When Japan bombed Pearl Harbor, they basically presaged their own demise with the United States dropping two atomic bombs on the cities of Nagasaki and Hiroshima in 1945. The two bombs caused unimaginable devastation to the cities and caused injuries and death to tens of thousands of people, making Japan surrender unconditionally. Not many of us know that there was supposed to be a third bomb that earned the moniker “demon core” because it tended to kill anyone who did not handle it with the greatest care.

Third Bomb

The Little Boy Bomb and the Fat Man Bomb, as they were called, were designed and produced in the Manhattan Project, a research and development operation during World War II. The project was headed by the United States and supported by the United Kingdom and Canada. It was Major General Leslie Groves of the US Army Corps of Engineers who oversaw the project from 1942 to 1946, while it was nuclear physicist and Los Alamos Laboratory’s Robert Oppenheimer who designed the actual bombs.

Little Boy nuclear bomb with casing open. (US Government – Manhattan Project, Public domain, via Wikimedia Commons)

The Manhattan Project started in 1939 with 130,000 people and about 2 billion USD cost, a huge chunk of which was for building factories to produce fissile material from uranium and plutonium, which were hard to produce at that time. The research and production took place in over thirty sites across the US, United Kingdom, and Canada, so it would be unbelievable to think that the plan was to create only two atomic bombs. And it indeed was incorrect.

The Atomic bomb project consumed 25% of US defense budget in WWII and remains the most expensive weapons system ever developed in history.  In terms of man-hours and money, it was the equivalent of undertaking the 20-year Panama canal project, building it in a single year, and doing it four times

By the summer of 1945, the Manhattan Project had produced enough fuel to create three bombs and a fourth one on the way. The fuel was used for the Trinity test and the two bombs.

Dropping the Two

The United States dropped the two atomic bombs over the two Japanese cities. First was in Hiroshima on August 6, 1945. On August 9, Enola Gay was supposed to drop the second bomb on Kokura, but the cloudy skies made it impossible to see the target, so they headed over to their secondary target and bombed Nagasaki instead.

Atomic Cloud Over Nagasaki, 1945. (pingnews.com, Public domain, via Wikimedia Commons)

In the only use of nuclear weapons in armed conflict, about 129,000 to 226,000 people were killed. When Japan did not immediately surrender, the United States was ready to drop its third nuclear bomb on August 19. Japan announced its surrender just three days before.

The Demon Core

Because of Japan’s surrender, the US was left with a 6.2 kg, 9 cm wide plutonium core that should’ve been for the third bomb that they decided to use for testing.

From 1945 to 1946, the core was used for experiments, although its super slim safety margin made it supercritical. One of the experiments done on the core was partially surrounding it with neutron reflectors that reflected neutrons from the nuclear fission reaction and then back into the core. The process even increased the reaction. The surrounding neutron reflectors would cause the core to rapidly enter criticality, which would release a fatal and powerful flash of radiation.

Herbert Lehr (left) and Haroutune Krikor Daghlian, Jr. (a.k.a. Harry Daghlian) (right) loading the assembled tamper plug containing the plutonium pit and initiator into a sedan for transport from the McDonald ranch house to the shot tower. (Unknown Manhattan Project photographer, Public domain, via Wikimedia Commons)

In 1945, physicist Harry Daghlian was performing an experiment, specifically placing neutron-reflecting tungsten carbide blocks around the core to bring it closer to criticality. As he was doing that, he unintentionally dropped one of the blocks onto the core, which he quickly removed. The core entered super criticality that very moment and released a deadly amount of radiation. Daghlian suffered from radiation sickness for the next three weeks before passing away. To prevent the same thing from happening, stricter safety protocols were enforced… or so we thought.

It was Louis Slotin, Daghlian’s colleague, who took over the experiments the next year. Slotin was no question a brilliant Canadian physicist, but his disregard for safety was his greatest flaw.

His experiments were pretty much the same as what Daghlian was doing. However, the only difference was that he would decide to ignore the safety protocols and just use his trusty flathead screwdriver to keep the space between the reflectors instead of using metal spacers. He got used to his extremely dangerous technique that his colleagues called “tickling the dragon’s tail.”

Regardless of how confident and lucky he was, his luck ended on May 21, 1946, when he lowered the two neutron reflecting half-spheres around the core with his screwdriver as the spacer. The screwdriver slipped and allowed the two neutron reflectors to enclose the core completely. Just like a deja vu, the core entered super criticality, emitted a bright blue flash of light, and then released a blast of Alpha and Gamma radiation.

Slotin managed to remove the reflectors, but his body had already absorbed a lethal amount of radiation. Just like Daghlian, he suffered from radiation poisoning and died nine days later. After the two incidents, the plutonium sphere was referred to as the “demon core,” and they decided just to melt it down and recycle it into other cores.

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