What was the Demon Core?

Update (7/23/2023): Lots of people are asking what would have happened to the core if the beryllium shields were left on the core during the second experiment. The core would NOT have detonated like in the Hiroshima and Nagasaki bombings. Instead the core would have heated up to the point of melting, likely burning the lab down, and simultaneously emitting tons of radiation. Then as the core melted and lost its shape, it would have gone subcritical as it would have had less surface area to absorb the reflected particles. Infographic posters here: Support QFS: Twitter: Facebook: Check out my history channel: Check out my other videos! What Happens When You Drink Bleach? Science of the Gallows