“Gentleman, what we have here is the most powerful force ever created by mankind. Lets poke at it with a screwdriver.” —Louis Slotin, Los Alamos Laboratory

After World War II the scientists at Los Alamos laboratory found themselves in possession of a spare core originally intended for a nuclear bomb. Nicknamed “Rufus” the core would have been detonated as part of a third nuclear bomb dropped on Japan, however the Japanese surrendered before the bomb could be assembled. Instead the 89mm (3.5 inch) diameter sphere of plutonium-gallium was reserved for scientific testing, in particular criticality experiments.


Critical mass is the minimum amount of mass needed for a fissile material to sustain a nuclear chain reaction. When a fissile material reaches critical mass, it becomes “supercritical”, where it releases a large amount of energy.  Rufus was 5% subcritical, thus scientists thought it was ideal for use in criticality experiments. The experiment was designed to simulate critical mass by surrounding the core with neutron reflectors, in this case tungsten carbide bricks. The bricks would deflect released neutrons back into the core, increasing its reactivity. Completely surrounding the core would cause it to go supercritical, an event which was to be avoided because it would release a burst of neutron radiation that could kill everyone in the room. Essentially the purpose of the experiment was to see how much nuclear material could be added to the core before it would go supercritical, and measure how much energy is released in the process.

On August 21st, 1945 physicist Harry K. Daghlian Jr., was conducting a criticality experiment with Rufus when he accidentally dropped a tungsten carbide brick on the core. The core went supercritical, releasing a burst of neutron and gamma radiation while bathing the room in a bright blue light. Daghlian promptly responded by removing the brick from core, causing his hand to instantly blister from the radiation.

Daghlian had received a deadly dose of radiation, resulting in his death 25 days later. An accompanying guard,  Army Private Robert J. Hemmerly, was sitting at a desk 12 feet away but seemed unharmed by the accident, although he died 33 years later from leukemia.

Louis Slotin

After the accident, Rufus was renamed, “The Demon Core”. A new procedure was designed to make the experiment “safer”, which was designed by physicist Louis Slotin. The new procedure involved the core sitting between two beryllium half spheres. A screwdriver was jammed in between the two half spheres, creating a gap through which neutrons could escape. The screwdriver was used to manipulate the half spheres, raising or lowering them to increase or decrease the size of the gap, thus increasing or decreasing the reactivity of the core. If the two half spheres completely enclosed the core, it would go supercritical.

If this sounds completely insane, you probably have more common sense than the brilliant physicists who conducted these experiments. In fact the experiment was named “Tickling the Dragon’s Tail”, based on a remark by physicist Richard Feynman who compared the experiment to “tickling a sleeping dragon”. Slotin was certainly aware of the dangerous nature of the experiment, he had been at Daghlian’s bedside when he had died. The famed physicist Enrico Fermi had warned Slotin that if he continued these criticality experiments, he would be dead within a year.

On May 26th, 1946 Slotin was conducting a criticality experiment with the demon core when he lost control of his screwdriver, causing the beryllium sphere to close. The incident is almost perfectly re-enacted in the 1989 film “Fat Man and Little Boy.”

Louis Slotin died of acute radiation poisoning nine days later. Of the other seven people in the room, two would die of cancer years later, although it is unknown whether the accident contributed to their deaths.

After these two criticality accidents new experiments were designed which used remote controlled machines and cameras. The Demon Core was melted down and recycled into other cores.


    • You’d need a lead body condom… I suspect that they knew that there wasn’t much that shielding would accomplish.

    • Marvel had predicted such cool things – Bruce Banner, pelted by gama rays turned into the Hulk. These people turned into corpses. If only it was seventy years later, they could have been president.

    • It is fascinating that, in America, exposure to radiation begats super heroes but in Japan it begat Godzilla. It’s all perspective.

  1. “Hey Harry, hand me the New-Cleer adjusting device, says Craftsman on the side.”

