The Last Man Who Knew Everything

by David N. Schwartz

  In April 1942, the pile was dismantled, removed from the Schermerhorn basement, and shipped to Chicago.

  AT JUST ABOUT THE TIME COMPTON WAS MAKING THE DECISION TO bring Fermi and his team to Chicago, Fermi was having a conversation with his old friend and colleague Edward Teller.

  Teller immigrated to the United States from Europe in 1935, when he was offered a job at George Washington University in Washington, DC. He was in attendance when Fermi and Bohr explained uranium fission to the electrified audience at the March 1939 conference in Washington and then moved to Columbia in the fall of 1941 to help Fermi and the team with their graphite pile experiments. The two dined regularly at the Columbia faculty club. “Walking back to the laboratory after lunch one day,” Teller relates, “Fermi posed the question: ‘Now that we have a good prospect of developing an atomic bomb, couldn’t such an explosion be used to start something similar to the reactions in the sun?’” In what must count as one of the greatest understatements in the history of science, Teller continues, “The problem interested me.”

  The idea that the sun is powered by fusion reactions was proposed in the late 1920s by the British physicist Robert Atkinson and a German named Fritz Houtermans, later elaborated upon by the eccentric, fun-loving Russian George Gamow, and finally worked out in detail by Hans Bethe in 1938. By January 1942, physicists had a complete understanding of the basic processes underlying the way the sun and other stars work. In the hot, dense core of a star, protons are moving so fast that they break through the “Coulomb barrier”—the electromagnetic repulsion keeping two protons apart. The protons fuse, creating helium nuclei and eventually a range of other heavier nuclei. Each fusion results in radiant energy, in the form of photons and neutrinos. The physics of the process is quite complex, and Fermi’s beta decay theory helped Bethe work it out in detail. Per unit of mass, the energy released in fusion, particularly of hydrogen, is far higher than that released in uranium fission.

  Fermi’s calculations suggested that the temperatures achievable in fission weapons might well be sufficient to set off a fusion reaction in hydrogen. In sharing this idea with Teller, he unwittingly changed the course of Teller’s life. Teller became a man possessed. He realized that because hydrogen was so plentiful and so stable, a fusion weapon could have virtually unlimited destructive power, the only limit being how much hydrogen the bomb might contain. That summer Teller arrived at Berkeley to join J. Robert Oppenheimer’s team exploring the feasibility of a fast-neutron chain reaction for the bomb—the slow-neutron reactions that Fermi was studying in his pile experiments were not appropriate for the bomb itself—but Teller could think of nothing other than a fusion device. When Teller arrived in Los Alamos the following year, his obsessive work continued.

  In that fateful walk across the Columbia campus, Fermi revealed something else of great importance, although Teller does not explicitly comment upon it in his memoirs. By early 1942, even though the pile experiments had been less successful than he had hoped, Fermi had come to the conclusion that fission weapons would work. He may from time to time have expressed doubts, but from that point onward his presumption was almost certainly that fission weapons were feasible.

  THE PROCESS OF MOVING THE COLUMBIA PILE PROJECT TO CHICAGO took five months, during which time the graphite bricks and uranium slugs were sent by special shipment across country, Zinn in New York, Anderson in Chicago, and Fermi shuttling between the two. Fermi initially took up residence in Chicago at International House, an independently run Gothic-style dormitory a short walk from the center of campus. He brought two young Columbia graduate students with him, Albert Wattenberg and Bernard Feld. Wattenberg recalls playing chess frequently with Fermi during this period. Fermi could beat him in chess, but always lost in tennis. Laura stayed behind with the two children, now eleven and six, to join her husband when school let out in June.

  The University of Chicago was an extraordinary place, a center for scholarship and learning that rivaled schools far older and more prestigious. By the time Fermi arrived in mid-1942, Robert Maynard Hutchins, the enfant terrible who became president in 1929, had built a true academic powerhouse in the Hyde Park neighborhood on the south side of Chicago. The physics department was located in two adjacent buildings, Ryerson and Ekhart, almost squarely in the middle of campus. Compton gave Fermi an office in Ekhart, from which the new arrival directed activities.

