Authors: Brian Van DeMark
Bethe’s first meeting with Robert Oppenheimer had not gone so well. Oppenheimer had cuttingly dismissed a paper that Bethe presented at a conference in Germany in 1929. They remained in touch, however, and Bethe began to perceive depths of intellect and culture in Oppenheimer that he had not noticed at first. At a physics meeting in Seattle in the summer of 1940, Oppenheimer gave what Bethe considered a “beautifully eloquent speech” about the danger that Nazism posed to Western civilization. Afterward, Bethe and Oppenheimer talked passionately about the threat posed by Hitler.
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After the fall of France, Bethe decided to help the West’s defense efforts by studying the penetration of armor plate by artillery shells. His paper on the subject was so valuable that the army promptly classified it and gave him a security clearance. He was then asked to help with radar, the most important science project of the war up to that time. In May 1942 he moved from Cornell to MIT, where work on radar was being conducted in the greatest secrecy. Bethe was at MIT when Oppenheimer asked him to come to Berkeley and work on the bomb. He initially turned Oppenheimer down, thinking the project was an “improbable boondoggle.”
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If a physicist wanted to help win the war, he thought, he should stick to something practical like radar. But after much arm-twisting by Oppenheimer, he accepted the invitation to Berkeley. In the end, strong feelings about the Nazis and scientific curiosity persuaded him. “The fission bomb had to be done,” he later said, “because the Germans were presumably doing it.”
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On the way to Berkeley, Bethe stopped for two days in Chicago, where Teller briefed him in detail on the work of the Met Lab. Bethe learned for the first time of Fermi’s work on the pile, of plans for plutonium production, and of U-235 isotope separation. Though Lawrence’s uranium-separation strategy struck him as an unbelievably expensive method using brute force, Bethe was greatly impressed by the talent and creativity with which Fermi was working on a chain reaction. Teller continued the trip west with him, and they joined Oppenheimer and a few other physicists in Berkeley in early July.
The purpose of the Berkeley conference was to determine whether an atomic bomb could actually be made. There were many questions to be answered: How many neutrons were released with each fission of a uranium nucleus? How did neutrons from one fission produce a secondary fission when they hit another uranium nucleus? Were there other fissionable materials besides uranium, with higher yield? How was fissionable material assembled fast enough to produce an explosion? What happened during the explosion? How could the explosive power be maximized? It was a demanding list.
The conferees met throughout July 1942 in Oppenheimer’s office on the third floor of LeConte Hall. Oppenheimer’s office had French doors opening onto a balcony with a magnificent view looking down the eucalyptus-covered Berkeley hills, across San Francisco Bay to the Golden Gate. The conferees met under what, for those days, were considered strict security arrangements. The windows were covered in wire mesh, including the exit to the balcony, and the door was fitted with a special lock with a single key that was given to Oppenheimer. Most of Berkeley’s students were away on vacation or military service that first summer of the war, and the physicists had practically the whole campus to themselves.
Each scientist played his role. Oppenheimer posed penetrating questions. Teller threw off ideas like sparks. Bethe subjected them all to exhaustive scrutiny. They sifted through report after report, filling the blackboards in Oppenheimer’s office and LeConte Hall classrooms with calculations and diagrams. They had been thinking about the key problems, they knew the general picture, but they had not yet pulled together all the pieces of the puzzle. Now they did. “We are up to our ears in every kind of work,” Oppenheimer reported to another physicist during the conference.
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Among many things they discussed was a far-fetched idea that Teller had hatched with Fermi the year before: could the explosion of an atomic bomb heat the nuclei of heavy hydrogen (deuterium) enough to begin thermonuclear fusion? Such a bomb would be infinitely more destructive than even a fission bomb. Out of curiosity, Oppenheimer vigorously pursued the idea of a “superbomb” based on thermonuclear fusion. He and the other conferees made extensive calculations, which were disappointing—such a weapon apparently could not be made. Yet the concept of a “superbomb” would remain a nagging challenge to Teller’s restless mind, one that he took secretly to heart and would nurse for years to come.
