LANGEVIN FLUCTUATION DISSIPATION DYNAMICS OF HOT NUCLEI - PRESCISSIONNEUTRON MULTIPLICITIES AND FISSION PROBABILITIES

We combine a dynamical (Langevin) and statistical description of heavy -ion induced fission in a model which also includes the evaporation of light particles (n, p, alpha, d, giant-dipole gamma's), and apply it systematically to the data. In the dynamical and statistical parts of our approach important modifications - as compared with the convention al approach - are introduced. In both parts the crucial role is played by the entropy, which is constructed from a deformation-dependent lev el-density parameter, and a dependence on the scission point is introd uced in the statistical-model part. The new model turns out to be fair ly universal (no input parameter is readjusted for a particular system ) and reproduces satisfactorily experimental prescission neutron multi plicities and fission probabilities for a wide range of systems and ex citation energies. We extract information on the deformation dependenc e of the level-density parameter, the nuclear friction coefficient, an d on the time scale of the fission process.