary and secondary decay contributions for symmetric and asymmetric fission. Other pertinent results of the fission mechanism will be presented. The big size of the surviving residues observed in this work should bring important information for the synthesis of super heavy elements.