the weekend Bohr drew his graphs. As far as Wigner was concerned, the time for such amateurism was over. He “strongly appealed to us,” says Szilard, “immediately to inform the United States government of these discoveries.” It was “such a serious business that we could not assume responsibility for handling it.”
At sixty-three George Braxton Pegram was a generation older than the two Hungarians and the Italian who debated in his office that morning. A South Carolinian who had earned his Ph.D. from Columbia in 1903 working with thorium, he had studied under Max Planck at the University of Berlin and corresponded with Ernest Rutherford when Rutherford was still progressing in fruitful exile at McGill. Pegram was tall and athletic, a champion at tennis well into his sixties, a canoeist when young who enjoyed paddling and sailing an eighteen-foot sponson around Manhattan Island. His interest in radioactivity may have been aroused by his father, a chemistry professor; “probably the most important problem before the physicist today,” the senior Pegram told the North Carolina Academy of Sciences in 1911, “is that of making the enormous energy [within the atom] available for the world's work.” The next year, as an associate professor of physics at Columbia, Pegram had written Albert Einstein encouraging him to come to New York to lecture on relativity theory. Pegram had brought Rabi and Fermi to Columbia, building the university's international reputation for nuclear research. He was gray now, with thinning hair, wire-rimmed glasses, protuberant ears, a strong, square, wide-chinned jaw. Radioactivity intrigued him still, but a university dean's well-worn conservatism counseled him to caution.
He knew someone in Washington, he told Wigner: Charles Edison, Undersecretary of the Navy. Wigner insisted Pegram immediately call the man. Pegram was willing to do so, but first the group should discuss logistics. Who would carry the news? Fermi was traveling to Washington that afternoon to lecture in the evening to a group of physicists; he could meet with the Navy the next day. His Nobel Prize should give him exceptional credibility. Pegram called Washington. Edison was unavailable; his office directed Pegram to Admiral Stanford C. Hooper, technical assistant to the Chief of Naval Operations. Hooper agreed to hear Fermi out. Pegram's call was the first direct contact between the physicists of nuclear fission and the United States government.
The next topic on the morning's agenda was secrecy. Fermi and Szilard had both written reports on their secondary-neutron experiments and were ready to send them to the
Pegram prepared a letter of introduction for Fermi to carry along to his appointment. It stated a hesitant case dense with hypotheticals:
Experiments in the physics laboratory at Columbia University reveal that conditions may be found under which the chemical element uranium may be able to liberate its large excess of atomic energy, and that this might mean the possibility that uranium might be used as an explosive that would liberate a million times as much energy per pound as any known explosive. My own feeling is that the probabilities are against this, but my colleagues and I think that the bare possibility should not be disregarded.
Thus lightly armed, Fermi departed to engage the Navy.
The debate was hardly ended, nor Wigner's long day done. He returned to Princeton with Szilard in tow for an important meeting with Niels Bohr. It had been planned in advance; John Wheeler and L6on Ro-senfeld would attend and Teller was making a special trip up from Washington. If Bohr could be convinced to swing his prestige behind secrecy, the campaign to isolate German nuclear physics research might work.
They met in the evening in Wigner's office. “Szilard outlined the Columbia data,” Wheeler reports, “and the preliminary indications from it that at least two secondary neutrons emerge from each neutron-induced fission. Did this not mean that a nuclear explosive was certainly possible?” Not necessarily, Bohr countered. “We tried to convince him,” Teller writes, “that we should go ahead with fission research but we should not publish the results. We should keep the results secret, lest the Nazis learn of them and produce nuclear explosions first. Bohr insisted that we would never succeed in producing nuclear energy and he also insisted that secrecy must never be introduced into physics.”
Bohr's skepticism, says Wheeler, concerned “the enormous difficulty of separating the necessary quantities of U235.” Fermi noted in a later lecture that “it was not very clear [in 1939] that the job of separating large amounts of uranium 235 was one that could be taken seriously.” At the Princeton meeting, Teller remembers, Bohr insisted that “it can never be done unless you turn the United States into one huge factory.”
More crucial for Bohr was the issue of secrecy. He had worked for decades to shape physics into an international community, a model within its limited franchise of what a peaceful, politically united world might be. Openness was its fragile, essential charter, an operational necessity, as freedom of speech is an operational necessity to a democracy. Complete openness enforced absolute honesty: the scientist reported
The next afternoon Fermi turned up at the Navy Department on Constitution Avenue for his appointment with Admiral Hooper. He had probably planned a conservative presentation. The contempt of the desk officer who went in to announce him to the admiral encouraged that approach. “There's a wop outside,” Fermi overheard the man say. So much for the authority of the Nobel Prize.
In what Lewis Strauss, by now a Navy volunteer, calls “a ramshackle old board room” Hooper assembled an audience of naval officers, officers from the Army's Bureau of Ordnance and two civilian scientists attached to the Naval Research Laboratory. One of the civilians, a bluff physicist named Ross Gunn, had watched Richard Roberts demonstrate fission in the target room of the 5 MV Van de Graaff at the DTM not long after Fermi passed through at the time of the Fifth Washington Conference. Gunn worked on submarine propulsion; he was eager to learn more about an energy source that burned no oxygen.
Fermi led his auditors through an hour of neutron physics. If the notes of one of the participants, a naval officer, are comprehensive, Fermi emphasized his water-tank measurements rather than Szilard's more direct ionization-chamber work. New experiments in preparation might confirm a chain reaction, Fermi explained. The problem then would be to assemble a sufficiently large mass of uranium to capture and use the secondary neutrons before they escaped through the surface of the material.
The officer taking notes interrupted. What might be the size of this mass? Would it fit into the breech of a gun?
Rather than look at physics down a gun barrel Fermi withdrew to the ultramundane. It might turn out to be the size of a small star, he said, smiling and knowing better.
Neutrons diffusing through a tank of water: it was all too vague. Except to alert Ross Gunn, the meeting came to nothing. “Enrico himself… doubted the relevance of his predictions,” says Laura Fermi. The Navy reported itself interested in maintaining contact; representatives would undoubtedly visit the Columbia premises. Fermi smelled the condescension and cooled.
March 17 was a Friday; Szilard traveled down to Washington from Princeton with Teller; Fermi stayed the weekend. They got together, reports Szilard, “to discuss whether or not these things” — the
The following month, on April 22, Joliot, von Halban and Kowarski published a second paper in
