On Alpha of ²³⁵U for Sub-thermal Neutron Energies

Abstract

An experiment to measure the capture to fission ratio α of ²³⁵U in the sub-thermal neutron energy region, is described. The experiment is based on the measurement of specific low energy capture y-rays and prompt fission γ-rays with a Ge detector. The liquid methane moderator of the Geel linac is used. as a pulsed source of sub-thermal neutrons, the neutron energy being determined by time-of-flight. The method requires that the relative yields of the measured y-rays per capture and fission event, respectively, do not vary over the energy range considered. Resultant α-values show an increase by about 9% in the subthermal region as compared to thermal energy, corresponding to a 1.2% decrease in η.