– Could you make a ball of nuclear material fission by throwing it at something hard enough?

Question

So I’ve been thinking about this for a while now, and I haven’t really been able to answer my question no matter how much I look into it, I was wondering if you guys could help.

So I was wondering, the critical mass of nuclear material is easier to achieve if the material is denser. I’m also aware that this is kinda how some nuclear bombs work, by launching a chunk of material at more material to cause the explosion. (I think?)

So in that case, what would happen if you grabbed a ball of Uranium or Einsteinium and threw it at the ground hard enough? Would it go critical? If so, how hard would you have to throw it and how big would the ball need to be?

As an optional bonus if all the aforementioned is possible, if the mass of Uranium were say, the size of a bullet, how fast would you need to fire the bullet in order to achieve criticality by kinetic impact alone?

In: 0

Answer 1

Throwing or shooting a blob of metal at the ground doesn’t increase the density in any meaningful amount. Plus it would at best only increase the density at one particular spot while decreasing it around the edges. In other words it splats like an egg. At some speed then yes you could trigger an explosion, but at the expense of blowing apart the bullet in the process. And the little bit of fuel that did compress enough would blow apart the rest of the fuel before it had a chance to explode.

The trick with some nuclear weapon designs then is to compress the metal from all directions at once using very carefully shaped plastic explosives so that the density increases evenly. Think of a baseball suddenly shrunk to a golf ball. The Nagasaki bomb for example compressed its plutonium core to double its normal density. Even so the majority of the bomb blew apart before it could undergo fission, and it was very inefficient.

The other way, the bullet or gun method which was used over Hiroshima, does not require compression. Sometimes just having enough radioactive metal in one spot is enough to set off a chain reaction . You could set off the bomb simply by slapping the two halves off a sphere together. No compression needed. It was inherently more dangerous however and because there was No explosion to compress the fuel , only about 2% of the uranium actually fizzed . The other 98% blew apart uselessly