[en] The theoretical part and some results obtained from a model realised for fission processes in wide range of mass-asymmetries are presented. The fission barriers are computed in a tridimensional configuration space using the Yukawa - plus - exponential macroscopic energies corrected within the Strutinsky procedure. It is assumed that channel probabilities are proportional with Gamow penetrabilities. The model is applied for the disintegration of the ²³⁹U in order to determine the relative yields for the production of neutron rich nuclei at diverse intermediate energies. (author)

No abstract available

[en] An estimation of the total number of fission events is presented for different converter-target geometries. The secondary neutron yields obtained in the converter are simulated within a phenomenological model based on Serber's formalism. (author)

[en] A two center parametrization with a smoothed neck describes the shapes during the fission process of ²³⁴ U in a wide range of mass asymmetry: alpha-decay, ²⁸ Mg radioactivity and cold fission with light fragment ¹⁰⁰ Zr. Effective inertias are calculated within the Werner-Wheeler approximation. The deformation dependent terms of the nuclear potential energy are dealt with the formalism of binary systems with different charge densities. A numerical procedure is used to find the minimum of the action integral in the overlapping region of the fission process. (Author)

[en] The single particle levels for the heavy-ion emission process are computed. This decay mode is treated like a superasymmetric fission process. The nuclear shape parametrization is characterized by three degrees of freedom. The difficulties encountered in the microscopic determination of the energy scheme at these very large mass asymmetries are presented. Thereby, a new version of the two-center model, especially designed for very large mass asymmetries, is described. The ¹⁴C heavy-ion spontaneous emission from the parent nucleus ²²³Ra is treated in the frame of this model. The principal trends of the variations obtained for the energetic levels during this superasymmetric nuclear decay are discussed. Mainly, for this kind of decay mode, the levels with lower values of the angular momentum projection Ω show more pronounced variations than those with higher Ω. Also, a qualitative explanation for the favoring of the first excited states in the fine structure in this radioactive process is given. copyright 1996 The American Physical Society

[en] The dissipation energy is computed using the microscopic time-dependent equations of motion along minimal action trajectories for three different values of the mass-asymmetries in the ²³⁶U fission. The single-particle level schemes are given by the two-center shell model. A qualitative agreement with the experimental mass distribution was obtained when the dissipation energy was taken into consideration in computing the penetrabilities

[en] A fine structure in the ¹⁴C decay of ²²⁵Ac is predicted quantitatively by accounting dynamical aspects during the disintegration process. Transitions to the excited states of the daughter nucleus are considered to be mainly directed by the Landau-Zener promotion mechanism in the region of avoided crossing levels. The level scheme is evaluated with the superasymmetric two-center shell model. The half-lives are computed considering the cluster decay as a superasymmetric fission process. (orig.)

[en] The deuteron break-up process in a suitable converter gives rise to intense neutron beams. A source of neutron rich nuclei based on the neutron induced fission can be realised using these beams. A theoretical optimization of such a facility as a function of the incident deuteron energy is reported. The model used to determine the fission products takes into account the excitation energy of the target nucleus and the evaporation of prompt neutrons. Results are presented in connection with a converter-target specific geometry. (authors)

[en] The intrinsic energy partition between the 2 complementary fission fragments is investigated microscopically. The intrinsic excitation energy of fission fragments is dynamically evaluated in terms of the time-dependent pairing equations. These equations are corroborated with 2 conditions. One of them fixes the number of particles and the other one separates the pairing active spaces associated with the 2 fragments in the vicinity of the scission configuration. The excitation energy in a wide distribution of fission fragments is calculated for the ²³⁴U parent nucleus. It is not possible to extract directly the energy partition from experimental data. Nevertheless, the main de-excitation process is the neutron evaporation. Therefore, indirect information can be obtained from neutron multiplicities, for which accurate results are available in literature. The excitation energy of each fragment can be computed and it is shown that several experimental features are reproduced by theoretical data. The deeply minimum in the neutron multiplicity occurs close to the mass of the doubly magic nucleus ¹³²Sn. A maximal value of the neutron multiplicity is obtained for the mass 116, that is in the symmetric fission region. In general, the excitation energy of the light fragment is larger than that of the heavy one. As for neutron multiplicities, excepting the strong fluctuations related to the large mass asymmetries, the results agree qualitatively well with the experimental data. It is a first microscopic description of the intrinsic energy partition in a wide range of fission channels that succeed to reproduce the main behavior of the neutron multiplicities

[en] Experimental results concerning neutron distributions from thick Be and U targets bombarded by deuterons at 200 MeV incident energies and from a thick C target bombarded by ³⁶Ar at 95 MeV/u are reported. The measurements were performed with the activation technique using an improved set of detectors. A comparison was carried out with theoretical results in the framework of the Serber model for deuteron beams and using a schematic fireball model for Ar beams