The Pope of Physics

by Gino Segrè

  Once the site selection meeting was over and the others had left, Compton still had to make one telephone call. That was to Fermi. Without him he knew the project could not be pursued. Fermi, the go-to physicist, Fermi, the brilliant solver of problems, Fermi, the congenial team builder, was key. Compton was also sensitive to Fermi’s general reluctance to enter into anything with political overtones.

  But a war was on. When he and Compton spoke, Fermi expressed some hesitation: it meant uprooting his family, leaving his lab, and abandoning his dedication to the purity of science. There was no doubt, however, in Fermi’s mind. He knew Mussolini and Hitler had to be defeated. It was not only his conviction in this regard, but also his identification as an American. He was grateful that the country had welcomed him and his family; he would do what was needed for America. Fermi answered Compton in the affirmative.

  25

  CHICAGO BOUND

  Fermi moved to Chicago at the end of April, but Laura stayed behind in Leonia until the end of June so that the children could finish the school year. Having to move again was hard for her husband, but it was even harder for her. After two years in Leonia, Laura was just beginning to feel settled. The American dream of a house in the suburbs and good schools for Giulio and Nella had become a reality.

  The dream continued with the acquisition of a second car. Laura, during a visit from Hans Bethe’s wife, Rose, had bought it as an essential component of suburban living. One can only imagine the car salesman dealing with two beautiful women, one with an Italian accent and the other with a German one. Little did he know they had fled respective Fascist regimes and were the wives of Nobel Prize winners, Bethe’s 1967 prize yet to come. The very capable Rose negotiated smartly, and to Laura’s delight there were unexpected dollars left over. The women had gotten such a good deal that Laura bought a new washing machine, a purchase she proudly announced to Enrico.

  As Laura had hoped, the children seemed happy in school. Fermi described them in a glowing letter on April 5, 1941, to Amaldi as “speaking with equal ease Italian and English and being hard to distinguish from the other children in the neighborhood.” As for Laura, nicknamed Lalla since childhood, he wrote, “Lalla has by now become one hundred percent American in both her habits and way of thinking.” These somewhat exaggerated observations were indicative of Enrico’s enthusiasm for his new life.

  More candidly, Laura and Enrico carried touches of the paranoia commonly felt by those labeled as enemy aliens. They burned Nella’s old second-grade reader because it was full of photographs of Mussolini. More distressing, Laura and Enrico learned from Leonia neighbors that five-year-old Giulio, apparently trying to show off, had been overheard chanting that “he wished Hitler and Mussolini would win the war.” Some severe family reprimands made sure he never said that again.

  Despite their comfortable American existence, Laura and Enrico were preoccupied with the war and its outcomes, their conversations repeatedly turning back to family and friends left behind. Stories about war horrors were reaching them. Their native country was being destroyed, physically and spiritually. After a run of Axis victories, however, Laura and Enrico felt a ray of hope in hearing that Germany’s invasion of the Soviet Union was floundering. Launched in June 1941, it had not gone according to Hitler’s plan, and the German army was stalled at the gates of Moscow, just as Napoleon’s army had been more than a hundred years earlier.

  Pearl Harbor came as a shock for the Fermis, as it did for all Americans, but they realized that the United States’ entry into the war increased the Allies’ chances of defeating Hitler and Mussolini. This made Laura happier than she otherwise might have been about moving to Chicago. She didn’t know exactly what Enrico was being called to do, but was keenly aware that he would not have agreed to the dislocation had it not been important for the war effort.

  While the children attended summer camp, Laura found a furnished house in Chicago near the university. It was available for rent because the owner was moving to Washington for war work. Before signing the lease, their landlord had to dismantle the short-wave reception of his radio set. As enemy aliens, the Fermis were not allowed to possess such a device. The owner also informed the two young tenants of the house’s third-floor apartment that they had to find lodging elsewhere. They were Japanese and the FBI had advised him that it would be inadvisable to have Italians and Japanese living in the same house.

