Analysis of prompt neutron anisotropies in thermal neutron fission of ²³⁵U

Prompt neutron anisotropies as a function of total fragment kinetic energy E_k have been calculated in the thermal-neutron-induced fission of ²³⁵U on the basis of neutron evaporation from fully accelerated fragments. There is a large discrepancy between the calculated and available experimental results at higher E_k. This discrepancy can be attributed to the emission of an isotropic component of prompt neutrons during the descent of the compound nucleus from saddle to scission. Although the fraction of these isotropic neutrons increases with E_k, the absolute number is almost constant as a function of E_k. The importance of the present results on the pre-scission neutrons with respect to the dynamics of the nucleus from saddle to scission is discussed.