The Scattering of Thermal Neutrons by Moderators

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Abstract
A comprehensive scheme for the analysis and use of thermal neutron scattering data is described here. Experimental work has been carried out at Chalk River with a 4-rotor high speed chopper system operated in conjunction with a multicounter multichannel neutron time-of-flight system. This apparatus allows many measurements to be made of the probability of an incident neutron of given energy to be scattered through a given angle with a given energy change. The results of such experiments are reduced to a “Scattering Law,” which is a function S of two variables (α and β) representing the momentum and energy transferred in the scattering process. Scattering Laws have been measured for many moderators at many temperatures. The scattering law can be divided into interference and self-terms; for the application to neutron spectrum calculations it is sufficient to consider the interference term as a small correction to the self-term, [in practice the interference term is calculated and subtracted from th...