Louis Alexander Slotin (1 December 1910 – 30 May 1946) was a Canadian physicist and chemist who worked on the Manhattan Project. On 21 May 1946, Slotin accidentally began a fission reaction, which released a burst of hard radiation. He received a lethal dose of radiation and died of acute radiation syndrome nine days later.
During World War II, Slotin conducted research at Los Alamos National Laboratory. He performed experiments with uranium and plutonium cores to determine their critical mass values.
Slotin was the second person to die from a criticality accident, following the death of Harry Daghlian, who had been exposed to radiation by the same core that killed Slotin. Slotin was publicly hailed as a hero by the United States government for reacting quickly and preventing his accident from killing any colleagues. He was later criticized for failing to follow protocol during the experiment. The accident and its aftermath have been dramatized in several fictional and non-fiction accounts.