Purely coincidentally, the latest film I've posted for my "Sixty Symbols" series of films about physics deals with the first nuclear test...

 

 

Was intrigued to compare the two.. particularly that the North Korea test is believed to be 20KT, same as Trinity!!!?

 

Or is that not a coincidence?

Maybe this is a convenient size for an atomic bomb? To get smaller or larger requires additional work and technology.

~20kt is what you get when you can scrape together just enough to make a simple bomb. with more technological wizardry you can reduce the yield(and use less fissionables) but this is far more complex than making a more powerful bomb. so no surprises there.

 

what would be surprising would be if it were more than 100kt.