Curiosa: They originally determined the critical mass of plutonium by hand, with only a thin coating on the plutonium metal to prevent chemical toxicity. The experiment is affectionally called 'tickling the dragon's tail', a term coined by Richard Feynman.
The idea was to stack enough plutonium by hand in a desired configuration(e.g. two plutonium half-spheres and some bricks of graphite) until you were very close to criticality. At least two people died from accidentally reaching critical mass and recieving a massive dose of x-ray and gamma radiation.
The idea was to stack enough plutonium by hand in a desired configuration(e.g. two plutonium half-spheres and some bricks of graphite) until you were very close to criticality. At least two people died from accidentally reaching critical mass and recieving a massive dose of x-ray and gamma radiation.