trigger, the thermonuclear would require no critical mass. As a fission bomb exploded, it disassembled its critical mass, at which point fissioning stopped. This disassembly process set a natural limit to the size of fission explosions of about one megaton. A thermonuclear explosion, however, if it could be made to ignite and sustain thermonuclear burning, would proceed like a nuclear version of a chemical explosion, continuing to burn so long as it had access to thermonuclear fuel. The stars — thermonuclear furnaces thousands and millions of times as large as the earth — made it obvious that there were no inherent physical limits to the size of thermonuclear explosions. The report of the conference just then getting underway would emphasize that the Super's “scale is limited — if it proceeds at all — only by the amount of deuterium fuel provided. Thermonuclear explosions can be foreseen which are not to be compared with the effects of the fission bomb, so much as to natural events like the eruption of [the] Krakatoa [volcano, in the Sunda Strait between Java and Sumatra in 1883]. .. Values like [the energy released in] the San Francisco earthquake may be easily attained.” During the war, Serber remembers, “on Edward Teller's blackboard at Los Alamos I once saw a list of weapons — ideas for weapons — with their abilities and properties displayed. For the last one on the list, the largest, the method of delivery was listed as ‘Backyard.’ Since that particular design would probably kill everyone on earth, there was no use carting it elsewhere.”
At the afternoon session on the first day of the Super Conference, a member of Teller's group discussed a tamper of beryllium oxide that was a feature of the fission trigger of the Super design (beryllium is fertile with loose neutrons that can be mobilized to enhance a fission chain reaction; most modern nuclear weapons have beryllium tampers). Cylindrical implosion was also discussed, probably as a way of incorporating the more efficient implosion mechanism into the pipelike configuration of the Super. According to Los Alamos records, “Dr. von Neumann suggested the ignition of a ‘Super’ bomb through the employment of an implosion process. Fuchs would claim — “laughingly,” an FBI interrogator notes — that it was in fact
The next day, April 19, mathematicians Nicholas Metropolis and Anthony Turkevich reviewed their ENIAC calculations of Super hydrodynamics. The terms of the calculations had been simplified from three dimensions to two and excluded significant physical processes that tended to cool the reaction by bleeding off energy. Under those idealized conditions, Metropolis and Turkevich reported, a Super fueled with deuterium would produce a substantial energy release. (Bethe and Teller had debated just such problems at the 1942 Berkeley summer conference, Serber remembers: “Edward first thought [the hydrogen bomb] was a cinch. Bethe, playing his usual role, knocked [Teller's idea] to pieces. Edward had figured the energy that would be released, how hot it would heat the gas, and so forth. Everything looked fine until Bethe pointed out that you would get radiation [from such intense heating]; you had to be in equilibrium with the black-body radiation, which goes up with the fourth power with temperature, drains the heat right off, and cools everything down. You start feeding [the fire] and bingo, everything goes into electromagnetic radiation. Edward hadn't allowed for that. Bethe thought of a mechanism that really drained the energy off fast — we called it the inverse Compton effect — that knocked Edward's calculations into a cocked hat, and they never actually recovered.” The inverse Compton effect was one of the significant physical processes excluded from the optimistic calculations that Metropolis and Turkevich reported.)
That afternoon and the following morning, another participant discussed the compression properties of deuterium and deuterium-tritium mixtures. Teller wrote later that the idea of compressing the hydrogen fuels with radiation was discussed at the Super Conference. (A fission bomb produces radiation — light, that is, primarily soft X rays — in such copious quantities that it is capable of significantly compressing matter.) It was not obvious how such a mechanism might work, Bradbury would recall. “I can remember very vividly in 1946 exploring in great detail this original idea with members of my technical staff. At the time we saw absolutely no way to make it into a usable system.”
Teller proposed an experimental program that second afternoon and discussed studying the various fusion reactions a Super might kindle — “tritium plus tritium, helium plus deuterium, hydrogen plus deuterium, and the like… ” As he had been in 1942 despite the wide safety factors that Bethe's cooling effects established, Teller was still concerned about the possibility of a fusion explosion igniting the atmosphere of the earth, which is predominantly nitrogen, in a thermonuclear Armageddon; he thought the “nitrogen plus nitrogen reaction” should certainly be studied.
At a final meeting on the morning of April 20, Teller opened the floor to a discussion of peaceful applications of thermonuclear fusion. Four years later, Fuchs could not even remember what the meeting had been about.
Teller and his thermonuclear group drafted a conference report that he circulated among the conferees in May 1946. It observed that deuterium was a more effective explosive than U235 or plutonium, yielding energy “several times that from the same weight of fissionable material,” while its unit cost, estimated at twenty cents per gram, was comparable not with U235 and plutonium, which cost several hundred dollars per gram, but with ordinary uranium. The report noted that hand calculations done in parallel with the ENIAC problem “indicated that… the system would ignite.” But whether, once ignited, thermonuclear burning would continue and propagate, the calculations had not “conclusively demonstrated.”
The report found in conclusion:
It is likely that a super-bomb can be constructed and will work.
Definite proof of this can hardly ever be expected and a final decision can be made only by a test of the completely assembled super-bomb…
The detailed design submitted to the conference was judged on the whole workable. In a few points doubts have arisen concerning certain components of this design… In each case, it was seen that should the doubts prove well-founded, simple modifications of the design will render the model feasible.
In a final paragraph, the report noted that undertaking the “Super Bomb Project” would use up a fair portion of the national nuclear-weapons budget for some years to come. It followed, the report argued, “that further decision in a matter so filled with the most serious implications as is this one can properly be taken only as part of the highest national policy.” It did recommend that tritium production should be organized, starting at a gram per day, to be increased as development required.
Serber remembers complaining that the draft he saw of the Super Conference report was far too optimistic. He thinks others may have complained as well. (Ulam comments that “the promising features of the plan were noticed and to some extent confirmed, but there remained great questions about initiation of the process and, once initiated, about its successful continuation.”) Serber recommended changes that he assumed would be incorporated into the final document. When the report was issued as quoted here on June 12, though it claimed to represent “essentially the unanimous opinions of those attending the conference,” Teller had left it virtually unchanged from the first optimistic draft.
The Super Conference report did not initiate a national policy discussion in the United States. At the time the report was issued, weapons as destructive as earthquakes and volcanoes were not on the national agenda. No military requirement for such a weapon would be established for years to come. Bernard Baruch was putting the finishing touches on his sanction-heavy plan for the international control of atomic energy, which he would present to the United Nations on June 14 (beginning melodramatically, “We are here to make a choice between the quick and the dead”). Los Alamos was busy with the Bikini tests soon to commence, needed to improve what Bradbury called its “lousy” fission bombs — among other reasons, to develop one hot enough to serve as a thermonuclear blasting cap — and was still struggling to survive. The report gathered together the work that had been accomplished on a thermonuclear up to that point; for the next several years, Carson Mark's theoreticians would devote about half their time to thermonuclear calculations while the rest of the laboratory worked on improving atomic bombs.
Sometime in 1946, however, Soviet physicists Isai I. Gurevich, Yakov Zel-dovich, Isaak Pomeranchuk and Yuli Khariton prepared a special report for the Soviet government titled
