The Tragic Tale of the Demon Core


In 1945, a researcher working with the US Army named Harry Daghlian was performing a criticality test with a 14-pound sphere of plutonium. The plutonium sphere was the same kind of core that could be used in a nuclear bomb, and this exact sphere was intended to have been dropped on Japan.

However, following the surrender of the Japanese armed forces in 1945, the sphere was returned to researchers who intended to perform tests on the subcritical mass. Then this happened…

The Daghlian Incident

Under the guidance of researchers at the Los Alamos testing facility, Harry Daghlian was performing experiments on the core to determine what number of tungsten bricks could be placed around it to cause the core to go supercritical. While working by himself one evening and placing bricks near the core, Daghlian made a fatal error, his hand slipping as he put one final brick next to the core. This caused enough outbound neutrons to be reflected back at the core to cause it to enter a state of supercriticality.

This resulted in a bright flash of blue light that Daghlian immediately recognized as a harbinger of destruction. Moving quickly, he swatted the tungsten brick to the ground, ending the cascade of radioactive material but giving himself a fatal dose of radiation in the process.

The hands-on methodology used at the Los Alamos facility was described by physicist Enrico Fermi as “like tickling the tail of a sleeping dragon.” For Daghlian, that dragon had awoken. Only twenty-five days after the incident. Daghlian died of acute radiation poisoning. At that point in time, he held the record for the most radiation ever suffered by a human being. He wouldn’t hold the title for long.

The Slotin Incident

Following Daghlian’s death, the core was not decommissioned. Instead, the researchers at the Los Alamos facility continued to perform hands-on criticality experiments with few safety precautions. Louis Sotin, who headed the projects, began experimenting with the core by putting two beryllium half-spheres around the core and lowering the top half to a nearly closed position. Rather than using safe aluminum risers, however, Slotin manipulated the sphere halves with the head of a screwdriver held in his right hand while his left hand held the half-sphere up.

Needless to say, Slotin inevitably slipped one day during a demonstration. Losing his grip on the sphere, and with the screwdriver nearly flush between the halves, Slotin caused the beryllium sphere to close when the screwdriver blade was pushed out of the way. This caused the tell-tale blue light to emanate from the now supercritical plutonium. Slotin, thinking fast, slapped the top half of the sphere aside, paused, and commented, “Well, that does it.”

Like Daghlian, Slotin passed away from acute radiation poisoning. He was exposed to such a massive dose of radiation that he died in only nine days. It is believed that Slotin holds the record for the highest amount of radiation a human being has ever been directly exposed to. After the Slotin incident, the demon core, as it came to be known, was melted down and its material was recycled for use in other cores.