It was August 13, 1945, and the “demonic core” was ready, waiting to be unleashed upon a stunned Japan still reeling from the deadliest attacks yet to be seen.
A week earlier, “Little Boy” exploded over Hiroshima, followed quickly by “Fat Man” in Nagasaki.
They were the first and only nuclear bombs ever used in the war, claiming up to 200,000 lives – and if things had turned out a little differently, a deadly third strike would have followed in their hellish wake.
But the story had other plans.
After Nagasaki proved that Hiroshima was no fluke, Japan quickly surrendered on August 15, with Japanese radio broadcasting a recorded speech of Emperor Hirohito conceding to Allied demands.
It turns out it was the first time the Japanese general public had heard the voice of one of their emperors, but for scientists at the Los Alamos Laboratory in New Mexico – aka Project Y – the event had a more urgent meaning.
This meant that the functional core of the third atomic bomb they were working on – a 6.2 kilogram (13.7 pound) sphere of refined plutonium and gallium – would ultimately not be needed for the war effort.
Had the conflict still raged, as it had for nearly five consecutive years, this plutonium core would have been embedded in a second Fat Man construct and exploded over another unsuspecting Japanese city four days later. later.
As it stands, fate granted those souls a reprieve, and the Los Alamos device — codenamed “Rufus” at this point — would be kept at the facility for further testing.
It was during these tests that the remaining nuclear weapon, which eventually became known as the Demonic Core, gained that name.
The first crash occurred less than a week after Japan’s surrender, and only two days after the date of the canceled Demonic Core bombing.
This mission may never have been launched, but the demon core, stranded in Los Alamos, still found an opportunity to kill.
Los Alamos scientists knew well the risks of what they were doing when they conducted criticality experiments with it – a way to measure the threshold at which plutonium would become supercritical, the point where a nuclear chain reaction would trigger an explosion. deadly radiation.
The trick performed by the Manhattan Project scientists – of which the Los Alamos lab was a part – was to find how far you could go before this dangerous reaction kicked in.
They even had an informal nickname for high-risk experiments, which alluded to the dangers of what they were doing. They called it “tickling the dragon’s tail”, knowing that if they had the misfortune to wake the angry beast, they would be burned.
And that’s exactly what happened to Los Alamos physicist Harry Daghlian.
On the night of August 21, 1945, Daghlian returned to the lab after dinner, to tickle the dragon’s tail alone – with no other scientist (just a security guard) around, which was a violation of security protocols.
As Daghlian worked, he surrounded the plutonium sphere with tungsten carbide bricks, which reflected neutrons emitted from the core back to it, bringing it closer to criticality.
Brick by brick, Daghlian built these reflective walls around the core, until his neutron monitoring equipment indicated that the plutonium was about to go supercritical if he placed any more.
He moved to remove one of the bricks, but in doing so accidentally dropped it directly on top of the sphere, inducing supercriticality and generating a glow of blue light and a heat wave.
Daghlian immediately reached out and removed the brick, noticing a tingling sensation in his hand.
Unfortunately, it was already too late.
In that brief moment, he had received a lethal dose of radiation. His burned and irradiated hand blistered and he eventually fell into a coma after weeks of nausea and pain.
He was dead just 25 days after the accident. The on-duty security guard also received a non-lethal dose of radiation.
But the core of the demon was not finished yet.
Despite a review of safety procedures after Daghlian’s death, the changes made were not enough to prevent a similar accident from occurring the following year.
On May 21, 1946, one of Daghlian’s colleagues, physicist Louis Slotin, was demonstrating a similar criticality experiment, lowering a beryllium dome onto the nucleus.
Like the tungsten carbide bricks before it, the beryllium dome reflected neutrons back to the core, pushing it toward criticality. Slotin took care to ensure that the dome – called sabotage – never completely covered the core, using a screwdriver to maintain a small gap, acting as a crucial valve to allow enough neutrons to escape.
The method worked, until it no longer did.
The screwdriver slipped and the dome fell, for a moment completely covering the demon’s core in a bubble of beryllium bouncing too many neutrons back at it.
Another scientist in the room, Raemer Schreiber, turned at the sound of the dome falling, feeling the heat and seeing a blue flash as the demon’s core went supercritical for the second time in the space of a year.
“The blue flash was clearly visible in the room although it (the room) was well lit by windows and possibly ceiling lights,” Schreiber later wrote in a report.
“The total duration of the flash could not have been more than a few tenths of a second. Slotin reacted very quickly by turning the burglar-proof piece over.”
Slotin may have been quick to rectify his fatal mistake, but again the damage was already done.
He and seven other people in the room – including a photographer and a security guard – were all exposed to a burst of radiation, although Slotin was the only one to receive a fatal dose, and a higher dose than that inflicted on Daghlian .
After an initial episode of nausea and vomiting, he initially appeared to recover in hospital, but within days he was losing weight, experiencing abdominal pain and beginning to show signs of mental confusion.
A press release issued by Los Alamos at the time described his condition as “three-dimensional sunburn.”
Nine days after the screwdriver slipped, it was gone.
The two fatal crashes, just months apart, finally saw real change happen at Los Alamos.
New protocols meant the end of “hands-on” criticality experiments, with scientists forced to use remote-control machines to manipulate radioactive nuclei from a distance of hundreds of meters.
They also stopped calling the plutonium core “Rufus”. From then on it was only known as the “Demon Core”.
But after all that had happened, the time of the remaining nuke was also up.
Following the Slotin accident – and the resulting increase in core radiation levels – plans to use it in Operation Crossroads, the first post-war nuclear explosion demonstrations to start on Bikini Atoll a month later, were discontinued.
Instead, the plutonium was melted down and returned to the US nuclear stockpile, to be remelted into other nuclei as needed. For the second and final time, the Demon Core was denied its detonation.
While the deaths of two scientists can’t compare to the untold horrors if the demon’s core had been used in a third nuclear attack on Japan, it’s also easy to see why the scientists gave it the superstitious name they gave it. do.
Then there are the odd details that fill the story’s backdrop.
Like how Daghlian and Slotin weren’t just killed by similar accidents involving the same plutonium core: both incidents took place on Tuesday, the 21st, and the men even died in the same hospital room. .
Of course, these are just coincidences. The core of the demon wasn’t really demonic. If there’s any evil presence here, it’s not the core, but the fact that humans rushed to make these terrible weapons in the first place.
And the real horror – besides the horrific effects of radiation poisoning – is the spectacular way in which scientists in the mid-20th century failed to protect themselves from the extreme dangers they were playing with, when they knew fully aware of the serious risks that surrounded them.
According to Schreiber, Slotin’s first words immediately after the screwdriver incident were simple and already resigned.
He had comforted his dying friend Daghlian in the hospital, and he knew what was coming next.
“Well,” he said, “that’s enough.”
A version of this article was first published in 2018.