A Theoretical Study For Nuclear Fission Based On Modified 1-dimensional Langevin Stochastic Dynamics

Nuclear fission is the inverse process of synthesis of new elements?e.g.superheavy elements and nuclei far from beta stability-line?,hence some researches will be put a positive feedback on the theoretical exploration of mechanism of superheavy elements.Due to the accurate calculation about the energy surface?fission barrier in one-dimensional counterpart?is the key issues in the researches of nuclear fission,therefore the shell correction which reflects the effects of the microscopic actions must be included in the theoretical calculations.In a self-consistent sense,shell correction must contain deformation dependences.Furthermore,order to accurately describe the large scale collective deformation behavior of fission,one dimensional mass tensor must also take into account the deformation dependence.To study the effect of shell correction on the emission of prescission neutron,we choose three isotopes of ^209?213?217Fr near the neutron 126 closure-shell.When the system with 60MeV excitation energy,the shell correction with deformation dependence don't move the saddle point of ²¹⁷Fr,while the shell correction without deformation dependence push the saddle point backwards in a 0.005 deformation units.The former situation is the same for^209?213Fr.The shell correction without deformation dependence generally reduces the fission barrier,compared with the promotion behavior for the method with deformation dependence the change scale is about double of the former.In all process of nuclear fission,the shell correction doesn't influence the isotope effect of emission of prescission neutron,with the increase of excitation energy,the influence of the shell correction gradually weakened.In addition,the action is influenced by the deformation dependence of nuclear dissipation.In the fourth chapter,we focus on the effect put on the emission of prescission particle by the mass tensor.So,we choose three systems with different mass numbers and carry out our study.The results show that,with One-Body Dissipation?OBD?friction and Ignatyuk level density parameter?Ign-LDP?,the prescission multiplicities calculated within the Combined Dynamical and Statistical Model?CDSM model?which including mass tensor without deformation dependence are much than CDSM in the first stage of the fission.Besides that,there appears a relationship of mass-number for the emissions of three systems with the calculations of new model,namely,the emissions of prescission particle decrease with increasing mass number.To investigate deeply the influences of parameters,we take two kinds of nuclear dissipation?Standard Parameter Set:SPS and new OBD?to carry out comparing calculations,and we find that the results with SPS dissipation and Ign-LDP can reproduce the experiments well than another parameter sets.Considering the different parameter set will likely to reproduce the experimental data well,then we must carry out much more research work with different parameter sets,and then based on the ideas of big data analysis,study the effect of the mass tensor with deformation dependence on nuclear fission.