Decay processes in a wide range of mass-asymmetries with an application: optimization of a radioactive isotope source

The main goal is the analysis of nuclear fission in a wide range of mass-asymmetries, at low and medium energies. Recently, a new method was proposed by the authors to approach the fine structure phenomenon of cluster- and alpha-decays in odd-nuclei. These decays modes are considered as superasymmetric fission processes. Assuming the existence of few collective variables, associated to some generalized coordinates describing the nuclear shape parametrization, this approach allows to handle approximately the behavior of many other intrinsic variables. The single particle level scheme and the potential barrier are determined for each values of the shape generalized coordinates. During the whole process and after the decay, the single particle occupation probabilities of the orbitals of interest are computed using the Landau-Zener promotion mechanism alone. This method was successfully used to describe the 14 C- and alpha-decays. Despite the overlook of residual interactions, the agreement obtained with data gives a strong experimental support to the formalism. Our formalism gives the best agreement with the experimental results among all the studies found in the literature. Using our superasymmetric two center shell model, we developed the fission models in order to realise an exploratory analysis of a neutron rich ion source. A neutron rich nuclei source can be conceived by using the neutron induced fission process. A high neutron flux can be obtained through the deuteron break-up reaction in the so-called converters. The number of fission events and their isotopic distributions produced in an uranium target depends on the deuteron incident beam energy, the characteristics of the converter, and the geometry of the combination. These distributions are of crucial importance because they direct the isotopic distributions of the nuclear fragments (through the excitation energy of the compound nucleus) and the yields in the uranium target. To study the feasibility of such a source, the fission in a large range of mass-asymmetries must be studied in order to improve the actual models in order to obtain the isotopic distribution of nuclear fragments. To optimise the combination, several theoretical approaches were analysed. The initial kinetic energy of the deuteron beam, the nature of the converter and its geometry determines the angular and energy distributions of the emerging neutrons. The models used to simulate these distributions are essentially based on the Serber's approximation. The fission is treated in a microscopic-macroscopic approach using the two center shell model. A new concept is used to determine the isotopic distribution of the fission fragments as function of the neutron energy. A sudden dumping of the neutron energy is produced in the compound nucleus which modifies the two humped fission barrier and produces changes of the penetrability associated to each binary partition and therefore, in the isotopic distribution. The best deuteron energy required in order to produce the largest yields of neutron rich fragments produced through fission will be deduced. (authors)