The Berkeley conference was the first and only time Oppenheimer and Teller discussed physics with the shared purpose that they enjoyed with other colleagues throughout their lives. “We had a few days of quite violent discussion by which we even learned something,” Teller reported to Fermi at the end of their deliberations.
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Teller attributed the progress they had made to Oppenheimer. It was a pleasant surprise for Teller, who had first glimpsed Oppenheimer four years earlier at a physics colloquium in Berkeley. After the colloquium Oppenheimer had taken Teller to dinner at a Mexican restaurant in San Francisco. Teller had found the dishes spicy and Oppenheimer overwhelming, even intimidating.
Now, during the summer conference, Oppenheimer and his wife, Kitty, invited Teller and his wife, Mici, to dinner at their home on Eagle Hill. The other guests at dinner that night were Haakon Chevalier and his wife, Barbara. Teller brought along a record of his favorite Mozart piano concerto as a hospitality gift, which he felt Oppenheimer found uninteresting. His feeling was subtly reinforced by
mikosh
, a cultural inferiority complex that Teller, a Hungarian Jew, felt toward Oppenheimer, a descendant of German Jews. Teller had imagined or actually experienced this superior feeling of Germans toward Hungarians as a graduate student at Leipzig and Göttingen and was sensitive—perhaps hypersensitive—to it. Oppenheimer may have been born in New York, but to Teller he represented the Germany that had always been out of reach, even to the son of a respected and socially responsible Hungarian lawyer. That they were both Jews made little difference, since in Oppenheimer Teller saw a Jewish elite far above his orbit, an elite whose riches and status commanded respect and opened doors. Oppenheimer, unlike Teller, did not hail from the trembling class.
Feeding the electricity between Oppenheimer and Teller were their differing personalities and temperaments. Teller was gregarious and extroverted, Oppenheimer was shy and introverted. However, both were arrogant, ambitious, charismatic, and intense. Both wanted to be “top dog” and resented those whom they thought were rivals. Running through their relationship from the beginning was an unstated but unmistakable—and inescapable—tension. Their fates were intertwined, although each barely sensed it at the time.
At the end of the Berkeley conference, Oppenheimer, Teller, and Bethe concluded that an atomic bomb
could
be made, but it would require an immense scientific and engineering effort. They now realized the sheer scale and complexity of what was involved, and how much of themselves would be required to make the bomb a reality.
The design and construction of the bomb would be a major task, but until enough plutonium could be produced, bomb design was of secondary importance. The task of constructing a chain-reacting pile that would yield plutonium fell to Fermi, with help from Szilard. One of the biggest problems was the impurity of uranium and graphite supplies. Szilard immediately set about convincing the main U.S. graphite producer, Union Carbon and Carbide, to produce very large quantities of incredibly pure graphite. He also had Compton call Westinghouse and ask, “How soon can Westinghouse supply three tons of pure uranium?” Compton heard a gagging sound at the other end of the line, but the firm’s response was positive. Using uranium ore spirited out of the Belgian Congo at the time of the fall of France and sent to a warehouse in New York, Westinghouse stepped up purification from eight ounces a day to over five hundred pounds, and by November 1942 had delivered the three tons.
Fermi worked countless hours with younger scientists planning the pile and calculating the uranium and graphite needed. He was not above doing tedious work himself. “Fermi was doing it with all the rest of us,” said a young physicist who helped construct the pile. “When he was on shift, he was on shift—the same as the rest of us.”
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It made him a beloved figure. He found release from the strain and long hours of work by swimming on hot summer afternoons in the choppy waters of Lake Michigan off the huge breakwater rocks from the Fifty-fifth Street Promontory to the Sixty-eighth Street Pier. He did a funny dog paddle but had amazing stamina.
