Dynamics of fast fission and fusion-fission reactions for the systems nickel 58 and nickel 64 on lead 208 (58,64 Ni + 208 Pb)

This work deals with the study of nuclei fission dynamics from the fusion reactions of nickel 58 and 64 projectile on lead 208 target. Its continues the systematic study of the fission under the DEMON co-operation. The experiments have been carried out at SARA, Grenoble, with the neutron detector DEMON. Eleven energy levels have been investigated, from 20 to 140 MeV, above the fusion barrier. A first analysis, based on the least chi-squares, allowed to determine the pre and post-scission neutron multiplicities and the average temperature of the emitting sources. A second analysis, based on the back-tracing method, has been applied to determine the correlated distributions between the initial thermal energy available in the parent compound nuclei and the total emitted neutrons multiplicity, and between the number of pre and post-scission neutrons. Results have been analysed in the scope of the dynamical fission model CDSM. They show that the extra-push is less than 20 MeV and the extra-extra-push is not measurable by the neutrons in these systems. For the first time, a distribution of pre-scission neutrons has been compared with a dynamical model. (A.L.B.)