The incident involving Louis Slotin took place during a critical experiment with a subcritical mass of plutonium referred to as the 'demon core,' originally part of the Manhattan Project. On that fateful day, Slotin and several colleagues were conducting a test to determine the critical mass of the plutonium sphere. To achieve this, Slotin employed a risky technique known as the 'double-ellipsoid method,' which involved placing two hemispherical shells around the core while maintaining a delicate balance to avoid criticality. Despite his experience and the precautions taken, the safety of this method was not fully appreciated during that period.

During the experiment, Slotin slipped and the two hemispheres came together, causing a prompt critical reaction. In that brief moment, an intense blue flash of radiation was emitted—known as Cherenkov radiation. Slotin received an acute dose of radiation, estimated at about 1,000 roentgens, which was significantly above lethal levels. He exhibited symptoms of radiation sickness shortly thereafter. Despite immediate medical attention, his condition deteriorated rapidly, leading to his death just nine days later.

The Slotin incident raised significant concerns about the safety protocols in place for conducting nuclear experiments. At the time, the understanding of radiation safety was evolving, but incidents like this revealed the inherent dangers of working with fissile materials. Slotin's death prompted changes in safety practices, including the development of remote handling techniques and stricter controls over criticality experiments. The incident underscored the need for robust training in both theoretical and practical aspects of nuclear physics.