Demon core

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A recreation of the 1946 incident. The half-sphere is seen but core inside is not seen. Note beryllium hemisphere held up with screwdriver.

Crossroads Able, a 23-kiloton air-deployed nuclear weapon detonated on 1 July 1946 using the Demon Core.

The Demon core was the nickname given to a 6.2 kg spherical subcritical mass of plutonium that accidentally went critical on two separate instances at the Los Alamos laboratory, in 1945 and 1946. Each incident resulted in the acute radiation poisoning and subsequent death of a scientist. After these incidents, the core was referred to as the Demon core.

On August 21, 1945, the plutonium core produced a burst of ionizing radiation that irradiated Harry Daghlian, a physicist who made a mistake while working alone doing neutron reflection experiments on the core. The core was placed within a stack of neutron-reflective bricks, moving the assembly closer to criticality. Harry Daghlian, while attempting to stack another brick around the assembly, accidentally dropped one of the bricks onto the core causing the assembly to go supercritical. Despite moving the brick off the assembly quickly, Daghlian received a fatal dose of radiation.

Then on May 21, 1946, physicist Louis Slotin and other scientists were in a Los Alamos laboratory conducting an experiment that involved creating a fission reaction by placing two half-spheres of beryllium (a neutron reflector) around the same plutonium core. Slotin's hand holding a screwdriver separating the hemispheres slipped, the beryllium neutron reflector hemispheres closed, and the core went supercritical, releasing a very high dose of radiation. He quickly pulled the two halves apart, stopping the chain reaction and hence saving the lives of the others in the laboratory. Louis Slotin died 9 days later from acute radiation poisoning.

The Demon core was most likely intended to be used in another nuclear weapon against Japan^{[citation needed]}. However, The core was instead used in the ABLE test of the Crossroads series, demonstrating that the criticality experiments of Daghlian and Slotin increased the efficiency of the weapon.^[1]