The Demon Core: The Plutonium Sphere That Killed Twice

Physicists are not superstitious people. They deal in measurement, not omens. So when a group of them started calling a particular lump of plutonium the "demon core," it was worth paying attention, because the thing had, in less than a year, killed two of their colleagues in almost the same way, in the same room, by the same careless instant. The core did nothing supernatural. It simply sat there being lethal, and twice a brilliant man got too close and paid for it within days.

The demon core is a true story from the dawn of the atomic age, and it needs no folklore to chill you.

A sphere with a job

The core was a subcritical sphere of plutonium, about the size of a grapefruit, manufactured at Los Alamos in 1945 as a ready weapon core for a third atomic bomb, intended for use against Japan if the war continued. Japan surrendered before it was needed, so the core stayed in the laboratory, where scientists used it for criticality experiments, dangerous tests that nudged fissile material toward the edge of a chain reaction to study its behavior. The work involved bringing neutron-reflecting materials close to the core, which bounced neutrons back in and pushed it toward "going critical." Get it right and you learned something. Get it wrong and the core released a burst of radiation.

Twice, someone got it wrong.

The two who died

In August 1945, the physicist Harry Daghlian was working alone at night, stacking tungsten-carbide bricks around the core to reflect neutrons. He fumbled and dropped a brick directly onto the assembly. The core went briefly supercritical, released a flash of radiation, and Daghlian, though he pulled the brick away fast, absorbed a fatal dose. He died about a month later.

Less than a year on, in May 1946, the physicist Louis Slotin performed an even more reckless version of a related experiment, holding two neutron-reflecting half-spheres apart around the core with the blade of a screwdriver, a technique colleagues called "tickling the dragon's tail." The screwdriver slipped. The halves closed, the core flashed blue, and Slotin, who yanked the pieces apart with his bare hand and likely saved the seven others in the room, died in agony nine days later. Same core, same fatal instant of contact, a second time.

It is worth being plain that there is nothing paranormal here. The "demon" was physics and human error, a material so unforgiving that a dropped brick or a slipped screwdriver was a death sentence. But you can see why the survivors reached for the language of the cursed.

The residue of a named object

The science is complete and grim: criticality, neutron reflection, acute radiation syndrome. What lingers is the pattern, one object, two men, two nearly identical mistakes, two deaths within days, and the fact that the physicists themselves gave it a name usually reserved for haunted things. The core was later melted down and recycled into other weapons, the "demon" dissolved into the stockpile. Rationally it is a warning about handling. The residue, the eerie symmetry of the two deaths, does not tidy away, and that is what our readers argue over.

Below, readers have filed their own encounters with objects that seem to bring harm to those who handle them, each voted True, Fake or Not sure by the jury. Read them and cast your verdict.