Tim May wrote: [...]
As I made clear in my post, it's not _my_ idea. It's one of the standard "basement nuke" proposed designs.
Same here of course. [...]
I will mention that Ken Brown's "many pieces along the length of the pipe" is the worst way to do this: it buys nothing over the two pieces approach and it causes all sorts of problems with the pieces getting too hot as they come together on the way down.
The only reason for mentioning it was that it is perhaps a way people who somehow got hold of the the fissile material, but otherwise had access only to stuff you could pick up on the street, could bodge something together that that would scare others. I'd have no expectation of a nuclear explosion from such a rig. The only advantage is that it is cheap and can be set up in a few hours and (perhaps) might make a truly scary booby-trap. It might be even more effective if it didn't have a timer. A few kilos of fissile uranium literally hanging by a thread in a housing project would make the TV news worldwide.
(For example, the penultimate chunk falling toward the ultimate chunk...likely to already be melting and spraying molten U-235 inside the pipe. Just another fizzle. And fizzles are not very interesting, for reasons I stated. A way too expensive way to spread mere radiological terror, which could be done much more cheaply and easily by taking spent fuel rods and blowing them up, or just by grinding up spent fuel rods or other nuclear waste and then dumping it out of a plane over a city.)
Back to Heinlein again... Ken Brown Shit. If the UK government passes this law they are proposing then this email would probably count as illegal. And anonymous postings are often so tedious.