The Demon Core: History's Most Dangerous Sphere, Made Safe for Your Desk

It was only about 3.5 inches across, roughly the size of a grapefruit, and it weighed around 13 pounds. It was a sphere of plutonium built for the Manhattan Project, and in less than a year it killed two of the scientists who handled it. Afterward, people called it the Demon Core.

Two accidents, one sphere

On August 21, 1945, physicist Harry Daghlian was working alone at Los Alamos, stacking tungsten carbide bricks around the core to reflect neutrons back into it. One brick slipped from his hand and landed on the sphere. The core briefly went critical. He knocked the brick away, but he had already received a fatal dose of radiation and died weeks later.

Nine months later, on May 21, 1946, Louis Slotin was demonstrating a procedure his colleagues called "tickling the dragon's tail." He lowered a hollow beryllium hemisphere over the core while holding the gap open with the tip of a screwdriver. The screwdriver slipped. A blue flash filled the room, and Slotin flipped the shell off with his hand. His quick move probably saved the others in the room, but he died nine days later.

The core was meant for a third bomb that was never used. It was later melted down and its plutonium was reused.

Our replica (no radiation included)

We print our Demon Core in silver silk PLA, a plastic with a sheen that reads almost like chrome. The inner sphere stands in for the plutonium core. The outer shell represents the beryllium reflector, and the core nests snugly inside it and lifts right out. At 3.5 inches across, it matches the size of the original. It ships with a small stand so it won't roll off your desk.

People buy it for very different reasons:

• Fidgeting: pulling the core out of the shell and snapping it back is oddly satisfying
• Teaching: history and physics teachers use it as a classroom prop
• Collecting: it's a strange, true story you can hold in one hand
• Gifting: it's a strong pick for the dad, nerd or history buff who has everything

Items arrived perfectly. Great gifts for anyone who loves unique gifts. A+ item.

Bonnie, Etsy review of our Demon Core

Want it in color? Meet the Orb

The same sphere-in-a-shell also comes in bright colors as our Orb, sometimes all one color right down to the stand. Tell us your favorite colors when you order, or let us surprise you.

Go big: the 6-inch Demon Core

For classrooms and lecture halls, there's also a large 6-inch version, almost double the size of the original, made for a professor's desk or a science-class display shelf.

More strange and wonderful prints are in our 3D printed guide, and gift ideas are in our gifts for dad guide.