Three-dimensional Langevin calculations of fission fragment mass-energy distribution from excited compound nuclei - art. no. 054610

A stochastic approach to fission dynamics based on three-dimensional Langev in equations was applied to calculate fission fragment mass-energy distribu tion from a number of excited compound nuclei formed in reactions induced b y heavy ions. Evaporation of prescission light particles along Langevin fis sion trajectories from the ground state of the compound nucleus to its scis sion has been taken into account using a Monte Carlo simulation technique. Inclusion of the third collective coordinate in Langevin dynamics leads to a considerable increase of the variance of the mass and the kinetic-energy distributions of fission fragments as compared with two-dimensional Langevi n calculations. A liquid-drop model with finite range of nuclear forces and a modified one-body mechanism for nuclear dissipation have been used in th e calculations. The results of the calculations are compared with the avail able experimental data. The calculations performed using the three-dimensio nal Langevin dynamics reproduce sufficiently well ail the parameters of the two-dimensional fission fragment mass-energy distribution and their depend ence on various parameters of the compound nucleus. The mean prescission ne utron multiplicities are also reproduced with good accuracy. In order to re produce simultaneously the measured prescission neutron multiplicities and the variance of the fission fragment mass-energy distribution, the reductio n coefficient of the contribution from a wail formula has to be decreased a t least by half of the one-body dissipation strength (0.25 less than or equ al tok(s)less than or equal to0.5).