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The interaction of slow or C neutrons can be modified by changes in the physical parameters of the material which the neutrons are traversing. Measurements of the effect of grain size on total C neutron cross section were made on randomly-oriented poly-crystalline iron and copper. In the case of copper it was found that the total cross section decreased in an exponential manner with increase in grain size. For iron it was simply established that the total cross section was substantially smaller for the larger grain size.
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Nix et al. (1945) studied this question.
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