Pandora's Keepers (9 page)

At Roosevelt’s request, Watson directed the creation of an Advisory Committee on Uranium to explore the feasibility of an American atomic bomb program and report its findings to the president. Lyman Briggs, the director of the National Bureau of Standards, was appointed the committee’s chairman. Although Briggs was a physicist, his interests and experience were not in nuclear physics. Moreover, he was conservative by nature, accustomed to operating—as most bureaucrats do—in a slow, cautious, and methodical manner. For Briggs, fission’s possibilities had to be soberly measured against opportunities in other fields.
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The Uranium Committee met for the first time on October 21, 1939—ten long months after the discovery of fission in Germany. Sachs saw to it that Szilard and Teller were invited to the meeting. Fermi was also invited, but he refused to attend; his experience with Admiral Hooper and the navy made him unenthusiastic about another meeting with government bureaucrats. Fermi did, however, authorize Teller to speak on his behalf.

Szilard opened the meeting by emphasizing the possibility of creating a chain reaction in a uranium-graphite “pile” (or nuclear reactor). He explained to the committee that each time a uranium nucleus split apart, it released tremendous energy. But fission would not occur if one had to keep firing neutrons from an external source at the uranium atoms to break them up. If, on the other hand, the uranium atom released neutrons as it split, then these neutrons could go on and break up other nuclei. The neutrons from these disintegrations would trigger more, producing a chain of fissions. But neutrons had a less than 1 percent chance of fissioning a nucleus of natural uranium—thus no chance for a chain reaction. Neutrons needed to be slowed down. Slow neutrons had a more than 50 percent chance of fissioning a uranium nucleus—thus producing a chain reaction. The best way to slow neutrons was to use a “moderator,” which absorbed neutrons. The best moderator was graphite, whose carbon molecules absorbed about 10 percent of neutrons.

All of this sounded terribly exotic to the bureaucrats gathered around the table. The ordnance expert at the meeting, Lieutenant Colonel Keith Adamson, an officer at the army’s Aberdeen Proving Ground in northern Maryland, sneered at the idea of an atomic bomb—it was sheer fantasy. The colonel told Szilard and Teller in no uncertain terms that he did not believe “all this junk about complicated inventions.” “At Aberdeen,” he went on, ridiculing the physicists, “we have a goat tethered to a stick with a ten-foot rope, and we have promised a big prize to anyone who can kill the goat with a death ray. Nobody has claimed the prize yet.”
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Adamson then proceeded to lecture Szilard and Teller about scientific boondoggles in wartime. “He told us that it was naive to believe that we could make a significant contribution to defense by creating a new weapon,” recalled Szilard. “He said that if a new weapon is created, it usually takes two wars before one can know whether the weapon is any good or not. Then he explained rather laboriously that in the end it is not weapons which win the wars, but the morale of the troops.”
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Teller listened to Adamson with mounting frustration and anger. He had studied in Germany for many years and understood their military technology better than most—certainly better than the colonel. Finally he exploded. “If it is morale and not weapons that wins wars,” Teller said, his voice rising as his accent thickened, “then why does the Army need such a large arms budget? Perhaps its funding can be cut.” “All right, all right,” Adamson replied, “you’ll get your money.”
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The Uranium Committee authorized all of $6,000 to purchase graphite, though Szilard and Fermi would not actually receive the money for several months. Briggs sent a report of the meeting to President Roosevelt on November first. He heard from the White House on November seventeenth. The president had read the report and wanted to keep it on file. “On file” is where it languished well into 1940.

Szilard and Teller left their meeting with the Uranium Committee frustrated and dejected. They felt trapped in a dilemma: to determine whether a nuclear chain reaction could be the basis for the development of an atomic bomb required a thorough scientific investigation; such an investigation required significant financial support, but the Uranium Committee would not give such support without compelling evidence suggesting probable success. Since they could not guarantee that a bomb would be available for wartime use, they could not attract the money for vital chain-reaction experiments. They felt as if they were “swimming in syrup.”
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Months passed and nothing happened. Szilard’s frustration turned to anger. He decided to write a scientific paper about a chain-reacting uranium-graphite pile and threaten to publish it unless the government promised to move on fission research. The ploy worked. Within weeks of making his threat known, Columbia University received a grant of $6,000 for the purchase of graphite.
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This allowed Szilard and Fermi to begin their experiments. They started by addressing two problems: the absorption rate of graphite and its effectiveness in slowing down neutrons. They set up the graphite in a square column several feet thick. Then they arranged lumps of uranium in a lattice configuration throughout the column, placed a neutron source inside the column, and measured the neutron activity with Geiger counters. The results led Szilard and Fermi to conclude that a very large pile would be needed to create and sustain a chain reaction. What is more, impurities commonly found in uranium and graphite would have to be eliminated because these impurities hungrily absorbed neutrons. All of this meant that a chain-reacting uranium-graphite pile would be very expensive in both materials and labor.

Meanwhile, Szilard traveled again to Princeton to see Einstein. They prepared a second letter for President Roosevelt that emphasized the secret German uranium research underway at the Kaiser Wilhelm Institute, which they had learned about from a Jewish chemist, Peter Debye, who had recently been expelled from the institute. This second Einstein letter also stressed that Berlin had assumed direct responsibility for fission research and was stepping up its efforts to achieve a breakthrough.
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In March 1940 Sachs sent the letter to FDR, who ordered the White House to consult the Uranium Committee. Briggs and Adamson cautiously said that nothing more should be done, pending the outcome of Fermi’s and Szilard’s work on neutron absorption in graphite. Bureaucratic caution prevailed once again.

