Almost everyone knows about the atomic bomb explosions that the United States inflicted on Japan at Hiroshima and Nagasaki, but fewer people know that there was a third bomb in the works.
Japan surrendered so it was never used, but America had a third atomic bomb nearly ready, with a core of refined plutonium and gallium.
When the plan shifted, the core was used in detonation research, and became part of a very creepy series of events.
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It was repeatedly involved in horrific research accidents, earning the name 'demon core'.
Scientists wanted to use it to work out exactly where the tipping point was for changing these cores into explosive nuclear chain reactions - something known as going 'supercritical'.
This basically involved prodding the core (with much more sophisticated methods) to see how it would react, and in 1945 this caused the first accident.
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A scientist called Harry Daghlian was working alone with the core, a breach of protocols, when he accidentally dropped a tungsten carbide brick on it, causing it to go supercritical. When he reached in to retrieve the brick, he was instantly given a fatal dose of radiation - and less than a month later, he died of radiation poisoning.
It was a horrific incident, but didn't stop teams from testing the core, and in May 1946 another accident occured.
This time scientists were putting two beryllium dome half spheres around the plutonium core - and when the two halves were accidentally allowed to touch, it caused a reaction that made the core go supercritical and blast radiation out into the room around it.
Every scientist in the room got a dangerous dose of radiation, and one, Louis Slotin, was killed by his proximity to the core.
These horrific accidents forced the scientific teams and institutes to urgently update their safety protocols.
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Amazingly, given they knew at least some of the effects of radiation, scientists hadn't been bothering with protective clothing or shielding, something that now is almost incomprehensible.
This was soon to change, but the 'demon core' wasn't around to see it happen - in response to these terrible incidents, it was melted down to form smaller cores for other bombs and missiles in the US nuclear arsenal.
That's still a pretty depressing end to an already scary story, though, and underlines that the experiments that led to some of those terrifying bombs were themselves quite frightening to live through, even if they paled in comparison to the suffering the bombs would cause directly.
Featured Image Credit: Los Alamos National Laboratory