Researching The Mechanism Of Synthesizing Super-heavy Nucleus Based On Two-Step Model

The research of the properties of super-heavy elements (SHE) and the way of synthesizing them is an important region of nuclear physics. Resent years, as the development both of experiment technologies and theoretical models, physicists make a great progress in synthesizing super-heavy nucleus. It has been118elements in the periodic table after the discovery of117by Dubna. It is a very complicated dynamical process to synthesize SHEs, whenever the nuclear force or the reaction mechanisn both are not very clear, the competition between complete fusion and quasi-fission, and the transfer and transport of nucleons, dynamical shape evolution, shell effects and quantum dissipation and fluctuation are all affect the synthesis of SHEs. So it is important to predict the optimal projectile-target combination and incident energy theoretically. It is different to get to the center of the island of super-heavy nuclei in experiments, maybe it is need to new ways of synthesizing SHEs. So to explore new ways and new mechanism of synthesis of SHEs theoretically may be a new way out.In this thesis, the first part, i.e. chapter1, is an introduction. The next chapter2, we retrospect the theory of nuclei and super-heavy nuclei history in a briefly way. And then we introduced the resent progress of researching SHEs both in theoretical and experiment in a more detail way. In chapter three, we introduced the two step model, both the basic idea and detail. And the next chapters are the main part of my work. Chapter4is the first part, we discuss the mechanism of synthesizing SHEs by two-step model, we modified the model a bit so as to fit the research the quasi-fission (QF), and take some examples to illustrate the main characters of the mass distribution of QF. We calculate the mass distributions that238U induced reactions, and compare with the experiment data, it matches well. It is show that the quasi-fission process occurs with all angular momentum. And the mass distribution depends on the reaction energy. We also calculate the reaction of30Si+238U, it shows at high excited energy, the shell effect is occurring in the quasi-fission.We also tried to synthesize the elements of Z=119,120with48Ca and the elements Z=117～120with50Ti. We chose double magic nucleus48Ca as projectile, calculated the residue cross section of48Ca+252Es、48Ca+252Es, evaporated3and4neutrons respectively getting the largest value of0.2pb and O.lpb residue cross section of48Ca+257Fm after evaporating4neutrons.We also chose neutron magic nucleus50Ti calculated50Ti+241,243Am,50Ti+242-247Cm to synthesize117-120. The systems50Ti+241,243Am and50Ti+242-247Cm get the largest residue cross section about0.02pb after evaporating3neutrons. The systems50Ti+247,249Bk and50Ti+249-252Cf evaporated3neutrons getting the largest residue cross sections0.04pb and0.01pb respectively.