  AS SOON AS THE MATERIAL ARRIVED, WORK BEGAN ON NEW PILE experiments. Joining Fermi’s team were several key individuals who became close colleagues for the rest of his life. One was an accomplished experimental physicist named Samuel Allison. A little older than Fermi, Allison spent much of the 1930s involved in X-ray scattering studies with Compton. The two wrote the standard textbook on the subject and over the years at Chicago Allison became a trusted associate of Compton. Prior to Fermi’s arrival at Chicago, Compton asked Allison to develop a reactor pile working with beryllium as a neutron moderator, and by mid-1942 he had actually achieved better results than Fermi, even though beryllium was a more dangerous substance with which to work. Allison and Fermi became close colleagues during the war and remained so afterward.

  Another colleague was a young PhD student working on a thesis under Chicago physicist Robert Mulliken. Her name was Leona Libby.* Tall, athletic, and attractive, she was the only female member of Fermi’s Chicago team. She lived with her sister near the university and early on became friendly with the Fermis. Laura would often cook meals for Leona and Herb Anderson, who took a room on the third floor of Arthur Compton’s spacious home nearby. Anderson and Libby soon discovered a mutual love of swimming and would take time off every afternoon for a dip in the freezing fresh water of Lake Michigan. Fermi, who was a passionate and exceptionally powerful swimmer fond of a peculiar dog-paddle stroke, often joined them. Harold Agnew, then a student working with Fermi at the Met Lab, recounts an outing in which Fermi challenged a group of younger colleagues to a swim from 55th Street north for about a mile. The group set off and Fermi quickly took the lead. Over his shoulder, he could see the members of the group lagging and turned back to give them encouragement, swimming in circles around them, egging them on. They finally reached their destination at 47th Street, and the group climbed ashore exhausted. Fermi gleefully announced he would swim back. His wet and weary colleagues decided to return by foot.

  Others from the Columbia team came and settled in Chicago. Szilard spent much time there and with Zinn was instrumental in pressing manufacturers to find new ways of purifying graphite and uranium. John Marshall, who joined Fermi’s team in mid-1941 and worked out the process of sintering uranium powder, also came with the Columbia team, sharing the third floor of Compton’s home with Anderson. Marshall met Leona Libby soon after arriving in Chicago and within a year they were married.

  Leona Libby was obviously charmed by Fermi. In later years she would write of this time:

  Fermi would like to show superendurance, to swim farther, to walk farther, to climb farther with less fatigue, and he usually could. In the same way he liked to win at throwing the jackknife, pitching pennies, or playing tennis, and he usually did. These qualities of gaiety and informality of his character made it easy for the young members of the laboratory to become acquainted with him. He was an amazingly comfortable companion, rarely impatient, usually calm and mildly amused.

  It was a heady experience for her, for Marshall, and for the other young members of the Met Lab. Already a legend among physicists for his work in Europe, already the subject of growing mythology, here was Enrico Fermi in the flesh, and they found him to be unassuming, approachable, informal, and fun. He had a healthy respect for his own abilities, but that was based on an empirical fact—he was just that much better a physicist than anyone else. Fermi had an enormous personal impact on his colleagues, with whom he collaborated and also went swimming and hiking. They would remember these days for the rest of their lives.

  For those first few months in Chicago, Fermi enjoyed working w
ith his new young colleagues and was reminded of the early Rome years. He was no longer working under the cloud of fascism, and his eager, positive new colleagues enjoyed his infectious sense of fun, a sense that had been entirely absent in the final years in Rome. He would stay close to these colleagues for the rest of his life.

