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The demon core was a sphere of plutonium–gallium alloy that was involved in two fatal radiation accidents when scientists tested it as a fissile core of an early atomic bomb.

It was manufactured in 1945 by the Manhattan Project, the U.S. nuclear weapon development effort during World War II. The core was prepared for shipment to the Pacific Theater as part of the third nuclear weapon intended to be dropped on Japan, but when Japan surrendered, the core was retained for testing and potential later use in the case of another conflict. The two criticality accidents occurred at the Los Alamos Laboratory in New Mexico on August 21, 1945, and May 21, 1946. In both cases, an experiment was intended to demonstrate how close the core was to criticality, using a neutron-reflective tamper (layer of dense material surrounding the fissile material). In both accidents, the core was accidentally put into a critical configuration. Physicists Harry Daghlian (in the first accident) and Louis Slotin (in the second accident) both suffered acute radiation syndrome and died shortly afterward. The core was melted down during the summer of 1946, and the material was recycled for use in other cores.

The demon core was a solid 6.2-kilogram (14 lb) softball-sized sphere measuring 89 millimeters (3.5 in) in diameter; it was similar to the core used in the bombing of Nagasaki. The core of the device used in the Trinity Test at the Alamogordo Bombing and Gunnery Range in July did not have such a ring. Material for "HS-7, R-3" was in the Los Alamos metallurgy section and would also be ready by September 5 (it is not certain whether this date allowed for the unmentioned "HS-8"'s fabrication to complete the fourth core).

These factors are not common in the environment; they are only likely to occur under conditions such as the compression of the solid metallic core (which would eventually be the method used to explode the bomb), the addition of more nuclear material, or provision of an external reflector which would reflect outbound neutrons back into the core. While attempting to stack another brick around the assembly, Daghlian accidentally dropped it onto the core and thereby caused the core to go well into supercriticality, a self-sustaining critical chain reaction.

On May 21, 1946, physicist Louis Slotin and seven other personnel were in a Los Alamos laboratory conducting another experiment to verify the closeness of the core to criticality by the positioning of neutron reflectors. It required the operator to place two half-spherical shells of beryllium (a neutron reflector) around the core to be tested and manually lower the top reflector over the core using a thumb hole at the polar point.

After these incidents, the core, originally known as "Rufus", was referred to as the "demon core".

The demon core was intended for use in the Operation Crossroads nuclear tests, but after the second criticality accident, time was needed for its radioactivity to decrease and for it to be re-evaluated for the effects of the fission products it held, some of which were very neutron poisonous to the desired level of fission. The next two cores were shipped for use in Able and Baker, and the demon core was scheduled to be shipped later for the third test of the series, provisionally named Charlie, but that test was canceled because of the unexpected level of radioactivity resulting from the underwater Baker test and the inability to decontaminate the target warships.

The "demon core" is often portrayed in popular culture as an example of a scientific cautionary tale. In 2023, the post-punk band Unborn Ghost released a song titled "The Worm at The Demon Core", alluding to the "demon core" and William James' phrase "the worm at the core", from The Varieties of Religious Experience.

Quick Facts

• In 2023, the post-punk band Unborn Ghost released a song titled "The Worm at The Demon Core", alluding to the "demon core" and William James' phrase "the worm at the core", from The Varieties of Religious Experience.
• In both cases, an experiment was intended to demonstrate how close the core was to criticality, using a neutron-reflective tamper (layer of dense material surrounding the fissile material).
• The demon core was a solid 6.2-kilogram (14 lb) softball-sized sphere measuring 89 millimeters (3.5 in) in diameter; it was similar to the core used in the bombing of Nagasaki.
• The two criticality accidents occurred at the Los Alamos Laboratory in New Mexico on August 21, 1945, and May 21, 1946.
• In both accidents, the core was accidentally put into a critical configuration.

Source material: Wikipedia - "Demon core". Adapted and summarized for DiscoverScroll. Original contributors are credited through the linked Wikipedia article. Read original on Wikipedia. CC BY-SA 4.0. Changes were made from the original.