The demon core caused two fatal criticality accidents at Los Alamos in 1945–1946, shaping nuclear safety protocols for decades.
Key Facts
- Core mass
- 6.2 kilograms kg
- Core diameter
- 8.9 centimeters cm
- Material
- Plutonium–gallium alloy
- First accident date
- August 21, 1945
- Second accident date
- May 21, 1946
- Core fate
- Melted down, summer 1946
By the Numbers
Location
Cause → Event → Consequence
The Manhattan Project manufactured the plutonium–gallium core in 1945 as the fissile component for a potential third atomic bomb to be used against Japan. After Japan surrendered, the core was retained at Los Alamos for criticality experiments intended to demonstrate how close the assembly could be brought to a self-sustaining nuclear chain reaction using neutron-reflective tampers.
On August 21, 1945, physicist Harry Daghlian accidentally caused the core to go critical while stacking tungsten carbide reflector blocks around it; he died of acute radiation syndrome 25 days later. On May 21, 1946, physicist Louis Slotin caused a second criticality accident by allowing a beryllium reflector hemisphere to slip, exposing himself and seven others to a burst of radiation. Slotin died nine days later.
Both fatal accidents prompted the U.S. Atomic Energy Commission and Los Alamos to overhaul hands-on criticality experiment procedures, ultimately banning the type of manual, close-contact tests the two physicists had performed. The core itself was melted down during the summer of 1946, and its plutonium was recycled into other nuclear cores.