Neutron pinball
The Simulation
Photons with a Bremsstrahlung energy distribution are incident upon 64 thorium cylinders which are 4 mm in dia. and 80 mm in height, and with 1 cm center-to-center spacing (see 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 its direction of travel once it leaves the simulation area. The target configuration pictured below is surrounded by a r=100cm cylinder of air(axis going into the page). All cylinders in the simulation have a height of 50 cm.
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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