The Bethe-Feynman efficiency formula, a simple method for calculating the yield of a fission bomb, was first derived in 1943 after development in 1942. Aspects of the formula are speculated to be secret restricted data

Classified information in the United States

The United States government classification system is currently established under Executive Order 13526, the latest in a long series of executive orders on the topic. Issued by President Barack Obama in 2009, Executive Order 13526 replaced earlier executive orders on the topic and modified the...

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Related formula

• a = internal energy per gram
• b = growth rate
• c = sphere radius

A numerical coefficient would then be included to create the Bethe-Feynman formula -- increasing accuracy more than order of magnitude.