In September 1943, mathematician John von Neumann had proposed a design by which a fissile core could be surrounded by two totally different excessive explosives that produced shock waves of different speeds. Alternating the faster- and slower-burning explosives in a fastidiously calculated configuration would produce a compressive wave upon their simultaneous detonation. This so-called “explosive lens” focused the shock waves inward with sufficient force to rapidly compress the plutonium core to a quantity of instances its original density. This lowered the size of a important mass, making it supercritical. It additionally activated a small neutron supply at the heart of…
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