Chuck's discussion of uranium enrichment technology is very interesting.  I just have a comment to add to the discussion, about bomb technology. One reason a uranium bomb is attractive relative to a plutonium bomb is that the things are pretty much foolproof to build.  (That's why there was no test of the "Little Boy" uranium bomb dropped on Hiroshima -- or, more properly, that's why the Hiroshima drop *was* the test.)  Uranium bombs can work with a "gun and bullet" assembly, where you achieve critical mass by shooting two subcritical pieces of uranium together.  Plutonium fissions much more quickly, and if you try a "gun and bullet" assembly of subcritical plutonium pieces, the weapon will fizzle.  As a result, plutonium bombs have to achieve criticality by implosion, and that requires the design of complex shaping charges and precise timing of the explosion.  It's trickier, and a lot easier to get wrong, so it's easy to understand why would-be nuclear powers might prefer to try building a bomb out of uranium.  (After all, the resource-intensive enrichment process is just a startup cost...) By the way, I think the media/government discussion of how many "years" a country is away from having a bomb (or in the case of Iran, I've heard "weeks"(!!!)) is pretty useless.  It's pretty clear that Iran hasn't got its technological ducks in a row *right now*, and there's considerable internal opposition to the idea anyway.  (When a Grand Ayatollah issues a fatwa against acquiring nuclear weapons, to say the idea is "controversial" is an understatement.)  And, although it's nice to have the facts in hand, they're really only useful for convincing "moderate" wafflers to take our side of the issue -- the neocons want a war with Iran, facts be damned.  What we need there is some sort of propaganda offensive to defeat them -- which the Dems have shown themselves to be incompetent at. Sorry, just thinking about this stuff depresses me. -- John S Costello <a href="mailto:joxn.costello@gmail.com">joxn.costello@gmail.com</a> "[O]nce the running of the state involves a permanent and massive shortage of historical knowledge, that state can no longer be run strategically." -- Guy Debord