Recreation of Louis Slotin's deadly hands-on experiment. Public domain government image, taken from Wikipedia.
They might know the name, but nobody ever says, "I want to be like Louis Slotin when I grow up." And with good reason. Despite being fiercely intelligent, quick thinking and brave, Slotin is famous for something that nobody really wants to be famous for—namely, dying horribly. In May 1946, Slotin, a researcher on the Manhattan Project, became the second person in history to be killed by a criticality accident, the unintentional triggering of a nuclear chain reaction.
Slotin's story made it to Hollywood, fictionalized in the movie "Fat Man and Little Boy". Not everyone got such a public legacy. As the cold war neared an end in the 1980s, scientists in the USSR began to share information with their American counterparts, and, for the first time, we learned about the Soviet Slotins. Now, their legacy will shape the way emergency personnel respond to nuclear accidents and terrorism and, hopefully, make it easier to save lives…
"Criticality accident" is just a fancy way of saying "nuclear reaction happening where and when you don't want it to". It starts with fissile material–atoms whose nuclei have a tendency to split apart. Get these materials in the way of free neutrons and a neutron can enter the nucleus of an atom and rupture it. That fission releases energy, and neutrons, which cause more nuclear fissions in nearby atoms. The chain reaction keeps going and going. It will stop on its own, but only when it's good and ready—which is, to say, when a release of energy forces the fissile material apart (think: explosion), when enough of the material has been used up so that what's left no longer throws off enough neutrons to keep the reaction going, or when heat energy produced by the reaction builds up enough that it makes the atoms–which are most unstable at room temperature–less likely to split.
It's a little scary, but these accidents are extremely rare. The Los Alamos National Laboratory Review of Criticality Accidents lists only 60, worldwide, since we started playing with this stuff in the 1940s. Most didn't kill anyone. And 38 of the 60 can't even be called completely unexpected, as they occurred in research reactors and during experiments where scientists were bringing fissile materials together to gauge the point at which criticality happens.
In fact, that's what Louis Slotin was doing, slowly lowering the top half of a neutron-reflecting shell over a sphere of fissile plutonium. Today, nobody would attempt that experiment except from a safe distance. Slotin, however, was using his bare hands to hold the shell, and had a screwdriver propped in there to keep the two halves from touching. A crowd of seven colleagues was watching him work when the screwdriver slipped out, sealing the shell and launching a reaction. I call Slotin brave and quick-thinking because, instead of freaking and running, he pulled the shell apart, probably saving his coworkers' lives. He, however, died nine days later.
Slotin's story is pretty well-known. But, in Russia, similar accidents were happening that nobody knew about for decades. Like Slotin's, some these stemmed from both unfortunate chance, and decisions by the researchers that, with 20/20 hindsight, look a little silly. Why would depend on a precariously placed screwdriver to save you from certain death? Why would you try to run through a criticality experiment after normal work hours, without key safety measures in place, and with the goal of trying to be done in time to make it to the theater that evening…as two unfortunate Russian scientists did in 1968.
Other Russian accidents, though, had little to do with the people hurt–except in that those people simply didn't have enough training for the jobs they had. In 1953, two workers at Mayak, a factory that processed fissile material for experimental and military use, were exposed to a criticality accident. But neither knew enough about nuclear fission to realize that. They knew something weird had gone down, but didn't think it was a big deal. Instead, they fixed the problem and went back to work. They finished their shift and, because Mayak had no automatic criticality alarms, nobody knew anything had gone wrong at all until two days later when one of the men collapsed at work. He survived, but only after a long illness that involved the amputation of both his legs.
Neil Wald, professor emeritus at the University of Pittsburgh's department of Environmental and Occupational Health, was one of the first Americans to learn about this, and other accidents at Mayak. He studies the impact of radiation on human health and was part of a team that began working with Soviet counterparts in the 1980s to research the accidents and use them to better understand how to help people who've been exposed.
"They actually did quite a good job of keeping the medical records," he told me. "They made the accidents state secrets, so they never threw anything away. Everything we saw, all the documents, were stamped on the back with a great big seal that said, 'State secret.'"
The goal of this collaboration is to develop a way of quickly diagnosing radiation exposure, so that emergency personnel can show up at the scene of an accident and be able to tell who needs the most medical attention the fastest. Dr. Wald says the system could be used both at nuclear facilities, and by regular EMTs responding to situations where a dirty bomb has exploded, or some other intentional nuclear exposure might have happened.
Coming Friday: Criticality Accidents Part II–The Blue Flash and the Origin of Super Hero Origins!