  Over the course of 1942, however, many others joined the Met Lab, working under Compton’s watchful, forceful leadership. Perhaps most important, the Princeton team—Wigner and Wheeler, in particular—arrived in Chicago soon after Fermi. They delved deep into the theory of the pile and were instrumental in the further development of the pile concept at later stages of the Manhattan Project. In the end, some forty physicists were in Chicago working in secret to create the world’s first controlled uranium chain reaction. As Compton grew increasingly confident in Fermi’s abilities, he put Fermi in charge of ever more elements of the project, until Fermi complained privately to Segrè that he felt like he was doing physics “by phone,” perhaps referring to the dramatic increase in his administrative responsibilities, which took him away from the lab and pure physics. Fermi disagreed with some of the directives the team received from project leaders in Washington. Szilard recalls that Fermi once complained, in frustration, “If we brought the bomb to them ready made on a silver platter, there would still be a fifty-fifty chance that they would mess it up.” He sometimes felt that he was a cog—an important cog, but a cog nevertheless—in an increasingly large and unwieldy machine.

  NUCLEAR REACTORS TODAY ARE MAJOR ENGINEERING PROJECTS involving careful planning and reams of design drawings, all carefully vetted and reviewed at every step. In contrast, the first operational nuclear reactor was planned in Fermi’s head, based not on extensive engineering drawings but on his sense of how the neutron flow would develop within the heart of the pile and make its way from one uranium slug to the next. He gave general instructions to machinists and his fellow physicists and let them do the rest. He did not have access to computers to calculate what the geometry of the lattice should be, how big the pile would have to be before it went critical, or how hot it might get as it ran. All these calculations were done either in his head or on his ever-ready slide rule, with the more junior physicists at his side providing back up. By the time work actually began on the final Chicago pile in November 1942, Fermi and his team had built twenty-nine experimental piles testing various aspects of material and configuration. These experiments gave Fermi an intuitive sense of how the pile should be constructed and led to the apparatus that took shape in the squash court under the stands at the abandoned Chicago football stadium.

  In later years, Fermi told his wife that the overall structure of the pile came to him in May 1942 while walking with colleagues along the Indiana dunes on Lake Michigan’s southern shore. Like the previous piles, it would be modular, constructed of bricks of graphite embedded with uranium and interspersed with bricks of pure graphite. It was basically quite simple. Modern reactors, built with cooling mechanisms, multiple redundant safety mechanisms, elaborate diagnostics and designed to produce electricity, are highly complex. Fermi’s piles were brutally simple, with only two objectives in mind. One was the proof of concept—a controlled, self-sustaining nuclear fission chain reaction. The other was to serve as a machine to produce plutonium.

  If natural uranium is exposed to neutron bombardment, the U-238 in the uranium sometimes undergoes a series of transformations through beta decay into a new element, plutonium 239 (Pu-239). Studying Pu-239, physicists concluded that it might also be used as a material for weapons.

  In 1940, a UC Berkeley team led by chemist Glenn Seaborg produced a small amount of this new element by bombarding natural uranium in the Berkeley cyclotron. This process by its very nature could produce only minute quantities of the new element, nowhere near enough for a weapon, but enough to study its properties. Experiments at Berkeley subsequently demonstrated that, as theory predicted, it would be a suitable alternative to U-235 for a fission weapon. It might also prove easier to produce in substantial quantities than U-235. If Fermi’s exponential pile could be made to work, perhaps it could be scaled up to become a plutonium factory. Traditional chemistry could be used to separate Pu-239 from reactor by-products. Hence the priority placed on plutonium research.

  So the project Fermi undertook to complete when he arrived in Chicago had two distinct purposes. The creation of a self-sustaining fission chain reaction was clearly important to demonstrate the chain reaction concept. If one could be created, then in principle uranium fission weapons could be built, although enormous challenges would remain. It would also create the possibility of plutonium production, providing a second possible route to a fission weapon. At this particular juncture the success of the Manhattan Project depended almost entirely on Fermi’s ability to achieve a self-sustaining reaction. If he felt any pressure at all, he did not show it, perhaps because by this time he felt certain he could make it work.

