Nuclear Fission in Low Excitation Energy within Macroscopic-microscopic Model and Langevin Approach

Abstract

The threedimensional Langevin model was used to study the fragment mass distribution and total kinetic energy (TKE) distribution and the scission configuration in lowenergy nuclear fission, in which the potential energy surface was calculated by using the macroscopicmicroscopic model based on the twocenter shell model and the finite range liquid drop model, and the inertia tensor and the friction tensor were obtained within the WernerWheeler method and the wallandwindow model, respectively. Taking the case of 14 MeV n+235U fission as an example, the influence of the elongation deformation space on the fission fragment mass distribution and the TKE distribution was investigated, and the correlation between the elongation and the mass asymmetry at the scission point was also studied. It is found that the elongation deformation space has a significant influence on the symmetric fission channel, especially for the calculation of the TKE around the symmetric mass region, which is because that the symmetric channel corresponds to the super-long deformation for the light actinide nuclei such as U, Np, Pu and so on, so that the less elongation deformation space could block the larger elongated nuclear shapes along the Langevin trajectories. In addition, the influence of the shell damping parameter on the fission fragment mass distribution and TKE distribution and the scission configuration was studied. It is found that the shell damping parameter has a larger influence on the fragment mass distribution, and the ratio of the peak height and the valley increases with the larger shell damping parameter, due to the stronger shell effect. However, it has little influence on the TKE distribution which indicates that the strength of the shell effect has little influence on the nuclear elongation. In the last, the preneutron and postneutron fragment mass distributions for the 14 MeV n+233,235U fission were calculated, and the results agree well with the evaluated data from ENDF/BⅧ0, which shows that the present model has the power of calculating the fission fragment mass distribution quantitatively.

Keywords

• langevin model
• macroscopic-microscopic model
• fission fragment mass distribution
• total kinetic energy distribution