What stops a nuclear bomb’s chain reaction?

Question

What stops a nuclear bomb’s chain reaction?

In: 9

Answer 1

After it has begun? The core undergoes a prompt-critical chain reaction which either fissions all of the available fuel, or which stops when the resultant explosion blows apart the core, preventing fission neutrons from colliding with fissionable nuclei and halting the chain reaction. This is why some weapons have lead or depleted uranium tampers surrounding the core, in an effort to increase fission yield (% of core mass consumed by the chain reaction) by keeping it contained even a few microseconds longer.