Plutonium

[Stav]

How much Plutonium or Uranium is needed to make a weapon 'nuclear'? Why is it called weapons grade plutonium, or uranium?

[Hamish]

Why do you want to know this?!

[rekstout]

5kg Plutonium or 15Kg Uranium or thereabouts is the normal amount required to form a critical mass for an uncontrolled nuclear fission reaction.

It is not simply a case of a certain mass of fissile material being required but the more configuration of that material (shape) - one can have a single mass of fissile material greater than that without it "going off", provided it is of a certain shape or density.

So-called "weapons grade" materials are of a greater purity as less pure materials are contaminated with - for example - undesirable isotopes which will absorb or block the flow of neutrons required to sustain a chain reaction. The stuff you get in nuclear power plants is usually of insufficient purity to manufacture a fission weapon but suitable for the "dirty bombs" we hear so much about at the moment. - I'm not a scientist so I hope I got that right - Our esteemed colleague from Imperial should be able to provide a more comprehensive answer.

[incitatus]

The weights given equate to a lump about the size of a grapefruit. In order to get it to go off you need to bring the lumps together with great precision, the best bet is a spherical implosion wave.....All this is public record stuff, by the way. nothing you cant fiind in a textbook. Plutonium is much more easy to use as a weapon than uranium...with uranium you need to purify the isotopes, which is tricky, but all plutooinum is essentialy weapons grade.... If you want a dirty bomb anything will do, it just has to be spread over a wide area. The shape of the fissile lump is important, as you need the statistical likelihood that each fission will ignite two others. This is dependant on the barn ratios of the elements invovled as well as the denity of the material, but generally a sphere is best. But I strongly advise you not to try it. Honestly all this stuff is in standard texts...but in terms of practical details it is very hard indeed to put together a bomb even when you know how it works. It took the yanks and us years. take up knitting instead