Microscopic-macroscopic models for fission of extreme mass asymmetry

This Ph. D. thesis is devoted to the microscopic-macroscopic nuclear models able to describe the fission processes with high mass asymmetry. It contains a forward, a preface, four chapters, conclusions, and a reference list. The chapter one presents the pertinent research on nuclear cluster emission, both theoretical and experimental. The chapter two presents a new nuclear shape parametrization with three degrees of freedom: elongation, necking, and mass asymmetry. General features of three dimensional potential barrier behaviour are analysed for the case of high mass asymmetry for different neck geometries. The chapter number three gives the computing methods of the shell corrections adequate for the case of high mass asymmetries. A new extension of the two-center harmonic approach to the single-particle shell model in the case of high asymmetry is given. The fourth chapter is devoted to the nuclear dynamics of the decay processes in a broad range of mass asymmetry to include under the same formalism the cold fission, heavy-ion emission and alpha decay. Two original methods to obtain the likeliest fission pattern with the essential features of the three subdue processes are finally described. The methods developed in this thesis are illustrated on the case of 234 U fission with 28 Mg as cluster emission and with 100 Zr as light fission fragment. (M.I.C.). 30 Figs., 88 Refs