Study Of The Synthesis Mechanism Of Superheavy Nuclei Based On The Dynamically-deformed DNS Model

A lot of researches have been carried out and great achievements have been obtained in the study of superheavy nuclei(SHN) by experimental nuclear physicists. All the superheavy elements with Z < 119 have been synthesized successfully by continuous efforts from the laboratories of GSI, JINR, RIKEN and so on. In the same time,many theoretical models, including the dinuclear system(DNS) model, have been proposed and developed to describe the synthesis mechanism of the SHN. Although theoretical cross sections agree well with known experimental data, the results from different models show big discrepancies when predicting the properties of unknown SHN. This thesis try to improve the DNS model by including dynamical deformation of both fragments.In the earlier theoretical treatments of the DNS model, it was assumed that the interacting projectile-like and target-like fragments always keep their ground-state deformations during the formation of SHN. In our opinion, to describe the formation of SHN, not only the proton and neutron numbers of both fragments, and the distance between them, but also the dynamical deformations of both fragments should be considered and coupled with other degrees of freedom. Due to strong Coulomb and nuclear interactions, the deformations of both fragments in heavy fusion reactionswould change with time and should be treated dynamically. Because of the dissipative process of large radial kinetic energy loss, the nucleons in the highly excited fragments would be distributed at many different energy levels, and it would result in considerable and irreversible deformations. Moreover, the masses of both deformed fragments,the interactions between them and the driving potential of the system would change with their deformation parameters, and these changes would then influence the dissipative process of other degrees of freedom(such as energy and angular momentum),nucleon transfer process and the inner excitation energy of the system and make the changes of deformation parameters carry on.Since the numerical calculation of master equation, which includes the proton and neutron numbers of both fragments, the distance between them, and their dynamical deformations, is very complex,the dynamical deformation has been decoupled from other degrees of freedom in our work. The evolution of dynamical deformations of both fragments has been treated as dissipative process and the analytic expression of the evolution of both fragments has been obtained by solving the corresponding Fokker-Planck equation. The dynamically-deformed DNS model has been developed by combining the evolution of dynamical deformations of both fragments with the master equation which includes the proton and neutron numbers. The following results have been obtained:(1) The evolutions of the dynamical deformations of the projectile-like and target-like fragments are mainly determined by the intrinsic structures of both fragments and the interactions between them;(2) The evolutions of the dynamical deformations of both fragments are correlated by making the driving potential of the system towards smaller directions;(3) The relaxation time of the dynamical deformations of both fragments are also influenced by the excitation energy, drift constant and isospin of the system;(4) The inner fusion barrier of the system is changed by the dynamical deformations of both fragments and thus it changes the fusion prob-ability of the compound nuclide and the cross section of the SHN.