3D Printed Demon Core Lamp

Hey Makers! Jarrid again, with a Takeover project I thought my fellow science enthusiasts would enjoy. This is a small tribute to the brave men and women who risked their lives studying the effects and uses for radioactive materials in the early criticality experiments of the 1940s. The 3D Printed Demon core is based on the spherical plutonium core, called Rufus, which became known as the Demon core after the incidents on August 21, 1945, and May 21, 1946.


With nuclear power being a talking point of late due to carbon emission concerns and the heavy water in Fukushima, I thought it would be a good idea to honor the pioneers of the field. while also showing how far we have come in this incredible technology. This was a pretty simple print, but what it represents is far more intricate. To better understand how fission and fusion worked, scientists tried to induce criticality of the core of a nuclear bomb, without the devastating explosion.

Sadly at the time, we did not understand the extent of radioactive damage so very few safety measures were implemented. This, unfortunately, cost the lives of two Scientists studying the core. However, there were positives to all this, while the core was melted down, its lessons lead us to where we are today. While nuclear power is still daunting to a lot of people, the risks are significantly lower. It now takes 2 natural disasters to cause a meltdown(Fukushima) instead of human error which is a lot more common.

What was the Demon Core?

The spherical plutonium core, called Rufus, was created during World War II as part of the United States nuclear weapons development effort. Rufus was intended to be used as a third nuclear weapon to be dropped on Japan. The end of World War II put a stop to this and the core was sent to the Los Alamos Laboratory for testing. During criticality experiments, there were two accidents, one in 1945 and one in 1946, and both caused Rufus to become supercritical.

The Incidents

On August 21, 1945, Harry Daghlian Jr. was performing a neutron reflector experiment. He was placing neutron-reflective tungsten carbide bricks around the core when he accidentally dropped one onto the core causing it to go supercritical. He quickly removed the brick but had already received a fatal dose of radiation. Sadly, 25 days later, he passed away from acute radiation poisoning.

On May 21, 1946, physicist Louis Slotin and other personnel were conducting another neutron reflector experiment. It required the operator to manually place two half-spheres of beryllium (the neutron reflector) around the core using a thumb hole on the top. The spheres were never to completely enclosure the core as it would cause it to go supercritical, so a screwdriver was placed between the half-spheres to prevent this. During the experiment, the screwdriver slipped and the spheres covered the core causing it to go supercritical. Slotin quickly flipped the top half off the core which ended criticality in seconds. Sadly he had already received a fatal dose of radiation and passed away 9 days later from acute radiation poisoning.

These incidents caused Rufus to be renamed the Demon core. So where is the Demon core now? It was melted down and the material was recycled for use in other cores. The Demon core legacy will live on through the safety regulations and other changes made as a result of the incidents.

You can find out more on the Wikipedia page.


This projects makes use of both 3D Printed and electronic components. I have linked the products I used if you wish to make your own Demon Core Lamp.

The 3D Printer files required can be found here:
Demon Core lamp by Bergi X


I followed the instructions provided by Bergi X for the 3D Printed Demon core

  1. You should be able to print the upper and lower reflector easily without any supports. Use a nice contrasting color to print the spacer blocks.
  2. There are two versions of the core. If you have transparent or translucent PETG, use the 0.5 mm version. If you only have access to colored PLA, print the core as thin as you can. Never mind that the top of the core might turn out a little perforated, the upper reflector can hide this part of the core.
  3. The lower reflector has enough room for electrical wiring. I suggest you use some cheap USB-powered fairy lights. Use low-power light sources and be careful not to melt or burn the material! Finally, use the spacer blocks to prop up the upper reflector as precariously as you dare.

Final Thoughts

If I could change anything about this design I would add the names of the scientists on the base. Other than that the story of this infamous device does all it needs to as a cautionary reminder of the sleeping dragon that is nuclear power.

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