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Richard Rhodes on: The Superbomb Design Breakthrough
Richard Rhodes Q: Early in 1951 Stanislaw Ulam comes up with a new idea for a superbomb design. What do you know about that?

RR: At that particular time, after Ulam finished these calculations on the Super, he really was interested in making better atomic bombs, fission bombs. And he started thinking about how you could do that. The thing that limited the yield on the classic implosion type bomb (the spherical bomb with the explosive squeezing the plutonium or uranium core until it was a critical mass, and then you had a nuclear explosion), the thing that limited the yield was that you couldn't get a lot of compression with high explosives. It occurred to him that maybe you could use the blast from one atomic bomb to squeeze a second atomic core, and thereby get the much more enormous compression that you would get from this much more enormous explosion. So he called it an iterative scheme, meaning something that repeats. And in fact, he envisioned the possibility of one atomic bomb setting off a second core, which in turn set off a third core. Theoretically, you could chain these together and have a larger and larger yield. That was the basic idea that he had. And he played with that for quite some time.

But at some point (it seems to have been around the beginning of 1951, January) it occurred to Ulam that the same iterative scheme of using the blast from an atomic bomb to set off a second bomb, might be the answer for the hydrogen bomb. If that second piece were hydrogen fuel, then you might be able to heat it and compress it sufficiently to start a fusion reaction going...

So he went to see Teller. Before he talked to Teller, though, he talked to Carson Mark. He seems to have talked to Norris Bradbury (Oppenheimer's successor as director of the laboratory). Then he took the idea to Teller. Teller was immediately hostile. He didn't think it was a good idea. But as they talked about it and looked at the numbers, within about (he--Ulam says) about 30 minutes, Teller got more and more enthusiastic.

But Teller then was able to connect this idea presumably with the George shot, with the idea of using not the blast from an atomic bomb, which travels relatively slowly because it's matter (neutrons mostly), but the radiation from the bomb. X-rays from an exploding atomic bomb travel 10 feet in the time it takes the neutrons to travel 4 inches. So as Carson Mark told me later, he couldn't have avoided the radiation. It was there. You had to deal with it. And in the more sophisticated and efficient bombs that by then we had in our arsenal, there was a lot more radiation than had been true of the first bombs. So there it was. Teller saw that the radiation could be used, and that that would solve the whole problem of the whole thing blowing itself apart before you could get much reaction going. And that truly was the breakthrough.

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