Explain the key difference in design between a gun-type and an implosion-type fission weapon.

The key difference between gun-type and implosion-type fission weapons lies in how they achieve a supercritical mass of fissile material, the amount of material needed to sustain a rapidly escalating nuclear chain reaction. A gun-type weapon, like the 'Little Boy' bomb dropped on Hiroshima, uses a relatively simple method. It consists of two subcritical masses of fissile material (typically Highly Enriched Uranium). One mass is shaped like a cylinder and is 'fire....