On Saturday, November 17, 2001, at 12:37 AM, baptista@pccf.net wrote:

On Sat, 17 Nov 2001, Tim May wrote:

...

I'd guess that the "tall pipe" version is the most buildable of the basement nukes. (In a nutshell: a tall drainpipe, perhaps 40 feet tall. Set up in an apartment building, warehouse, etc. At the base the pipe is reinforced with copious amounts of concrete. The subcritical masses are at opposite ends of the pipe. The mass on top is piled on with several hundred pounds of ballast, to "tamp" the early critical mass action. To explode the bomb, drop the mass from the top of the pipe. The critical mass is briefly contained by the concrete collar around the pipe and the inertial mass above. Is it enough to produce a real chain reaction? Well, it's all relative. Still, not very efficient.)

I very much doubt terrorist would build an efficient bomb. Non of what we discussed is effcient. Your pipe idea is a very interesting example. But I think the point is made that harm can be done. Even if the mass does not go critical - it still means a few city blocks that will be inconvenienced from the resulting radiation. You pipe certainly would not go boom - but it would leave a mess of radioactivity in the area.

The idea _is_ for it to detonate, not just have a severe thermal excursion! The total "radioactivity" in a critical mass of fissionables is actually not all that great. (Not something I'd want in my backyard, and sure to produce panic, but not all that significant.) The point of a bomb is to get a _lot_ of those radioisotopes fissioning in a much shorter amount of time than usual. Without that chain reaction, the radioisotopes are just decaying at their normal very, very slow rate. (The reason uranium is so radioactively benign is that it's half life is several billion years for the most common isotope and pretty close to that for the U-235 form...the reason we still find both in nature, of course.) For the oft-discussed "radiological bomb" there is no need for U-235. In fact, shorter half-lived stuff like cesium-137 and even spent fuel rods would be better. Personally, this is much _less_ worrisome than biological weapons. If radioisotopes are spread over a few city blocks, for example, they can be cleaned up in various ways. Easy to detect with a Geiger counter (or scintillation counter), easy to vacuum up with HEPA filter units, all sorts of foaming agents and hoses and the whole decontamination apparatus. And if the Geiger counter is silent, it's all gone. A radiological bomb would result in an evacuation, and the usual panic by the sheeple who are afraid of atoms, but the cleanup would be straightforward. (Chernobyl was what it was because many tons, even hundreds of tons, of fuel rods were vaporized and/or burned. Not many terrorists could arrange for the vaporization/combustion of this much material.) --Tim May "As my father told me long ago, the objective is not to convince someone with your arguments but to provide the arguments with which he later convinces himself." -- David Friedman