No, not 60 pounds.
If you don't have enough fissionable material for a supercritical mass, then you get no "boom." A mere "critical mass" won't explode (just radiate). So unlike most things in life, nuclear physics can't just scale down atomic explosions by using less fisionable material...below a certain point (although smaller explosions can be made with larger amounts of fissionable material, if desired).
Uranium is a very fissionable isotope. Unlike Plutonium, Uranium can be used in gun-type atomic bombs. The American Richard Feynman was responsible for correctly calculating the amount of uranium needed to achieve critical mass (his enemy opponent in Germany, Heisenberg, got this math wrong - destroying Nazi efforts to build their Bomb). Critical mass is the amount of uranium needed to start a *self-sustaining* chain reaction. However, if you have a certain amount more than the required mass to start the reaction, a supercritical mass, the reaction would take place faster and grow exponentially (i.e. "explode"). Feynman calculated about 50 kilograms (110 lb.) of pure Uranium would be required. However, the Uranium obtained was seldom pure, so a larger amount would be needed. Robert Oppenheimer said that the required supercritical mass would be about 100 kilograms (220 lb.) of available, highly processed Uranium.
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Name: Little Boy Type: Uranium gun-type fission Weight: 9,700lb (4400 kg) Length: 10 ft, 6 in (3.2m) Diameter: 29 in (0.737m) Explosive Yield: 15,000 tons of TNT |