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National Museum of Nuclear Science & History

The Death of Louis Slotin

A mockup of the accident that killed Louis Slotin.

For the anniversary of Manhattan Project scientist Louis Slotin’s fatal criticality accident, historian Alex Wellerstein has a discerning article in The New Yorker, The Demon Core and the Strange Death of Louis Slotin. He also published an article on his blog, The Blue Flash, with additional information he uncovered while researching the piece.

On May 21, 1946, Slotin was performing an experiment he had done several times before. He was demonstrating to his colleagues how to bring a two hemispheres of a plutonium core nearly to criticality, a dangerous experiment called “tickling the dragon’s tail.” Slotin was using a screwdriver to separate the two halves of the core – but the screwdriver slipped. For a brief but fatal moment, the two halves touched and went critical.

Slotin instantly received a lethal dose of radiation, and the other people in the room received high doses. Slotin died nine days later, after enduring the agonizing symptoms of radiation sickness. Some of the other scientists in the room suffered ill health effects from the accident, both short and long-term; in a few cases, the radiation exposure may have caused or contributed to their deaths years later.

A few months earlier, the core had claimed its first victim, Harry Daghlian, in a similar criticality accident. After Slotin’s death, the core was given a macabre nickname: the “demon core.” Wellerstein traces the fate of the demon core. Previously it been thought that the core was used in one of the nuclear tests at Operation Crossroads. However, Wellerstein uncovered documents that show the demon core “ultimately met with an anticlimactic fate: in the summer of 1946, it was melted down and recast into a new weapon.” He also notes, “After Slotin’s botched demonstration, Los Alamos halted all further criticality work.” 

Louis Slotin and Herb Lehr at the assembly of the Trinity "Gadget." The uranium tamper is on the box in front of Lehr.

The building in which the Slotin accident occurred.

Louis Slotin

Harry Daghlian