Louis Slotin (Dec 1, 1910 - May 30, 1946) was a Canadian chemist and physicist, who died as a result of a criticality accident at Los Alamos.

He was educated at the University of Manitoba, and at the University of London, where he received his PhD. He joined the Manhattan Project after visiting the University of Chicago in 1942, moving from Chicago, to Oak Ridge, Tennessee, and then to Los Alamos, New Mexico. He was part of the team that assembled the core of the Trinity device, and continued working at the Lab after the war ended.

On May 21, 1946, he was teaching several colleagues how to assemble the core of an atomic bomb in a workshop in Los Alamos. Two halves of a beryllium neutron reflector surrounding a plutonium sphere were placed above each other on a work bench, separated by a screwdriver. At some point, the screwdriver slipped, and the two halves of the reflector fell together, initiating a chain reaction in the plutonium. The assembly released a wave of heat, and the scientists observed the blue glow of Cherenkov radiation around it. Slotin was standing right next to the assembly, and knocked it apart to save his colleagues and prevent a meltdown. None of the other scientists in the room were adversely affected, but Slotin received a fatal dose, equivalent to being exposed to a nuclear blast at a distance of less than one mile. He died nine days later of acute radiation sickness. His body was returned to Canada, and was buried in his hometown of Winnipeg.

As a result of this accident and others, the Atomic Energy Commission developed procedures to assemble nuclear weapons components with remote controlled, isolated machinery.

Accident details from www.fas.org.