We have calculated the potential energy surfaces for 240Pu up to the scission point using the density functional theory with different pairing strengths to investigate the effect of pairing correlations on its fission properties. An enhancement in the pairing correlations lowers the barrier heights, isomeric state, and ridge between the symmetric and asymmetric fission valleys significantly. Moreover, it weakens the microscopic shell structure around the Fermi surface, shrinks the scission frontiers, especially for the symmetric and very asymmetric fission regions, and lifts the total kinetic energies (TKEs) for the symmetric fission region. It is also emphasized that the microscopic calculation qualitatively reproduces the trend of the distribution of the measured TKEs, especially for the positions of the peaks at and .

To study the neutron-induced fission of $^{239}$Pu, the potential energy surfaces (PESs) calculations have been performed by the zero and finite-temperature density functional theory (FT-DFT) with the Skyrme force. The changes of the least-energy fission path, the fission barrier, total kinetic energy (TKE), the scission line and mass distribution of fission fragments with the incident neutron energy are analyzed. Two different ways have been used to calculate the fission yields of the neutron-induced fission $^{239}$Pu(n,f) with different incident neutron energies, in the framework of time-dependent generator coordinate method (TDGCM). One way to calculate the fission yield of $^{239}$Pu(n,f) is to solve the collective equation of TDGCM by using the PES from the FT-DFT with the corresponding temperature. The other is using the PES from the zero-temperature DFT but adjusting the initial collective energy of the wave packet in the TDGCM to the incident neutron energy. For the cases of the lower incident neutron energies, these two methods give similar results, and could reproduce the experimental peak and width of fission fragment distribution. However, for the highest incident neutron energy considered in this study, the results from the TDGCM by using the PES from zero-temperature DFT deviate explicitly to the experimental data, but those by using the PES from TD-DFT are still close to experimental data. It might be regarded as a proof that with the increase of the incident neutron energy, the shell structure of the compound nuclei has changed explicitly so that it may not be proper to use the same PES from zero-temperature to do the fission dynamic calculation.

The influence of the neck parameter on the fission dynamics at low excitation energy is studied based on the three-dimensional Langevin approach in which the nuclear shape is described with the two-center shell model (TCSM) parametrization, and the elongation, the mass asymmetry and the fragment deformation are set to be the generalized coordinates of the Langevin equation. We first study the influence of the neck parameter on the scission configuration. We find that there is almost no obvious correlation between the neck parameter ε and the mass asymmetry η at the scission point indicating that the ε has no obvious impact on the fragment mass distribution. The elongation Z0/R0 and its correlation with the mass asymmetry η at the scission point are obviously influenced by the neck parameter ε, which has a strong effect on the total kinetic energy (TKE) distribution of fragments. The pre-neutron emission fragment mass distributions for 14 MeV n+^{233,235,238}U and ^{239}Pu are calculated and then based on these results the post-neutron emission fragment mass distributions are obtained by using the experimental data of prompt neutron emission. The calculated post-neutron emission fragment mass distributions can reproduce the experimental data well. The TKE distributions for 14 MeV n+^{235}U fission are calculated for ε=0.25,0.35,0.45, and the results show that the TKE distribution cannot be described very well for the three cases. However, the trend of the calculated TKE distribution with ε is just as that is expected from the scission configuration calculations and the results with ε=0.35 present a better agreement with the experiment data compared with the other two cases.