Meanwhile, security officials busily developed a mind-set of distrust toward Szilard, Teller, Fermi, and other refugee physicists “of queer types and backgrounds.”
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Agents categorized them as “aliens,” or in the case of Fermi, who came from Italy—an Axis country—as an “enemy alien.” A confidential report prepared by Army Intelligence in the summer of 1940 offered the following assessment of Fermi and Szilard:

(1) ENRICO FERMI. Department of Physics, Columbia University, New York City, is one of the most prominent scientists in the world in the field of physics. He is especially noted for breaking down the atom. He has been in the United States for about eighteen months. He is an Italian by birth and came here from Rome. He is supposed to have left Italy because of the fact that his wife is Jewish. He has been a Nobel Prize winner. His associates like him personally and greatly admire his intellectual ability. He is undoubtedly a Fascist. It is suggested that, before employing him on matters of a secret nature, a much more careful investigation be made. Employment of this person on secret work is not recommended.

(2) MR. SZELARD. It is believed that this man’s name is SZILLARD. He is not on the staff of Columbia University, nor is he connected with the Department of Physics in any official capacity. He is a Jewish refugee from Hungary. It is understood that his family were wealthy merchants in Hungary and were able to come to the United States with most of their money. He is an inventor, and is stated to be very pro-German, and to have remarked on many occasions that he thinks the Germans will win the war. It is suggested that, before employing him on matters of a secret nature, a much more careful investigation be made. Employment of this person on secret work is not recommended.
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Allegedly derived from “highly reliable” sources, the report was riddled with errors. To security investigators, Szilard and Fermi were simply foreigners with strong accents, suspicious backgrounds, and a string of fanciful ideas. Briggs informed Szilard and Fermi that the Uranium Committee had decided to limit further financial support of their research. The committee was afraid that if it funded an expensive research endeavor that flopped, Szilard’s and Fermi’s foreign backgrounds would prove a liability in case of a congressional inquiry.
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The explanation Briggs gave them was that the possibility of a costly failure loomed too large. It seemed the American government would never seriously embrace the possibility of building an atomic bomb.

CHAPTER 3

The Manhattan Project

I
F WASHINGTON FAILED
to perceive the importance of an atomic bomb early in the war, London did not. British scientists were furiously studying the feasibility of a bomb, their motivation simple and urgent: to beat Hitler to the punch. This was crucial, for by mid-June 1940 France had fallen to the Nazis. Britain now stood alone, and many people feared that Germany would soon cross the English Channel. The notion that Hitler was ahead in the atomic race had become so deep-rooted that it was treated as a certainty. “We were told day in and day out that it was our duty to catch up with the Germans,” recalled a British physicist.
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In 1940 it was still difficult for Americans to think about the war, while it was the only concern for the British.

The principles of fission and a chain reaction were clear enough to British scientists by 1940. Far less clear to them was the feasibility and expense of separating U-235 and constructing a weapon in time to be useful. Three questions overshadowed all others: How could a sufficient amount of fissionable material be collected? How much material would constitute the critical mass necessary to sustain a chain reaction? And how could the material be assembled rapidly enough so that it exploded, rather than simply fizzled like a pile of gunpowder?

The advanced state of British efforts and the desperate need to work quickly combined to effectively override whatever bureaucratic obstacles might normally have interfered with fission research. The imperative of survival concentrated British scientific minds dramatically.

Two of them, refugees Rudolf Peierls and Otto Frisch—the latter for the second time playing a decisive role—got together in early March 1940 to discuss the implications of fission. Peierls remembered: “I had a conversation with Frisch in the course of which he asked, ‘Well, Bohr and Wheeler have made it quite clear that the fission is due to 235. What would happen if one had a pure uranium 235 in a sufficient quantity? How much would you need? And if you got it, what would happen?’”
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Frisch and Peierls came up with startling answers to these questions. Early estimates of the “critical mass,” the amount of U-235 needed to start a chain reaction, had run to several tons—far too much for a deliverable weapon. But Frisch and Peierls produced an estimate that only one kilogram (just over two pounds) of U-235 could create a critical mass that would explode with a force equivalent to that of several thousand tons of dynamite. Eighty generations of neutrons would multiply in millionths of a second, yielding temperatures as hot as the interior of the sun and as deadly in radiation, before the swelling explosion separated the atoms of U-235 enough to stop the chain reaction.

“Our first reaction was to realize that this was no longer an academic exercise, but a highly practical problem, in spite of the almost science-fiction nature of large-scale isotope separation,” Peierls recalled later. “Then it struck us that, as the idea had come to us so easily, it was likely to have occurred to the Germans, and the thought of such a weapon in Nazi hands was frightening.”
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Something had to be done immediately. They decided to draw the attention of the authorities to this possibility and its implications. In a three-page memorandum, they described their calculations and a practical mechanism for a bomb: making a U-235 sphere in two parts “which are brought together when the explosion is wanted.” As soon as the hemispheres touched, the whole assembly “would explode within a second or less.” The yield would be immense. Lethal radiation would be emitted on a large scale, against which “effective protection is hardly possible.”
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