The demon core was a sphere of plutonium that was involved in two fatal radiation accidents when scientists tested it as a fissile core of an early atomic bomb. It was manufactured by the Manhattan Project, the U.S. nuclear weapon development effort during World War II. It was a subcritical mass that weighed 6.2 kilograms (14 lb) and was 8.9 centimeters (3.5 in) in diameter.
A re-creation of the experiment involved in the 1945 incident. The sphere of plutonium is surrounded by tungsten carbide blocks acting as neutron reflectors.
The two physicists Harry Daghlian (center left) and Louis Slotin (center right) during the Trinity Test. Both died following supercriticality accidents involving the "demon core."
A drawing based on the above sketch
Image: Tickling the Dragons Tail
In nuclear weapon design, the pit is the core of an implosion nuclear weapon, consisting of fissile material and any neutron reflector or tamper bonded to it. Some weapons tested during the 1950s used pits made with uranium-235 alone, or as a composite with plutonium. All-plutonium pits are the smallest in diameter and have been the standard since the early 1960s. The pit is named after the hard core found in stonefruit such as peaches and apricots.
The "demon core": re-creation of the configuration used in the fatal 1945 criticality accident with a sphere of plutonium surrounded by neutron-reflecting tungsten carbide blocks.
Precision plutonium foundry mold, 1959
