Effect of Photoneutrons on Thermalization Experiments in Deuterium

The neutron slowing down process is frequently studied by means of a pulsed-electron beam from a Linac impinging on a heavy metal target. The resulting pulses of photoneutrons are thermalized and the differential spectrum is measured via the time-of-flight method. If the thermalizing medium contains deuterium or beryllium, a secondary distributed photoneutron source is produced by the gamma-ray flash from the Linac. The magnitude of this secondary source in D₂O was measured by foil activation and it was shown that the effect of the secondary source can be accurately evaluated.