ELi5: Decades ago when countries were still testing nuclear bombs sometimes the scientists incorrectly predicted how large the explosions would be. How did they accurately calculate the actual size of the explosions after the fact?

Question

As the title says

In: 6

Answer 1

E=mc^2 tells you how much energy you’ll get from a given amount of mass. However the challenge in calculating the yield of a weapon is determining the efficiency. Not all of the mass in the core is going to react before it blows itself apart. To guess the efficiency and therefore the yield, you have to estimate how long adequate pressures can be maintained based on the types of explosive lenses you use to compress the core, as well as how fast the core material is disassembling itself before it can’t maintain the chain reaction. I won’t pretend to know the nitty gritty details but they used some serious computing power by 1940s standards to make their guesses on the first weapons.