Science & Technology

The Plutonium "Demon Core" Killed Two Physicists Without Ever Exploding

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After the end of World War II, research on nuclear weapons continued at the top-secret Los Alamos Laboratories in New Mexico. Over the course of just under a year, a nuclear core of plutonium had claimed the lives of two physicists and sparked radical change in how nuclear research was undertaken.

Tickling the Dragon's Tail

The date was August 21, 1945. Just a week earlier, Japan had surrendered to the Allies, ending World War II. While the world and the citizens of Japan were still reeling from the show of force demonstrated at Hiroshima and Nagasaki, tucked away in a secret building complex just outside of Los Alamos, New Mexico, scientists continued their testing of nuclear weapons.

Inside of one laboratory sat a spherical mass of radioactive plutonium weighing 14 pounds (6.4 kilograms) and measuring 3.5 inches (9 centimeters) in diameter. Before the surrender of Japan, it was slated to be used in a third atomic bombing. Although the radioactive sphere was no longer needed for use in the war, scientists and researchers at Los Alamos were allowed to continue testing on the object to further the United States' understanding of nuclear weapons.

When a nuclear bomb explodes, its radioactive core goes supercritical, setting off an atomic chain reaction that releases massive amounts of energy without intervention, eventually accelerating into an atomic explosion. Researchers knew how to trigger these reactions — for the bombings in Japan, they used smaller explosives to help the core reach critical mass — but they wanted to learn more about the exact point that a core went critical. One of the ways of testing this was to surround the radioactive core with reflective materials that would make neutrons within it bounce back on themselves until the core went critical, then measure that point. That's exactly what researchers were testing on the night of August 21.

The First Incident

Renowned physicist Harry Daghlian had entered the lab alone, only accompanied by a security guard, to do research on the plutonium core. He was using tungsten carbide bricks to build a reflective shield around the core. Suddenly, Daghlian accidentally dropped one of the bricks on top of the core, causing it to go supercritical in an instant. A blue light filled the room and Daghlian was shrouded in a lethal dose of radiation. He managed to move the brick off of the assembly, stopping the reaction, but it was too late. 25 days later, he died of radiation poisoning. The security guard's exposure was much less than Daghlian's and he survived the incident, living to the ripe old age of 62.

This plutonium core, which was then known as "Rufus" and would later become known as the "demon core," had just caused the death of one of the world's best physicists. A review of the incident sparked changes in laboratory protocols, but testing on the demon core continued. Daghlian's colleagues continued testing, using the core to help further nuclear research for another nine months with no further incidents. That is, until May 21, 1946.

The Second Incident

The war had been over for some time now, but the U.S. was on the brink of the Cold War and needed to further its nuclear knowledge. Louis Slotin, a Canadian physicist who had worked on the Manhattan Project, had become one of the lead researchers working with the demon core. He was notably confident; after all, when it came to handling dangerous quantities of plutonium, he was the world's most knowledgeable man.

Slotin had developed a procedure of adjusting beryllium domes over the demon core to reflect neutrons and edge the core toward criticality. This procedure involved holding the dome steady with one hand and carefully adjusting the gap with the other hand using a long screwdriver. It was a low-tech procedure that Slotin's superiors had advised against.

All of a sudden, Slotin's hand slipped, and the core went supercritical. It dosed Slotin and the seven other researchers in the room with gamma radiation. As that same bright blue light filled the room, Slotin reached down to remove the half-sphere of beryllium and stop the reaction. Once again, it was too late.

In less than a second, Slotin had received a lethal dose of radiation. According to another scientist in the room, Raemer Schreiber, Slotin's words after the incident were calm. He had comforted Daghlian after the first incident, and he knew what came next.

"Well, that does it," he said.

He died nine days later.

Luckily for the others in the room, Slotin's body shielded them from lethal doses of radiation, and no one received any lasting injuries. It was at this point that the core became known as the demon core.

Los Alamos soon made radical changes to their testing procedures, requiring all criticality experiments to be completed remotely. The demon core had begun emitting higher doses of radiation as a result of these incidents and was subsequently melted down to be recast for other cores.

Strangely, both of these horrific events took place on a Tuesday, and both on the 21st day of the month. The two physicists were even said to have passed away in the exact same hospital room. The bizarre, eerie, and even creepy story of the nuclear demon core brings us back to a time when scientific research was done without concern for safety. These two men died working on world-changing research at a time when governments were in a global arms race.

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For more on the early days of nuclear weapons, check out "The Making of the Atomic Bomb," the Pulitzer Prize-winning book by Richard Rhodes. We handpick reading recommendations we think you may like. If you choose to make a purchase, Curiosity will get a share of the sale.

Written by Trevor English July 13, 2018

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