Study On The Superheavy Nuclei And Symmetric System Multinucleon Transfer Reactions By Dinuclear System Model

The study of the synthesis,structure and decay of superheavy nuclei is a new topic in nuclear physics.Experimental studies have shown that superheavy nuclides can be synthesized by fusion evaporation reactions.However,the synthesis of superheavy elements or neutron-rich superheavy nuclei is still facing challenges,and more appropriate reaction mechanisms need to be explored.The multi-nuclear transfer reactions is considered as an effective way to synthesize new neutron-rich nuclei,and it is also very beneficial to understand the nucleosynthesis in the evolution of astrophysics.In this thesis,fusion evaporation reaction and multinucleon transfer reactions are studied in depth on the basis of the dinuclear system（DNS）model.This paper is divided into two parts:The first part is based on the DNS model,the synthesis of superheavy nuclei by fusion-evaporation reaction.The incident energy and reaction channel were studied to find the most suitable combination of target and incident energy.In the second part,symmetric and near-symmetric collisions are studied by multinucleon transfer reactions.It also includes the pre-equilibrium cluster particles emission.The fusion dynamics of superheavy nuclei formation is studied based on the DNS model,and the model is modified to consider the influence of collision direction on the fusion reac-tion.The Monte Carlo method is used to sample potential energy surfaces of different collision directions,at which the dinuclear system is assumed to be formed at the touching configura-tion of dinuclear fragments.The production cross sections of superheavy nuclei Cn,Fl,Lv,Ts,and Og were calculated and compared with the experimental data from Dubna,The calculated results can describe the experimental data.The evaporation residue excitation functions in the channels of pure neutrons and charged particles were systematically analyzed.It is found that the cross section of charged particle evaporation is lower than that of pure neutron evaporation because of coulomb barrier.The combinations of⁴⁴Sc、^48,50Ti、^49,51V、^52,54Cr、^58,62Fe and^62,64Ni bombarding the actinide nuclides²³⁸U,²⁴⁴Pu、²⁴⁸Cm、^247,249Bk、^249,251Cf、²⁵²Es and²⁴³Am were calculated to produce the superheavy elements with Z=119-122.We obtained that the production cross sections sensitively depend on the neutron richness of the reaction system,the isotopic target has the little effect.And the structure of the evaporation residue excitation function is related to the neutron separation energy and fission barrier of the compound nucle-us.The synthesis of new SHNs in experiments provides a good theoretical basis for selecting collision combinations.Within the framework of the dinuclear system model,the multinucleon transfer dynam-ics for nearly symmetric nuclear collisions has been investigated.The main research contents include the reaction mechanism in the systems of¹⁹⁸Pt+¹⁹⁸Pt、²⁰⁴Hg+¹⁹⁸Pt and ²⁰⁴Hg+²⁰⁸Pb was investigated at beam energies around the Coulomb barrier,such as:reaction cross section、kinetic energy distribution and angular distribution of energy dependence.It was found that the isotopic yields are enhanced with increased incident energy in the domain of proton-rich nuclides.However,the production on the neutron-rich side weakly depends on the energy.The angular distribution with the beam energy was also analyzed in the multinucleon transfer reac-tions.Projectile-like fragments were produced toward the forward-angle region with increase in incident energy.The target-like fragments manifested the opposite trend in the transfer re-actions.This provides a theoretical basis for the experimental placement of the detector.By calculating the total kinetic energy distribution of the primary fragments,we find that the distri-bution is more extensive with the increase of incident energy.Pre-equilibrium cluster emission has been studied on the basis of the multinucleon transfer reactions.To calculate the⁴⁸Ca+²³⁸U、reaction.The variation of emission probability with time,angular distribution and kinetic en-ergy distribution of the emission particles are analyzed.We find that the emission probability increases with the increase of time,and tends to be stable after a certain time.With the increase of kinetic energy,the cross section of the particle first increases and then decreases in a stepped pattern,which is similar to the results of other reactions experimentally.The angular distribu-tion shows that the emission angles of particles are concentrated at 90°around,both front and rear corners are”flat”trend.