The Demon Core

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An intriguing anecdote from the beginning of the Atomic Age:

When an atom undergoes fission, it usually splits into two smaller atoms, along with a few leftover neutrons that are emitted as waste. These waste neutrons can then hit nearby atoms and cause them to fission. When a fission-type nuclear bomb explodes, what?s actually happening is that the uranium or plutonium fuel is going supercritical. This essentially means that there are enough fissioned (split) atoms pumping out enough neutrons to keep a chain reaction going. This requires a certain mass and volume of fissile material (i.e. the material?s critical mass). One of the Manhattan Project?s core areas of research was discovering the exact controlled conditions that can take a normal, radioactive lump of uranium or plutonium and make it supercritical ? thus creating an atom bomb.

While you would think that such research into supercriticality would be carried out with the chemists and physicists safely behind half a mile of rock and lead, with long mechanical armatures manipulating the fissile material, our boys at Los Alamos were a little more? er? blazè. To discover the critical mass of the plutonium cores that would be used in the Trinity test and Fat Man bombs, Los Alamos researcher Louis Slotin devised a procedure that would later be called (by Richard Feynmann no less) ?tickling the dragon?s tail.? This technique involved Slotin ? often while wearing blue jeans and cowboy boots, apparently ? lowering a beryllium hemisphere over the plutonium core. Beryllium is a neutron deflector ? so if it?s close enough to the core it bounces enough neutrons back into the plutonium, triggering supercriticality. While Slotin lowered the beryllium hemisphere with a thumb hole in the top, all that prevented it from completely covering the core was the blade of a flathead screwdriver.

He tickled the dragon?s tail almost a dozen times before the screwdriver finally slipped ? on May 21, 1946 ? causing the plutonium core to go supercritical and emit a massive burst of neutron radiation. Slotin reported a flash of blue light and a wave of heat across his skin before he managed to flip the beryllium reflector onto the floor half a second later, stopping the chain reaction in a matter of seconds. It was too late, though: He received around 1000 rad of radiation and died nine days later of acute radiation syndrome.

http://www.extremetech.com/extreme/1876 ... an-project
http://en.wikipedia.org/wiki/Demon_core

[youtube]http://www.youtube.com/watch?v=hh89h8FxNhQ[/youtube]
From the movie "Fat Man and Little Boy" (1989)

Interesting read.

Actually, that core didn't go supercritical when Slotin ticked the dragon's tail with it, it went critical and underwent a brief state of uncontrolled chain reaction, not unlike Chernobyl or Fukushima.

A supercritical chain reaction is what happens when an atomic warhead explodes, IE, the plutonium, uranium, thorium or whatever fissile material is used fissions in a fraction of a second.

Because the 'Demon Core' underwent a state of chain reaction when Slotin had his accident, the bomb that was tested with the core had a higher yield than was expected.