Prompt Neutron Emission fromU235Fission Fragments

A description is given of measurements of the prompt neutron emission from fission fragments of ${\mathrm{U}}^{235}$ in thermal neutron induced fission. A beam of neutrons from the AWRE research reactor HERALD induces fissions in a thin (20 μg/${\mathrm{cm}}^2$) sample of ${\mathrm{U}}^{235}$. Neutrons are detected in a large (250 liters) liquid-scintillation counter and the fragment kinetic energies are measured with gold-silicon surface-barrier counters. Distributions, showing the neutron emission from both individual fission fragments and pairs of fragments, are given as functions of both the mass of the fragment and the total kinetic energy of the pair.