Properties of Neutron Emission in Fission Processes Induced by 20 Ne+ 159 Tb and 20 Ne+ 169 Tm Reactions Between E=8 and 16 MeV/nucleon

Neutron emission in E=8, 10, 13, and 16 MeV/nucleon {sup 20}Ne+{sup 159}Tb, {sup 169}Tm induced fission reactions has been further studied. The 4{pi} configuration of the DEMON neutron multidetector allowed a detailed investigation of the pre- and postscission properties as functions of the fission parameters. The emission of the neutrons from their respective sources was found to be isotropic to a high degree. The determination of the compound-nucleus recoil velocity and the kinetic-energy release in fission suffers from smearing due to the recoil kicks imparted by the evaporated pre- and postscission light particles. Attempts to gate on these quantities lead to biases in the emission patterns of the evaporated neutrons. Specifically, with such gates, the assumption of isotropic emission is violated and attempts to analyze such gated neutron spectra with the standard fitting technique, which assumes isotropy, lead to spurious results. All these effects are clearly illustrated in this work.