Eli5: When a nuclear explosion happens and neutrons hit a nucleus and an explosion happens, knowing that Nuclear chain reaction exists, why does the explosion end at some point ?

Question

Eli5: When a nuclear explosion happens and neutrons hit a nucleus and an explosion happens, knowing that Nuclear chain reaction exists, why does the explosion end at some point ?

In: 1

Answer 1

Neutrons only trigger more decay when they hit the right kinds of atoms at the right speed. This is reasonably likely when you have a dense clump of enriched uranium. Once that clump starts exploding, it gets way less dense. Neutrons created then miss the other fissile atoms and just fly off, failing to continue the reaction