Louis Slotin

January 8, 2021

By Martin Zeilig 

It happened in an instant. A sudden blue glow momentarily enveloped the room before evaporating. In that moment, as the Geiger counter clicked wildly, scientist Louis Slotin knew that he had received a lethal dose of gamma and neutron radiation from the core of the plutonium bomb he was testing. It was 3:20 P.M. on Tuesday, 21 May 1946, at the secret Omega Site Laboratory in Pajarito Canyon, Los Alamos, New Mexico.

Slotin had been instructing a colleague, Alvin C. Graves, who was to replace him at the Omega Site. Also present was S. Allan Kline, a 26-year-old graduate of the University of Chicago, who had been called over to observe the procedure. Five other colleagues were close by as Slotin, a Canadian physicist from Winnipeg who had been part of the team that created the atomic bomb, performed the action that would bring into close proximity the two halves of a beryllium-coated sphere and convert the plutonium to a critical state.

With his left thumb wedged into a cavity in the top element, Slotin had moved the top half of the sphere closer to the stationary lower portion, a micro-inch at a time. In his right hand was a screwdriver, which was being used to keep the two spheres from touching. Then, in that fatal moment, the screwdriver slipped. The halves of the sphere touched and the plutonium went supercritical.

The chain reaction was stopped when Slotin knocked the spheres apart, but deadly gamma and neutron radiation had flashed into the room in a blue blaze caused by the instantaneous ionization of the lab’s air particles. Louis Slotin had been exposed to almost 1,000 rads of radiation, far more than a lethal dose. Kline, who had been three or four feet away from Slotin, received between 90 and 100 rads, while Graves, standing a bit closer, received an estimated 166 rads.

A surge of heat “swept over the observers, felt even by those some distance from the source,” writes Thomas D. Brock, a retired University of Wisconsin biologist who has done extensive research on early atomic-era accidents at Los Alamos. “In addition to the blue glow and heat, Louis Slotin experienced a sour taste in his mouth [and] an intense burning sensation in his left hand. As soon as Slotin left the building, he vomited, a common reaction from intense radiation.” Another commentator suggests that it was as though Slotin had been fully exposed to an exploding atomic bomb at a distance of 4,800 feet.

The witnesses to the demonstration were taken to the Los Alamos hospital. Slotin vomited once prior to being examined, and several times more in the next few hours, but stopped by the next morning. His general health seemed acceptable. But his left hand, initially numb and tingling, became increasingly painful. This was the hand that had been closest to the core, and scientists later estimated that it had received more than fifteen thousand rem of low-energy X rays. Slotin’s whole-body dose was around twenty-one hundred rem of neutrons, gamma rays, and X rays. (Five hundred rem is usually fatal for humans.) The hand eventually took on a waxy blue appearance and developed large blisters. Slotin’s physicians kept it packed in ice, to limit the swelling and the pain. His right hand, which had been holding the screwdriver, suffered lesser versions of these symptoms.

Slotin called his parents, in Winnipeg, who were flown out to New Mexico on the Army’s dime. They arrived four days after the accident. On the fifth day, Slotin’s white-blood-cell count dropped dramatically. His temperature and pulse began to fluctuate. “From this day on, the patient failed rapidly,” the medical report noted. Slotin suffered nausea and abdominal pain and began losing weight. He had internal radiation burns—what one medical expert called a “three-dimensional sunburn.” By the seventh day, he was experiencing periods of “mental confusion.” His lips turned blue and he was put in an oxygen tent. Eventually, he sank into a coma. He died nine days after the accident, at the age of thirty-five. The cause was recorded as acute radiation syndrome, also known as radiation sickness. His body was shipped to Winnipeg for burial in a sealed Army casket.

Louis Slotin is buried in the family plot at the Shaarey Zedek Cemetery on North Main Street, just across from Kildonan Park.

A documentary film (with some dramatization), Tickling the Dragon’s Tail: The Story of Louis Slotin, directed by Tom Radford (produced by True North Productions and CanWest Global) was released in April 1999.


Wellerstein, Alex. “The Demon Core and the Strange Death of Louis Slotin,” The New Yorker,  May 21, 2016, https://www.newyorker.com/tech/annals-of-technology/demon-core-the-strange-death-of-louis-slotin .

Zeilig, Martin. “Dr. Louis Slotin and ‘The Invisible Killer’.” Canada’s History, July 1990.  now Canada’s History, August 28, 2016.  https://www.canadashistory.ca/explore/science-technology/dr-louis-slotin-and-the-invisible-killer Previously published in The Beaver in July 1990.