Demon Core is a sphere of Plutonium-Galium Alloy, causing 2 incident from it's radiation. The Demon Core is supposed to be the 3rd Nuclear bomb.
The first incident occured in August 21st, 1945, Haroutune Krikor Daghlian Jr. is
stacking bricks, with each brick making the assembly closer to critical point. Daghlian accidentally dropped a brick, causing the Alloy to
go critical. Daghlian receive fatal doses of radiation. Killing him 25 days later, and a guard named Private Robert J. Hemmerly, 33 years later from leukimia.
The second incident, happened at May 21st, 1946. Louis Slotin, a physicist, with 7 other personel. Conducts an experiment involving a flat-
head screwdriver. In the day the incident happened, Slotin hand slipped outward a fraction of an inch while he was lowering the
top reflector, allowing the reflector to fall into place around the core. Slotin died 9 days later from the acute radiation. Graves, a person closed to Slotin, was partially shielded from the neutron outburst. Recieving
high but not lethal level of radiation, 19 years later. Graves died from heart
failure, while it might be the radiation. His
dad also died from
heart failire. The other 6 died from either the radiation or natural causes.