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Wednesday, April 11, 2007

Flipping the "OPEN" sign

My inaugural post will be a sort of re-write of a polemic that I sent to about a hundred of my closest friends. I'm running into significant ignorance on what it takes to make a fission weapon, and the threat the "Axis of Evil" I'm writing friends to give some technical information and to cool down some of the over the top rhetoric. I'm sure many of you already know this stuff, but bear with me.


The White House noise machine is having a hard time selling their much-wanted war with Iran what with all the scandals and inability to focus the public agenda after losing the House and Senate. Now a big deal is being made out of the Iranian announcement that they have 3000 centrifuges up and running to enrich Uranium. I don't know if you follow these things, but natural uranium is a blend of naturally occurring isotopes that are the same the world over, with a couple of rare exceptions in Gabon. Normally the ratio of U238 (doorstop) to U235 (go boom!) is roughly 40:1. To run a reactor uranium must be enriched to about 35:1 and a sustainable fission reaction can be maintained. It takes about 96% U235 to make Hiroshima bombs. This is sort of like the difference between 3.2 beer and Everclear. One could make a reasonable amount of fuel for one reactor to run on a regular basis with three thousand centrifuges. You would be lucky to make one low yield A Bomb. One Bomb is a suicide note, not a defense strategy. Once you have your sub critical masses of 97% pure U235 anyone with garage sized, machine shop, and absolute faith in a deity that will forgive their sorry asses can build an A Bomb. Ten kilos would do the trick for an engineer, say fifteen for the hobbyist. The other thing you need is a length of 4" gun barrel. Enriching that much uranium to bomb grade is a massive undertaking. Pakistan is the poorest country to successfully tackle that project, and they destroyed their economy doing it. Even with the wink-wink-nudge-nudge aid the US and EU gave The Pakistanis had to eat grass and sleep in ditches to get a few bombs. Summing up: Difficult and expensive to make the fuel, easy to make the device.

The other horror show is North Korea. Now they signed a treaty with the Clinton administration not to make enriched uranium. Kim Jung Ill thought the had a end run around the treaty by making plutonium in their funky reactors. A reactor can be operated in such a way that it produces lots of plutonium. The Pu can be separated fairly cheaply and easily (compared to U235). As The Dear Leader found out, making a working bomb from plutonium is not easy. The absolute amount of Pu needed is less, in weight, than U235. Plutonium is brought to criticality by a symmetrical high explosive lens that crushes the Pu to critical mass. This action is very tricky, and easy to screw up.

The BBC website has a good overview of fission devices, and they get all the numbers right.

The real threat out there are loose old Soviet nukes that, given the current state of the world, will eventually find their way into the hands of people willing to sell them. Bush and his boys haven't been big on controlling these weapons. It just doesn't fit with the forever war hysteria that tyrants everywhere so love. There is solid support in congress for policing the old Soviet stockpile, but there is no military fun or Haliburton money in controlling existing nukes.


We must have a working knowledge of this stuff to make wise political decisions. We in the USA are notoriously, and proudly ignorant about of science. It is criminally negligent for a country with our awesome responsibilities to remain uneducated.

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