### Possible Answer

The Bethe-Feynman efficiency formula, a simple method for calculating the yield of a fission bomb, [1] was first derived in 1943 after development in 1942. - read more

Feynman and the Bomb by Alex Wellerstein, ... Developing formulae relating to criticality and implosion efficiency (including the Bethe-Feynman formula) - read more

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