Elastic scattering in rotating thorium plate

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Overview

11.5 MeV photons are generated uniformly on the curved face of a cylinder with a direction of travel inward and normal to the surface. Enclosed within the cylinder is a cuboid thorium target that is 4 cm high along the cylindrical axis, 0.5 mm thick, and 2 cm wide.

Result

On average, photons see a target thickness of 0.72 mm and neutrons travel though 0.54 mm of thorium before escaping. 2.5% of fission neutrons underwent a scattering event, so statistically, 95% of n-n pairs escape the target unmolested, since [math] (1-0.025)^{2}=0.95[/math].

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