A Decay And Spontaneous Fission Within A Generalized Liquid Drop Model

The α-decay is now become a powerful tool for investigating the nuclear structure, such as the half-life,the shell effects,the nuclear spin and parity,and the nuclear deformation. Sponta-neous fission which is a much complex process,undergoes the similar quantum tunneling effect. The a-decay as well as spontaneous fission, are the most important channels which determine the lifetime of heavy and synthesized superheavy elements. The generalized liquid drop model (GLDM), which includes such a proximity energy term and the mass and charge asymmetry, has made it possible to describe the fusion, fission, cluster radioactivity and α-decay processes. The aim of this thesis is to systematically investigate a-decay and spontaneous fission barriers and half-lives of even-even heavy nuclei in the frame of the GLDM.For a-decay, many previous calculations assuming a spherical shape for both the parent and daughter nuclei have been successful to some extent, however it is more reasonable to take the deformation effects into account. The barriers between the spherical a particle and the de-formed daughter nucleus are evaluated numerically through the quasimolecular shape path. The158even-even nuclei from Z=62to Z=118are investigated to extract a particle preformation and an analytic expression for the factor of the preformation is proposed to perform accurate calculations of the a-decay half-lives and guide nuclear shell structure. Besides, experimental half-lives of some very neutron-deficient nuclei and superheavy nuclei are well produced or predicted.For spontaneous fission, the shell correction of the spherical parent nucleus is calculated by using the Strutinsky method, and a empirical shape-dependent shell correction is employed during the deformation process. A quasi-molecular shape sequence has been defined to describe the process from one-body shape to two-body shapes system, and a two-touching-ellipsoid is adopted when the superdeformed one-body system reaches the saddle point. The shell effect are taken into account during the fission process. On these basis the spontaneous fission barriers are systematically studied for nuclei from230Th to249Cm in different possible exiting channels with the different mass and charge asymmetries. It is found that at around Sn-like fragment the outer fission barriers are lower, and the preferable fission channels are distinctly pronounced.