The investigation of fission reactions by quantum molecular dynamics model

The improved quantum molecular dynamics model incorporated with microscopic potential energy surface (ImQMD+MicPES) is used to simulate the dynamical process of thermal neutron-induced fission of ^235U. In this method, the isospin effect and dynamical fluctuation are automatically considered in the improved quantum molecular dynamics model. The shell and pair effects in the fission process are included in the microscopic potential energy surface. From the viewpoint of the motions of protons and neutrons described in this theoretical method, we obtain the dynamical process of isospin nonequilibrium, the microscopic production mechanisms of different isotopes of fission fragments and different types of separation of fission system. At the scission point of fission process, we can calculate the charge number, mass number and the deformation of fission fragments. After the decay of these fragments, the calculated isotope and mass distributions are in overall agreement with the evaluated data from ENDF/B-VIII.0. In the comparison with other theoretical methods, the mass distribution of ImQMD+MicPES is similar with that of density functional theory. By tracking back to the dynamical production process of fission fragments at the peak of isotope distributions, we find the different separation mechanisms of the fission systems producing more neutron-rich fragment ^137Te and less neutron-rich fragment ^151Nd. The difference between the mass asymmetry degree of freedom and charge asymmetry degree of freedom for the production of ^137Te occurs at near the saddle point, while the difference between mass and charge asymmetry degrees of freedom for producing ^151Nd appears after the system crossing the smallest area along microscopic potential energy surface. At scission point, the smallest deformation described by parameter β2 appears around the charge number Z=53 and neutron number N=83, which are populated around magic numbers of Z=50 and N=82. The calculation results indicate the influence of the shell effect and the dynamical effect of isospin fluctuation on the yields and deformations of fission fragments.