New experimental and theoretical results for the 235U fission neutron spectrum

The prompt fission neutron spectrum (PFNS) was measured at 0.5 MeV incident neutron energy. An angular anisotropy in the prompt neutron emission was found. The neutron yield is ∼10% higher and the average energy ∼80 keV smaller at 90 degree than at 120 degree neutron emission angle. The spectral difference diminishes with increasing prompt neutron energy. The experimental data were successfully described with the semi-empirical “three sources” model.