japan observation ramble wrapup extravaganza!
Calculating the critical mass required for the bomb to work was a pretty big deal, and as Einstein implied, potentially a deal-breaker in wartime. Heisenberg mis-calculated it, calculating for U-238 instead of a concentration of U-235. When he met secretly with Neils Bohr, Bohr might or might not have told him that he miscalculated, and Heisenberg might or might not have sustain the miscalculation on purpose, to foil the Nazi bomb. If I recall correctly, Bohr claimed Heisenberg was incompetent to run the Nazi's bomb program, while Heisenberg claimed he was sabotaging it. The world continues to wonder to this day.
Meanwhile, the Japanese made the calculation as well, and decided that creating that much U235 was beyond their industrial capacity during wartime, and IIRC believed that it would also be beyond the capacity of the other belligerent nations for the forseeable future.
--LAN3 Fri Mar 28 09:27:41 2008
One of the charts I remember was the production of Uranium.

I wonder how much the atomic bomb was a "mental" challenge, so to speak, and how much it was engineering, and how much it was just plain old production, as you imply here...
--Kirk Fri Mar 28 09:59:44 2008
The major challenge for production was the uranium separation. There was a whole lot of research that went into the understanding of the density of uranium required for the supercritical explosive reaction, and likewise what was appropriate for a mere critical chain reaction (such as was demonstrated by CP-1, the reactor built in Chicago). A lot of the conceptual work was done in the years before the war, when fission was first observed and theorized. They also had to design the reaction's trigger, some oddball element set at the center to give off a handful of powerful neutrons. 
There was one other major engineering task, but it's a military thing-- they had to design the explosive lenses and get them shaped perfectly, and also design teh switches. For Hiroshima's "Little Boy," all they had to do was design a gun that could fire the uranium slug fast enough. (Originally the army artillary corps told the Los Alamos gang that the gun would have to be 17' long and weigh several tons. That was before they understood that it only had to be fired once.)

Anyway, the fact is that production, engineering, and materials are what keep nations from building them today-- The plans are easy, but getting the pieces to build it is heavily regulated, especially if you've got UN sanctions hanging over your head.
--LAN3 Fri Mar 28 12:09:41 2008
Yeah, I noted with a kind of sick geek fascination the differences between Little Boy, firing uranium into uranium via a kind of one time internal cannon, and Fat Man, which is kind of a big implosion, and wondered which was "better"
--Kirk Fri Mar 28 13:51:50 2008
Could you elaborate on the "Reading Rooms in libraries" thing?
--LAN3 Fri Mar 28 20:52:21 2008
Err, in museums, right?

Every museum (admitedly mostly modern art ones) had a small reading room, seemingly mostly stocked with a big variety of art magazines. Couldn't remember if USA museums had that as well but didn't think so.
--Kirk Sat Mar 29 01:56:39 2008
Heh, yes. Reading rooms in libraries doesn't seem as unlikely. Dur. Thanks! I don't think I've ever seen anything like that in the US. Speaking as someone who works with a lot of science-museum folks-- which granted have a younger audience than classy art musea, such a room would be an encouragement for chaparoning parents to sit around and read/gab etc. and in general ignore their charges.
--LAN3 Sat Mar 29 09:11:16 2008

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