    Play stupid games with the sun, get burned. PhD does not necessarily mean smart.

    According to Dr. ‘mengele” Fauci, if these guys were wearing TWO masks they would have been protected. He’s in the same league of stupid…maybe he needs a set of screwdrivers.

    • Or one of those plastic face shields – in lieu of a mask, might have saved them from the effects of the nuclear warhead.

    • I started thinking of Fauci as a boob who gives out false information, so of course my mind tagged him as Dr. Falsie…

      • …and he’s now the highest paid Federal employee. Only the worst get kicked upstairs and a pay raise, and certainly his Cayman Island account gets filled regularly. He’s a political operative who’s been massively wrong on everything he’s touched in 40 years of “service” to the little people. Yet here he is…telling people to now wear two masks. (I’ll be observing when out and about to see who’s following that imbecilic suggestion.)

          • If you whack you schwanz off, shave your legs, walk like a duck, put on a wig and a mini-skirt, you (too) could land a highly paid government job. Small sacrifice to join ‘the movement’.

          • I’m originally from PA…real Pennsylvanians are happy he’s no longer in state, ‘course, the he’s now foisted on the entire nation to effect his deranged mentality. What people do to themselves for attention.

          • @Camperfixer, if you’re referring to the holder of the Office of the Assistant Secretary of Health Elect, I’ll bet gold dollars to dog poop that no single shot caller on the left genuinely thinks of that person as a woman. Nor is it likely that they are particularly impressed by that person’s medical acumen or leadership skills.

            The whole point of putting freaks and the mentally ill in our faces 24/7 — while making it a Hate Crime to notice that they are ill — is to humiliate us. It’s no different than the “2+2=5” of 1984.

  2. It occurs to me that persons very much like Slotin are playing the same game with American society, seeing how far they can up the pressure. And of course being surprised by the deadly response. It’s always a surprise to them. High-IQ, highly credentialed fools.

  3. Richard Feynman wrote a couple of books that let you in on his thought processes; unusual might be a good descriptor. Very rapid, easy reading and quite worthwhile. I received the impression that the man never stopped asking questions – about everything under the sun (and then some).

  4. I felt uneasy reading this post. “Go on, stick that screwdriver in the demon core.” Good thing we’re not trying to make antimatter or anything like that at CERN.

  5. If Slotin had just repositioned that empty Coke bottle, maybe it would have turned out alright. Maybe break it and use glass chips to hold the beryllium halves apart.


    Science Alert did this story a couple of years ago, and if I’d seen the Demon Core before, I’d forgotten the details. The other thing to think about is that beryllium isn’t good to be around, either, especially fine chips or dust. Machining it probably made chips much too big to inhale, but that wasn’t particularly safe, either.


    • Science Alert did a better job than I did of telling the story. However the tale is cautionary if only by metaphor.

  6. Play stupid games, no matter how intelligent you are, and win stupid prizes.

    I can just imagine it… “Here, Professor, hold my (insert drink.)”

    And, yet, still to this day, I see people look down barrels of guns, walk out into the road without looking and believe the media…

  7. Years ago I worked briefly at Lawrence Livermore Labs in Livermore Cal. I worked on the non classified side with the numerous Laser experiments as an Install/High Voltage Tech. The experiments would be powered by 5kV to 16kV voltage with that supplied by banks of large capacitors. The voltage would be supplied by large copper buss bars through out the tables covered in Lexan shields. Physicists would routinely remove the shields to reach over and tweak whatever mirror or instrument or move equipment and parts. These shields were large and cumbersome to work over and around. Bare arms and hands and sometimes faces mere fractions of inches away from deadly voltage. So close the hair on arms and heads would stand up straight. Physicists would get pissed and moan and groan when we had to work on some part of the experiment because we would shut the voltage off and ground the capacitors to remove the voltage… Yeah accidents were fun sometimes…

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