Effect of transients in nuclear fission on multiplicity of prescission neutrons

Transients in the fission of highly excited nuclei are studied in the framework of the Langevin equation. Time-dependent fission widths are calculated which show that a steady flow towards the scission point is established, after the initial transients, not only for nuclei which have fission barriers but also for nuclei which have no fission barrier. It is shown from a comparison of the transient time and the fission lifetime that fission changes from a diffusive to a transient-dominated process over a certain transition region as a function of the spin of the fissioning nucleus. Multiplicities of prescission neutrons are calculated in a statistical model with as well as without a single-swoop description of fission and they are found to differ in the transition region. We, however, find that the difference is marginal and hence a single-swoop picture of fission though not strictly valid in the transition region can still be used in the statistical-model calculations