(1994 - 1997) PH.D. STUDIES

In the framework of the double-humped fission barrier model, the decay characteristics of heavy excited nuclei have been analysed, demonstrating that the existence of quasi stationary excited states in the second well of heavy fissionable nuclei can greatly influence the fission dynamics and produces the result that the partial decay probabilities and the time dependence of decay yields are strongly depending on the decay mode.
In order to observe these effects, the competition between fission and emission of evaporated light particles has been studied measuring fission decay times of nuclei produced in the fusion of protons, deuterons and alpha-particles with ²³²Th and ^235,238U targets followed by emission of one or two neutrons (see A. Lamberto et al., Journal Phys. G. Nucl. Part. Physics 21 (1995) 1243).
It has been also studied the influence of kinetic energy dissipation in the fission mode on the probability of populating the second well states, using the fission diffusion model based on the Fokker-Planck equation, which permits to take the nuclear dissipation phenomenon into account.
Information on the probability of populating the second well states is useful for the study of the emission of light particles from the excited nucleus in the states of the second well, expecially in the cases where is enhanced the average number of the emitted light particles for fission event.