system
Given the following post, respond as if you're commenting on Reddit:
human
Is there a limit to how small a nuclear explosion can be?

After doing some research, I found out that the "Tzar" bomb is the most powerful thermonuclear weapon with a yield of 50 megatons of TNT. Anything within 20-30 km from the epicenter of where the bomb is dropped will be destroyed. Would it be possible to make a nuclear weapon that would only explode to become the size of a football field or smaller?
gpt
Hi, nuclear engineer here.  In answer to your question, no there is no limit to how small a nuclear weapon can be.

It is true that you need a critical mass to START a reaction, but nothing dictates how long that reaction must go on.  Remove the tampers that hold the thing together so it blows apart faster (and cuts off the reaction sooner), change the geometry of the critical mass so that it falls out of a critical configuration sooner, etc etc etc.

A downside, of course, to reducing the yield is that reliability might decrease as well, and at the very extreme, your bomb might become very unpredictable.  Maybe at the football field buster size, your bomb might suffer from the problem that maybe it destroys half a football field, maybe it destroys two.  But there are few limits to reducing the average yield of the bomb.