News You Can Bruise for 2008 July 28

Mon Jul 28 2008 22:08 The Making of the Atomic Bomb: A huge book you should read. Bought on Rachel Chalmers's recommendation though I can't find a link. (Update: aha) Some tidbits:

• Richard Feynman barely shows up in the book at all. He was a grad student at the time.
• The main justification scientists gave for working on the atomic bomb project was that it would save lives by shortening the war. This is the same rationale the previous generation of scientists gave for working on poison gas.
• A common anecdote brought out around the anniversaries of the Trinity test is that "Enrico Fermi... offered side odds on the bomb destroying all life on the planet", by igniting the atmosphere. This is true but misleading. Here's Leslie Groves (p664):

  I had become a bit annoyed with Fermi... when he suddenly offered to take wagers from his fellow scientists on whether or not the bomb would ignite the atmosphere, and if so, whether it would merely destroy New Mexico or destroy the world. He had also said that after all it wouldn't make any difference whether the bomb went off or not because it would still have been a well worth-while scientific experiment. For if it did fail to go off, we would have proved that an atomic explosion was not possible."

  1. It had been known for some time that a fission reaction wouldn't really ignite the atmosphere. This would have happened by causing a fusion chain reaction that burned atmospheric nitrogen as fuel, but it turns out the atmosphere doesn't work that way. (But see below for more.) 2. If the Trinity bomb didn't go off it wouldn't actually have proved anything; it probably have been due to an engineering problem, and Fermi knew this. So Fermi was just blowing off steam by being facetious.

  There's a paper that says basically "for ignition to occur, our measurements of various physical phenomena would have to be off by a very large factor, but don't blame us if it does ignite the atmosphere through some unknown mechanism." Pretty standard ass-covering. This isn't something nobody had thought about until Fermi started taking bets on it.

  Apropos that, here's a quote from Albert Speer (p404):

  Hitler had sometimes spoken to me about the possibility of an atom bomb, but the idea quite obviously strained his intellectual capacity. He was also unable to grasp the revolutionary nature of nuclear physics... Actually, Professor Heisenberg had not given any final answer to my question whether a successful nuclear fission could be kept under control with absolute certainty or might continue as a chain reaction. Hitler was plainly not delighted with the possibility that the earth under his rule might be transformed into a glowing star.

  I'm also pretty sure this nitrogen-fusion chain reaction is what Brian Moriarty had in mind in that part of Trinity which if you don't know about it I've said too much already.

• After Heisenberg met with Bohr in 1941, the Allies had all the necessary information to deduce that the German bomb project was pretty much dead. Heisenberg's design sucked, and the Germans couldn't make much plutonium. But the scientists didn't need to know that second fact, and it looks like they drew the wrong conclusion from to the first: that the Germans "had succeeded in keeping their aims secret, even from a scientist as wise as Bohr." I think this was the point at which the scientists building the bomb lost their voice in how it might be used, Bohr's efforts notwithstanding.
• The Japanese atomic program was even worse off. It didn't help that the military liason, Nobuuji, was "as innocent of nuclear physics as a stone." Unauthorized excerpt from book. I'll fair-use this quotation from p582:

  Nobuuji: If uranium is to be used as an explosive, 10 kg is required. Why not use 10 kg of a conventional explosive?
  Nishina: That's nonsense.

  Then he slapped Nobuuji on the top of the head.

• This diagram of the foam plasma pressure technique for burning hydrogen in an H-bomb is beautiful. (Nb. no such diagram is in TMotAB, and real H-bombs probably use a technique whose diagram is less beautiful.)