When I arrived in Los Alamos in late June 1950, Stan Ulam and his associate Cornelius Everett were wrapping up a series of calculations using no more machinery than a desktop calculator. In the calculations, they subjected a quantity of deuterium, with varying enrichments of tritium, to an initial high temperature of the kind that might be provided by a fission bomb and traced what happened. Did the thermonuclear flame spread or die out? Did the temperature increase, hold its own, or diminish? They found that the temperature did not increase and the flame did not propagate, even with unrealistically large admixtures of the tritium elixir.{21}
Whether adding tritium is “realistic” or “unrealistic” is dictated by its cost. Tritium, with a twelve-year half life, is not found in nature in other than trace amounts. Making it takes a large and expensive reactor, one that, if not making tritium, could be making plutonium. So fueling a Super with, say, a 50-50 mixture of D and T appeared to be out of the question. Nevertheless, reactors did eventually make substantial quantities of tritium, which found use in both fission and fusion bombs—and, more to the point, combined fission-fusion bombs. I remember sitting in on a 1950 meeting in Los Alamos with a large map of the United States spread out before us. The fingers of the decision makers in the room pointed toward Aiken, South Carolina. Action was swift thereafter. In October 1950, President Truman asked DuPont to build reactors there, as it had done in Hanford, Washington, during the war.{22} Construction started in 1951, and eventually five reactors at what was called the Savannah River Site churned out both tritium and plutonium.{23} (Incidental to that task, the reactors also created neutrinos—actually antineutrinos—by the countless billion, and it was at Savannah River that Fred Reines and Clyde Cowan in 1956 achieved the first detection of these stunningly elusive particles. Reines—once my next-door neighbor in California—went to Stockholm in 1995 to be recognized with a Nobel Prize.)
At around the time that Ulam and Everett were wrapping up their calculations (and annoying Teller, whose body English had not been sufficient to stimulate encouraging results), Enrico Fermi, in Los Alamos for the summer, began a related series of “burning” calculations with the assistance of the talented Miriam Planck, and with Ulam playing an advisory role. Planck, using equations provided by Fermi, laboriously filled in the cells in a chart (literally a spreadsheet on paper), following the thermonuclear reactions in time and in at least one dimension (either radially in a sphere or axially in a cylinder). Their results were no more encouraging than those of Ulam and Everett.
I familiarized myself with what Ulam and Fermi were up to, and at the same time mastered the behemoth CPC with its instructions encoded on a stack of punched cards. There were several CPCs in Los Alamos and more at Sandia Labs in Albuquerque as well as in New York. For about twelve to eighteen months in 1950-51, the CPCs played an important role in thermonuclear calculations, serving as a bridge between the desk calculators and slide rules of the past and the electronic computers of the future. (More on those computers later.)
To some at the lab, these discouraging results meant that the Super as then envisioned was unlikely ever to become reality. To others, such as the driven optimists Teller and Wheeler and their retinue of young researchers, including me, the results only told us that more and better ideas were needed—on the geometry, the choice of fuel, the mode of ignition, the deployment of fission and fusion components. As I described in Chapter 1, one big, crucial idea—radiation implosion—did appear on the scene early the next year (March 1951) and changed everything. (Teller did say later that the Ulam-Everett calculations “proved” that the classical Super would not work,{24} although he reached no such conclusion at the time.)
Chapter 10
Calculating and Testing
In the nine months or so between the Ulam-Everett-Fermi-Planck[57] gloom and the Teller-Ulam rosy dawn, how did we occupy ourselves?
In two ways. First, by hammering away with new and more elaborate calculations on various versions of the Super and on alternative thermonuclear devices such as the layered alarm clock. Teller and Wheeler had been asked to gather together the results of these new calculations, along with summaries of all that had come before, for presentation to the September 1950 meeting of the AEC’s General Advisory Committee in Washington—an “as of this time” overview of all that was known or projected about thermonuclear weapons.
The request for such a report came in the form of a letter of July 19, 1950 from Oppenheimer, the GAC Chairman, to Norris Bradbury, the Lab Director.{1} In the letter, cleared in advance with AEC Chairman Gordon Dean,{2} Oppenheimer wrote:
They [four GAC members who visited Los Alamos earlier in July] have been deeply interested in the new, more quantitative work bearing on the superbomb, and profoundly impressed with the progress that the Laboratory has made in coming to grips with these problems. We all feel that it would be of the greatest help to the whole effort if we could have, in time for our next scheduled meeting on September 11, a quite informal account of the findings and views of the Laboratory on the superbomb problem.
After noting that the Lab might consider September too early for such a report because “new calculations will be in progress, many questions will be quite unanswered,” he added:
Nevertheless, we believe that the progress and clarification already achieved are so important to sound overall planning and evaluation that we feel it proper to press you to accede.
Oppenheimer knew quite well the state of the “superbomb” work—that the outlook was very discouraging, that the prospect for what we later called the classical Super was dismal, all the more so after the most recent calculations. Was this letter therefore entirely disingenuous, intended to engineer embarrassment for Teller? I don’t dismiss this as a possibility. These two titans had been at odds at least since 1943, when Teller wanted the wartime Los Alamos Lab to give more attention to thermonuclear weapons. And as recently as September 1949, when, in reaction to the just-announced Soviet atomic bomb, Teller phoned Oppenheimer to ask “What do we do now?” and Oppenheimer answered “Keep your shirt on.”{3}
I leave it to historians of science to unravel Oppenheimer’s motivations and decipher this letter (if indeed it needs deciphering). Neither I nor any other junior member of the team saw any evidence that it aroused suspicion in Teller or Wheeler. If it did, they kept it to themselves. As far as we could tell, they welcomed the request and the opportunity it afforded to summarize all that they knew or surmised about thermonuclear weapons. The rest of us—which means principally John Toll, Burt Freeman, and I—jumped in and found it exhilarating to be part of the effort to organize an overview of past results and possible future directions.
We had only a few weeks to throw the report together. By the time it was completed, in August 1950,{4} it had a slight obesity problem and we called it the “telephone book.” Even though it presented disappointing past calculations, the report, overall, was anything but pessimistic. Teller and Wheeler, by nature optimistic, still had high hopes and wanted to encourage the GAC to recommend continued high-priority work on thermonuclear weapons. After reviewing the report, the GAC said:{5}