Nuclear handgrenades

So, what's the definition of a nuclear weapon? I suppose most people, dredging up memories from high school think it involves Plutonium or Uranium as part of a Fussion or Fission device? Maybe a few people would throw in dirty bombs designed to throw around radioactive particles? I would imagine that everyone has a *BIG* explosion in mind?

Currently, there is a ~10 year old Federal law prohibiting the U.S. from developing nuclear weapons that yeild less than 5 kilotons of power, but there have been a number of nuclear weapons tested much smaller than the 5 kiloton cutoff. I tend to like the development ban, being that if a nuclear weapon needs to be used, there's not a whole lot of point in using a small one. If there isn't moral and legal grounds to use a nuclear bomb, it doesn't pay to be tempted to argue that a small one is equivalent to just using a couple extremely large conventional bombs.

Anyway, at some point there's a cutoff at how small an efficient nuclear bomb can be and still reliably detonate. (That's the business about "critical mass" that most of us slept through in HS).

However, there's a possible endrun around the legal and scientific limitations in making small nuclear bombs: hafnium explosives. Greatly simplified, halfnium can *probably* be charged up with energy, on the order of 50 kilograms of TNT per gram, and can be used in any amount, large or small. Detonated, it does throw off gamma rays and some radioactive particles. Is it a nuclear weapon? I have no idea. If, and that's a big if, the whole charged isotope thing gets sucessfully developed, there's an interesting potential for the world's best batteries.