By the autumn of 1941, without official support, Dunning and Booth had nevertheless made significant progress. They had switched to brass barriers from which the zinc had been etched (brass is an alloy of copper and zinc; etching away the zinc made the material porous). In November, the month after Compton's visit, they would successfully enrich a measurable quantity of uranium with their equipment.
Compton traveled next to Princeton to see Eugene Wigner, who had been working closely with Fermi. Wigner clarified for Compton the difference between fast- and slow-neutron fission. He endorsed the uranium-graphite system Fermi was developing as a method for producing 94. “He urged me,” writes Compton, “almost in tears, to help get the atomic program rolling. His lively fear that the Nazis would make the bomb first was the more impressive because from his life in Europe he knew them so well.”
Back in Chicago Compton talked to Glenn Seaborg, who had come east from Berkeley at Compton's request. Seaborg was confident he could devise a large-scale, remote-controlled technology for separating 94 chemically from uranium.
Armed with this new round of information Compton called a meeting of his committee for October 21 in Schenectady. He prepared for the meeting by writing a draft report. A letter came from Lawrence saying he wanted to bring along Robert Oppenheimer: “I have a great deal of confidence in Oppie, and I'm anxious to have the benefit of his judgment in our deliberation.” Conant had scolded Lawrence at Compton's fireside when he learned that Lawrence had asked Oppenheimer, still an outsider, for help with theory, but now Lawrence's request was granted.
A dispute between Lawrence and Oppenheimer about what Lawrence called the theoretician's “leftwandering activities” almost excluded him from the atomic bomb project. Oppenheimer, married now to the former Katherine Puening, known as Kitty, with a six-month-old son, had begun to wish for assignment. “Many of the men I had known went off to work on radar and other aspects of military research,” he testified later. “I was not without envy of them.” He learned the price of admission when he invited Lawrence to an organizational meeting at his elegant new home on Eagle Hill for a professional union, the American Association of Scientific Workers, of which Arthur Compton, among others, was a senior member. Lawrence wanted no part in any “causes and concerns,” as he called political activities, and barred his staff as well: “I don't think it's a good idea,” he told them. “I don't want you to join it. I know nothing wrong with it, but we're planning big things in connection with the war effort, and it wouldn't be right. I want no occasion for somebody in Washington to find fault with us.” Oppenheimer was not so easily put off; he debated Lawrence's point, arguing that humanity was everyone's responsibility and that the more fortunate should help “underdogs.” The Nazis came first, Lawrence countered. He told Oppenheimer about Conant's scolding. Oppenheimer reserved judgment. The October 21 meeting, where he could measure the scientific leaders of the uranium program against his own formidable gifts, changed his mind. “It was not until my first connection with the rudimentary atomic-energy enterprise,” he testifies, “that I began to see any way in which I could be of direct use.” When he saw his way to war work he quickly sacrificed his underdogs, writing Lawrence on November 12:
I… assure you that there will be no further difficulties at any time with the A.A.S.W… I doubt very much whether anyone will want to start at this time an organization which could in any way embarrass, divide or interfere with the work we have in hand. I have not yet spoken to everyone involved, but all those to whom I have spoken agree with us: so you can forget it.
Lawrence opened the Schenectady meeting by reading Oliphant's summary of the MAUD Report. Compton followed with a review based on his October travels. Oppenheimer weighed in during the discussion of U235's critical mass with an estimate of 100 kilograms, 220 pounds, close to Fermi's estimate of 130,000 grams. “Kistiakowsky,” writes Compton, “explained the great economic advantage of being able to deliver a heavy blow with a bomb carried by a single plane.”
But Compton was distressed to discover he could not move the engineers on the review committee — the practical souls Bush had insisted be added to bring the NAS reviews down to earth — to estimate either how much time it would take to build a bomb or how much the enterprise would cost:
With one accord they refused… There weren't enough data. The fact was that they had before them all the relevant information that existed, and some kind of answer was needed, however rough it might be, for otherwise our recommendation could not be acted upon. After some discussion, I suggested a total time of between three and five years, and a total cost… of some hundreds of millions of dollars. None of the committee members objected.
So the American numbers came out of a scientist's hat, as the British numbers had. Atomic energy was still too new for engineering.
If Compton was distressed by the refusal of commitment, Lawrence was appalled. Within twenty-four hours he mailed the committee chairman a bracing challenge edged with threat:
In our meeting yesterday, there was a tendency to emphasize the uncertainties, and accordingly the possibility that uranium will not be a factor in the war. This to my mind, was very dangerous…
It will not be a calamity if, when we get the answers to the uranium problem, they turn out negative from the military point of view, but if the answers are fantastically positive and we fail to get them first, the results for our country may well be tragic disaster. I feel strongly, therefore, that anyone who hesitates on a vigorous, all-out effort on uranium assumes a grave responsibility.
But Compton had already been threatened by an expert, Vannevar Bush, and knew his duty well, though he did not yet know that Bush was already committed to expedition and expansion. He had difficulty estimating “the destructiveness of the bomb.” The calculation “involved problems of gas pressure, specific heats at hitherto unknown temperatures, the transmission of radiations and particles through the material, and forces of inertia.” He asked Gregory Breit for help. Breit was even more obsessed with secrecy than Briggs. “No help was forthcoming,” says Compton, gritting his teeth. He turned then to Oppenheimer. “I had known ‘Oppie’ for some fourteen years and had found him most competent in seeing the essentials of an intricate problem and in interpreting what he saw. So I was glad to get a letter from him with helpful suggestions.” Through the end of October Compton worked on.
At Leipzig in September Werner Heisenberg received the first forty gallons of heavy water from Norsk Hydro and immediately prepared another chain-reaction experiment like the unsuccessful effort at the Virus House in Dahlem the year before: a thirty-inch aluminum sphere filled with alternating layers of heavy water and uranium oxide, more than three hundred pounds of it, arranged around a central neutron source, the sphere itself then immersed in water in a laboratory tank. This time Heisenberg found some increase in neutrons, enough to extrapolate eventual success. The German laureate knew now from the work of von Weizsacker and Houter-mans that a sustained chain reaction in natural uranium would breed element 94. “It was from September 1941,” he remarks in consequence, “that we saw an open road ahead of us, leading to the atomic bomb.”
He decided to talk to Bohr. To what end he thought Bohr might help him he never unambiguously explained. His wife Elisabeth believes “he was lonely in Germany. Niels Bohr had become a father figure to him…
He thought that he could talk about anything with Bohr… The advice of an older friend, more experienced in human and political affairs, had always been important to him.” He “saw himself confronted with the spectre of the atomic bomb,” Elisabeth Heisenberg explains, “and he wanted to signal to Bohr that Germany neither would nor could build a bomb… Secretly he even hoped that his message could prevent the use of an atomic bomb on Germany one day. He was constantly tortured by this idea… This vague hope was probably the strongest motivation for his trip.”
Heisenberg and von Weizsacker attended a scientific meeting in Copenhagen at the end of October, a meeting Bohr routinely boycotted as he boycotted all joint Danish and German activities, to emphasize his refusal to collaborate. He was willing to see Heisenberg, however, and received him, according to the German physicist's wife, “with great warmth and hospitality.”
Heisenberg saved his crucial conversation for a long evening walk with Bohr through the brewery district around the Carlsberg House of Honor. “Being aware that Bohr was under the surveillance of the German political authorities,” he recalled after the war, “and that his assertions about me would probably be reported to Germany, I
