3 ms·

Google "Farm Hall transcripts", that's what you're thinking of. But you're quite right. Heisenberg used an incredibly faulty method of calculating critical mas

Google "Farm Hall transcripts", that's what you're thinking of. But you're quite right. Heisenberg used an incredibly faulty method of calculating critical mass. And everyone around him simply deferred to his expertise. His method involved considering a branching tree of neutron chain reactions inside a sphere of fissile material, and if this tree can grow to include about 1 mole of material then that should be about enough to release enough energy for a "bomb". The reality is that it's completely unnecessary for an entire neutron chain-reaction tree to be encompassed within fissile material. All that matters is that on average from generation to generation there is a multiplication of neutrons, which will then grow geometrically incredibly rapidly. And that can happen even with many "branches" of the tree leaving the sphere and not contributing to future reactions.

paulmd 11y ago
He also "proved" (incorrectly) that graphite was not an appropriate moderator. Which ruled out bombs pretty much entirely. In hindsight, he was actually blatantly incorrect. Dude knew it was possible and convinced the rest of the German scientists it wasn't, for long enough to make a difference. If you read between the lines, he's almost gloating in that transcript. "On the other hand the whole heavy-water business, which I did everything I could to further, cannot produce an explosive." "We wouldn't have had *the moral courage* to recommend to the government in the spring of 1942 that they should employ 120,000 men just for building the thing up." "The point is that the whole structure of the relationship between the scientist and the state in Germany was such that although we were not *100% anxious* to do it, on the other hand we were so little trusted by the state that *even if we had wanted to do it*, it would not have been easy to get it through." "Well, that's not quite right. I would say that I was absolutely convinced of the possibility of our making a uranium engine, *but I never thought we would make a bomb, and at the bottom of my heart I was really glad that it was to be an engine and not a bomb. I must admit that*." That's a Bill Gates level of finely-parsed deposition right there.

paulmd 11y ago

He also "proved" (incorrectly) that graphite was not an appropriate moderator. Which ruled out bombs pretty much entirely. In hindsight, he was actually blatantly incorrect. Dude knew it was possible and convinced the rest of the German scientists it wasn't, for long enough to make a difference. If you read between the lines, he's almost gloating in that transcript. "On the other hand the whole heavy-water business, which I did everything I could to further, cannot produce an explosive." "We wouldn't have had *the moral courage* to recommend to the government in the spring of 1942 that they should employ 120,000 men just for building the thing up." "The point is that the whole structure of the relationship between the scientist and the state in Germany was such that although we were not *100% anxious* to do it, on the other hand we were so little trusted by the state that *even if we had wanted to do it*, it would not have been easy to get it through." "Well, that's not quite right. I would say that I was absolutely convinced of the possibility of our making a uranium engine, *but I never thought we would make a bomb, and at the bottom of my heart I was really glad that it was to be an engine and not a bomb. I must admit that*." That's a Bill Gates level of finely-parsed deposition right there.