Study The Correlation Effects Of Fission Observables For The Thermal Neutron-Induced ²³⁵U And ²³⁹Pu Reaction

Nuclear energy has become an important part of clean energy source in today's society,Nowadays almost all controllable nuclear energy sources are derived from fission energy.²³⁵U and²³⁹Pu are the most concerned nuclear fuels in the research of national defense and civil reactors in our country.They have a high reaction cross section(about 600 barns)during their fission induced by thermal neutron.Thus,the development of new nuclear energy utilization systems and nuclear devices has raised the need for higher accuracy in the Observable for thermal neutron-induced²³⁵U and²³⁹Pu Fission.The energy in fission energy consists of the excitation energy,kinetic energy of light,heavy fragments,the kinetic energy of neutrons and the energy carried by?photons and?rays.However,the kinetic energy of fission fragments accounts for more than 85%of the total fission energy,where the amount of fragments produced is measured by the yield distribution.Therefore,the correlation effect between the thermal neutron-induced²³⁵U and²³⁹Pu fissions(especially the kinetic energy distribution and yield distribution of the fission fragments)is one of the core areas of research in the field of fission.In this work,we study the formation and evolution of complementary initial fragment pairs for the thermal neutron-induced fission of²³⁵U and²³⁹Pu,and a dinuclear statistical model is proposed to study the correlation effects of the fission observables in this paper.The fission nucleus is stretched along the axis to the scission point under the effect of defor-mation energy,assuming that the initial fragment is ellipsoidal and has large deformation and high excitation energy.The kinetic energy of the fragments comes from the Coulomb interaction of the fragment pairs,and we obtain the analytical expression of the kinetic energy distribution of the fragments after a rigorous theoretical derivation.We give the empirical representation of the four-level deformation parameter?₂of the fragment shape by the statistical laws of the kinetic energy distribution and yield distribution properties of the fragments after fission.Based on the statistical laws of the experimental measurement data,we get the variation laws of the average prompt neutron kinetic energy,the average prompt?photon energy and the average prompt neutron number with the mass number of fission fragments.On this basis,the excitation energy distribution form of complementary fragments associated with deformation is given by the reaction Q values of different initial fragment pairs according to energy conservation.This provides a possibility to quantitatively study the correlation effect of debris kinetic energy and mass yield.Based on obtaining an accurate quantitative description of the kinetic energy of the fragments,a representation of the fragment excitation energy distribution with only two universal parameters related to the degree of isospin asymmetry is obtained using a simulated annealing algorithm.This provides a good description of both the fragment kinetic energy distribution and the yield distribution.It provides a basis for further understanding of the nuclear fission reaction mechanism and quantitative description of post-fission observable measurements(e.g.,fis-sion fragment yield distribution,average total kinetic energy distribution,average prompt neutron number and average prompt neutron kinetic energy,average?photons,etc.)at different incident energies.