were working on the problem of the fusion bomb… Gamow placed a ball of cotton next to a piece of wood. He soaked the cotton with lighter fuel. He struck a match and ignited the cotton. It flashed and burned, a little fireball. The flame failed completely to ignite the wood, which looked just as it had before — unscorched, unaffected. Gamow passed it around. It was petrified wood. He said, “That is where we are just now in the development of the hydrogen bomb.’”
From October on, Bethe continues, while the President of the United States warned the world that he was prepared to use atomic bombs in Korea and the Chinese armies pushed down the Korean peninsula, Teller “was desperate”:
He proposed a number of complicated schemes to save [the classical Super], none of which seemed to show much promise. It was evident that he did not know of any solution. In spite of this, he urged that the Laboratory be put essentially at his disposal for another year or more after the
Teller viewed his position far more grandly. He had stuck by his guns, he wrote Ernest Lawrence at the beginning of December; the criticism was unfair. All he was trying to do was to make sure that a valuable addition to the nation's security was not neglected. “Dr. Teller was never one to keep his candles hidden under bushels,” AEC commissioner Sumner Pike would testify. “He was kind of a missionary. I might say that perhaps John the Baptist is a little overexaggeration. He always felt that [his] program had not had enough consideration… I would guess that it would have suited him completely if we had taken all the resources we had and devoted [them] to fusion bombs.” Los Alamos theoretician Charles Critchfield, a levelheaded man, was equally blunt. “Teller has a messianic complex,” he concluded.
Motivated partly by distaste for Teller's posturing, Stanislaw Ulam had set out systematically to determine if the design upon which the Hungarian-born physicist had insisted with such vehemence for more than five years was simply a fantasy or had some useful connection to physical reality. Ulam and his colleagues demonstrated that the Super's connection was probably tenuous at best. Before the end of the year, John von Neumann's ENIAC calculations came in to add additional weight to that conclusion. “Why did we still follow the classical Super?” Bethe asks of that depressing autumn. “Well, for one thing, it had not been proved that it was dead. For another thing, nobody had an alternative and better idea.” Then, Bethe concludes, Ulam's work plus the von Neumann calculations “proved that the Super was dead.”
Teller might cling to his fantasy of a thermonuclear weapon of unlimited power; for Ulam, the long effort of calculation had been a necessary clearing away. When the Polish-born mathematician finished his Super calculation work, he began thinking about how fission bombs could use the still-scarce US supply of U235 and plutonium more efficiently. Implosion, by compressing a subcritical core, made it possible to get a bigger bang from a smaller amount of fissile metal than was possible with a gun design, which simply assembled a critical mass without compression, but the degree of compression available for implosion was limited by the force that could be generated from high explosives. In December 1950, Ulam thought of a way to increase implosion compression by orders of magnitude. He called the arrangement “hydrodynamic lensing.” The fluid (“hydro”) Ulam had in mind to power (“dynamic”) his implosion system was the shock wave from an atomic bomb — primarily, he writes, the “enormous flux of neutrons.” For a short time during a fission bomb explosion, Ulam pointed out, “one has… a neutron ‘gas'… present together with the other [fission fragment] nuclei at densities comparable to those of ordinary solids.” He took his new idea to Carson Mark. “The first thing that Ulam described to me,” Mark remembers, “at the beginning of 1951, was using fission for compression — much greater compression than any other method we were aware of allowed. You could compress a little piece of fissionable material, for example, and make it explode.”
To use fission for compression, Ulam realized, would require staging: one bomb, which came to be called a “primary,” would set off a second, physically separate bomb, a “secondary.” Theoretically any number of bomb assemblies could be set off this way in succession. The idea was elegant but premature; Los Alamos had no immediate use for it. It stayed with Ulam into the new year. Sometime in January, he received a memorandum from Darol Froman asking “various people what should be done with the whole ‘Super’ program. While expressing doubts about the validity of Teller's insistence on his own particular scheme, I wrote to Froman that one should continue at all costs the theoretical work, that a way had to be found… ” Shortly after responding to Froman's memorandum, Ulam writes, he saw a way to apply his “iterative” scheme to a thermonuclear. He says he then “put his thoughts in order and made a semi-concrete sketch.” Frangoise Ulam never forgot the moment she heard:
Engraved on my memory is the day when I found him at noon staring intensely out of a window in our living room with a very strange expression on his face. Peering unseeing into the garden, he said, “I found a way to make it work.” “What work?” I asked. “The Super,” he replied. “It is a totally different scheme, and it will change the course of history.”
Frangoise, who “had rejoiced that the ‘Super’ had not seemed feasible,” was “appalled by this news.” She asked her husband what he intended to do:
He replied that he would have to tell Edward. Knowing how unpleasant Teller had been, I ventured that maybe he ought to test his idea on someone else first. He did. That very afternoon, I think, he went to see Carson [Mark]. But the meeting was not very satisfactory, for when, in the evening, I asked him how it had gone, he only shrugged his shoulders and said that Carson was awfully busy. Too busy, I surmised, to pay much attention to what he was trying to tell him. (Stan could be oblique or Pythic sometimes, especially when particularly preoccupied with a topic he assumed his interlocutor was on the same wavelength [with]… ) At any rate, he had to go to Teller after all.
Ulam had gone on to see Norris Bradbury after he talked to Mark that afternoon, he writes, “and mentioned this scheme.” Bradbury had been more welcoming. “He quickly grasped its possibilities and at once showed great interest in pursuing it. The next morning, I spoke to Teller.” Ulam probably spoke to Teller sometime during the last week in January 1951.
To apply his idea of staging to the thermonuclear, Ulam had to work through the question of compressing the thermonuclear fuel, which is what his shock-implosion system would do. Teller's classical Super was essentially a system for heating uncompressed liquid deuterium to the point, Teller hoped, when it would sustain thermonuclear burning. The problem with the classical Super was that radiation carried heat away from the fuel faster than thermonuclear reactions could replace it. Compressing the fuel would not obviously improve that situation. The question had come up so often, says Carson Mark, that Teller had worked it into his standard briefing on Super design. “Teller used to say, ‘Compression makes no difference.’ That was number two on his list. He instilled that notion in many people.”
Teller himself explains his attitude toward compression by referring to what he calls a similarity relation. Suppose, he says, you have a unit of deuterium in its normal state and another unit that is compressed to one thousand times the first unit's density. Both, he believed, would react the same way if other variables — temperature, hydrodynamic velocity and so on — were the same. The compressed fuel is a thousand times more dense, so its reaction rate is a thousand times faster. But since everything is a thousand times closer together, the amount of time required for the reactions to propagate from one atom to the next is a thousand times shorter. “You can see,” Teller concludes, “that all the reactions that depend on a collision between a pair of particles will proceed in a similar way because in the comparison between reaction time and expansion time, both have been equally reduced. The course of the reaction is the same, with the ‘insignificant’ change of a thousandfold contraction of time… ” That is, everything would go faster, but the outcome — including, in the case of thermonuclear burning, the fatal cooling of the fuel mass by radiation loss — would otherwise be similar.
“The theorem is not quite precise,” however, Teller continues. A three-body reaction comes into play with compression, he says — the collision of an electron, a nucleus and a photon with absorption of the photon, which
