The Demon Core The name “Demon Core” sounds like something out of a B horror movie, and it should. The Demon Core was a nuclear device with a rather troublesome tendency to kill researchers. At the Los Alamos labs in the the Demon Core was a.
A sphere of Plutonium surrounded by neutron-reflecting blocks of Tungsten carbide. A re-creation of the August 1945 criticality accident at Los Alamos to measure the radiation produced when an extra block was added, making the mass supercritical.