The site of the pile’s construction was a large squash court beneath the west stands of Stagg Field, whose masonry facade and crenellated towers facing Ellis Avenue between East Fifty-sixth and Fifty-seventh Streets a block north of Eckart Hall concealed a warren of indoor courts and locker rooms. Scarcely anyone had come this way since the university abandoned participation in intercollegiate football several years before. But here, on November 7, 1942, assembly of the world’s first nuclear reactor—called Chicago Pile One (CP-1)—began. There was nothing ceremonial about it. A couple of physicists finished sweeping the floor of a square-shaped gray rubber balloon that would enclose the pile. The huge balloon was hung from the ceiling, with one side left open; then, in the center of the floor, a layer of graphite bricks was placed in a circle and braced by a wooden frame. Somebody jokingly shouted, “Well, Enrico, why don’t you lay the cornerstone?”
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Fermi grabbed a graphite brick and placed it with a grin.
The concept was to build a lattice of graphite bricks, interspersing plugs of uranium oxide until it was big enough to maintain a critical reaction. There were no plans or blueprints, just layer after layer of dark, slippery graphite bricks four inches wide and deep and sixteen inches long and uranium plugs weighing six pounds each and spaced eight inches apart. A layer of solid graphite blocks alternated with a layer of graphite blocks filled with uranium plugs. The pile had an odd shape. The base was square like a windowless brick house, but the top was tapered in the form of a roughly flattened sphere. Before the work was finished, 45,000 graphite bricks with uranium plugs were stacked into a sphere twenty-five feet wide at its midpoint and twenty feet high enclosed within the square rubber balloon.
Fermi directed assembly of the pile from his office in Eckart Hall and then from the balcony of the squash court as the work progressed. Young physicists laying graphite bricks carefully lined up slots for control-rod channels of neutron-absorbing cadmium that passed at various points through the pile. As it grew, layer by dusty layer, they assembled wooden scaffolding to stand on and ran loads of bricks up to the working surface on a portable elevator. “It was hard work, and it was dirty,” said one who helped build the pile. “You’d look like you came out of a Kentucky coal mine at the end of a shift.”
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Fine black powder covered faces, lab coats, shirts, trousers, walls, flooring—everything. A dark haze dispersed light in the floodlit air. The only white to be seen was the gleam of teeth. “The people were all black with red eyes peering out,” recalled an eyewitness. “It was like a scene from hell. It was a different world.”
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As the pile neared completion, Compton had to decide whether to bring the pile to critical mass (initiating a self-sustaining chain reaction) right in the middle of a crowded city. “We did not see how a true nuclear explosion, such as that of an atomic bomb, could possibly occur,” Compton later wrote with more calm and certainty than he probably felt at the time. “But the amount of potentially radioactive material present in the pile would be enormous and anything that would cause excessive radiation in such a location would be intolerable.”
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He asked Fermi about the probability of controlling a chain reaction; Fermi said it could be controlled.
Compton gave Fermi permission to go ahead, but he chose not to inform University of Chicago president Robert Maynard Hutchins. “The only answer he could have given would have been—no. And this answer would have been wrong. So I assumed the responsibility myself.”
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If the number of neutrons generated became too large, the pile would heat up and melt down. No one, including Fermi, could be sure that a meltdown would not occur and take all Chicago, or even Illinois, with it, so two young physicists volunteered to form a “suicide squad.” The two would stand on scaffolding overlooking the pile with buckets of liquid cadmium in their grip. If all other controls failed and the pile started to melt down, they would hurl the cadmium on it.
As the pile grew larger, the neutron strength became stronger, so it became easier to predict when it could be made to go critical. When the fifty-seventh layer of bricks was completed on the night of December first, the work was halted. All the control rods but one were removed and the neutron count was taken. It was clear from the count that once the remaining rod was removed, the pile would go critical. Since it was late, the control rods were put back in and locked up for the night. The pile contained 771,000 pounds of graphite and 12,400 pounds of uranium, assembled at the cost of $1.5 million. Fermi was confident that the next day’s experiment would be a success: he would start—and control—a chain reaction. And if he could not? asked one of his colleagues. “I will walk away—leisurely,” he breezily answered.
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