Search for a Resonance Absorption of Neutrons in Graphite

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Abstract
The purpose of the experiment was to determine whether or not an appreciable absorption of neutrons takes place in graphite during the slowing down process. A simplified description of the experiment is as follows: A Ra-Be photo-neutron source was surrounded by a solid sphere of graphite of 11-inch radius. The graphite sphere was immersed in an essentially infinite mass of paraffin. The activities of thin indium foils due to thermal neutrons were measured as a function of distance from the source for the following two cases: (a) with the graphite sphere in place, (b) with the graphite sphere removed. From these distributions and the relative thermal neutron capture cross sections of graphite and paraffin, the relative numbers of neutrons captured as thermal neutrons in the two cases were calculated. The difference between these two numbers is a measure of the number of neutrons absorbed by the graphite sphere during the slowing down process. The results indicate that if a resonance absorption exists in graphite, then, at most, 5 percent of all neutrons passing through such a level would be absorbed by the 11-inch radius graphite sphere.

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