Neutron pinball
The Simulation
Photons with a Bremsstrahlung energy distribution are incident upon 64 thorium cylindrical targets. All thorium targets have 1 cm center-to-center spacing, a dia. of 0.4 cm, and a height of 8 cm. The target geometry is shown the neutron flux plot below. Photofission neutrons were simulated using the MCNPX ACE model. Upon the creation of a neutron, its initial direction of travel is logged and compared with the direction of travel as seen by a detector 150 cm away from the target. The target is surrounded by a cylindrical volume of air with a radius of 150cm and a height equal to the vertical extent of the detectors (76cm).
Results
14.5% of neutrons scattered in the thorium cylinders alone, and 16.5% scattered when air was included. The histogram below shows that if a neutron did scatter, it most likely did so at an unacceptable angle.
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