  LAURA ARRIVED WITH THE CHILDREN IN SEPTEMBER 1942 AND they moved into a grand, old, three-story house at 5537 South Woodlawn that had been vacated by its owner, investment manager Sydney Stein Jr., who moved to Washington to help in the war effort at the Bureau of the Budget. As enemy aliens, the Fermis were not allowed to keep the large floor-standing radio that came with the living room furnishings. After consulting with the FBI, the landlord removed it. On the third floor lived two Japanese exchange students, stranded in Chicago when the war broke out. With an Italian family occupying the rest of the house, the landlord decided—presumably also in consultation with the FBI—to evict the students.

  The Fermis soon began to entertain at the house on a regular basis. With new physicists arriving in Chicago almost daily, Laura believed that she could help out, in spite of all the secrecy surrounding her husband’s work, by providing an active social life for the newcomers. Libby recalls attending parties with some of the most distinguished scientists of the day, watching as Enrico led the group in some of his favorite parlor games from his Rome days—games he was always determined to win. These frequent parties forged social bonds within the team and gave wives who were not privy to their husbands’ actual work a sense that they were doing something useful for the war effort. The bonds forged in Chicago and cemented during the later period at Los Alamos were to last for decades.

  THE IDEA THAT BEGAN TO FORM ON THE INDIANA DUNES WAS different from the idea that drove the geometry of previous piles. The Columbia piles were squared-off towers of graphite and uranium, rising as high as the Schermerhorn ceiling permitted. Now he began to play with another shape: a flattened, roughly spherical, ellipsoid shape. It was clear to Fermi that such a shape allowed for neutron diffusion that would be more optimal for the reproduction factor. Surface area was Fermi’s enemy, because as neutrons escaped from the pile through the surface contact with the air they were lost from future fissions. A cube of a given volume has a greater surface area than a sphere of the same volume. The smaller the surface area for a given volume, the more likely it would be for neutrons to stay inside the pile. Thus, a spherical shape was better than a squared-off shape. Before he could begin to build anything, however, the Chicago team would have to solve two major problems. One of them involved the purity of materials for the new pile. The other was to figure out how to make a spherical shape sit stably on the floor.

  The more he thought about it and the more he discussed the matter with Szilard, Wigner, Allison, Wheeler, and others, it was clear that purity of the materials used in constructing the pile would be a central issue. Impurities could absorb neutrons in unpredictable ways, slowing the process and constraining the reproduction factor. Even if they did not absorb neutrons themselves, under neutron bombardment they might transform into new isotopes that would be neutron absorbers. Szilard and Zinn continued working with producers of graphite and uranium to get materials of sufficient purity to increase the reproduction rate to an acceptable level. Throughout the summer and fall, Fermi and the team built one small experimental
pile after another, testing newly arrived materials: new graphite, better quality uranium oxide powder, and uranium metal, cast into egg-shaped lumps by a team at the University of Iowa. Fermi began to sense how the different materials reacted, how different lattice structures produced different intensities of neutrons, how the reproduction factor varied with material and configuration. These experiments continued during the late summer and early fall of 1942.

  The ellipsoid shape created a problem of its own: how to build it so that it would be absolutely stable on the floor of the lab. The pile would grow layer by layer from the ground up, with the bottom layer laid out in a rough circle. It would gradually grow wider until it reached a certain height above the floor and then begin to reverse its growth symmetrically. From the side it would look like a flattened sphere. How would all these bricks be held in place? The solution was to create a wooden frame that would, they hoped, hold the layers stable as the pile rose from the lab floor. It required strength and stability, because the pile would be quite heavy and the team could ill afford an accident involving the pile sliding into a messy mountain of uranium and graphite on the lab floor. Fermi found a master carpenter employed by the university who was up to the task.