  As an enemy alien, Fermi had restrictions placed on him. Most of them, such as not being able to have a short-wave radio, a camera, or binoculars, were minor inconveniences, but Fermi was seriously annoyed by the constraints on his travel. Fermi shuttled between Chicago and New York for the first three months after the call from Compton. He needed special permission every time he left New York, and he was unable to ask for a blanket exemption because of the project’s secrecy. Further miffed at having his Chicago mail opened before it was delivered, Fermi protested to authorities. Claiming it had been a mistake, they nevertheless continued doing so until he objected more strenuously.

  Even as Fermi was entrusted with ever more secret missions, the bureaucracies responsible for enforcing security were slow to realize his importance to the war mission. The military had performed a background check of him in August 1940. It concluded by saying, “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.” Luckily for the United States, that recommendation was not followed.

  Though Fermi was not specifically aware of the army’s background check, he would not have been ruffled to learn of it—but would have been disturbed by its vote of no confidence. Fortunately he remained oblivious of this fact and gave his all to the task at hand. Fermi actually had little trouble dealing with bureaucratic matters as long as they did not interfere with his work. He had always been willing to go along with government decrees that did not impose restrictions on his work or on the well-being of his family. This had even been true under the reign of Mussolini until circumstances changed.

  Fermi’s main objective remained fixed: to achieve a self-sustaining chain reaction. In Chicago, after seeing that changing shapes and arrangements of successive piles did not yield the anticipated improvements, Fermi became suspicious that the uranium, central to their efforts, harbored impurities just as the graphite once had. Using the idiomatic English that his assistant Anderson was teaching him, or perhaps the somewhat mangled version he was retaining, Fermi stated to his co-workers that the uranium delivered to the lab “was filthy with dirt” and that he had been “swindled by a slick sales talk.”

  At the end of July 1942, thanks to a shipment of better uranium, the ninth pile built in Chicago reached the desired goal of having k, the key neutron reproduction factor, greater than one. Two more piles were built in August to ensure everything was working properly. The stage was set for building the really big pile that would decisively show if a self-sustaining critical reaction could be obtained.

  The style of work Fermi adopted in Chicago was not one he was altogether pleased with. He liked to be the head of a small group, as at Columbia and before that in Via Panisperna, where he could be involved in every aspect of an experiment. But as head of Met Lab’s Physics Division, he had an overwhelming amount to do. He needed to direct everybody, for he was recognized as the ultimate expert on all the experiment’s facets. Fermi lamented to Segrè that his administrative role was leading him to “doing physics by the telephone.” But there was no time to waste complaining. Fermi was painfully aware that victory in the war could depend on the Laboratory’s outcomes.

  The situation at the Met Lab was complicated because all phases of the bomb-building project took place simultaneously; each challenge was linked to the others. One could not wait until k greater than one had been reached before beginning to plan for a self-sustaining critical
reaction. And one could not wait for that experiment to be completed before setting in motion plans for a much bigger pile. This pile would be called a nuclear reactor. And chemists were hard at work studying how to extract the plutonium they believed would be produced in those reactors.

  As the project grew, it came to include all sorts of scientists and even a few medical personnel. According to Laura, the only people not at the Metallurgical Laboratory were, in fact, metallurgists. Of the dozens at the lab, some were Chicago personnel switching to wartime work, while others, such as Fermi, Seaborg, Szilard, and Wigner, were recruited by Compton. They in turn brought co-workers with them. Needing to find room for all of them, Compton persuaded the mathematics department to move out of Eckhart Hall, the three-story Gothic-style building that it shared with the physics department. He then had locked doors installed to guard the Met Lab’s secrecy.

  The individuals working on the pile behind those locked doors were initially all men. That changed in August 1942 when an attractive and athletic twenty-two-year-old woman joined them. Leona Woods, born on an Illinois farm, had earned her A.B. at the University of Chicago at eighteen and was finishing her Ph.D., working in a basement office on the other side of one of those locked doors. Herbert Anderson started talking to her and realized she had technical skills the group needed. He invited her to move to the Met Lab’s side of that door. He also introduced her to his roommate, John Marshall, a young physicist working with Szilard and Fermi. She married Marshall the following year.

  Woods soon met Anderson’s boss and collaborator, Fermi. She described the impact Fermi had on her in a book written twenty-five years later. It begins, “Perhaps the most influential person in my life was Enrico Fermi, not only scientifically but also philosophically. He set the example of how best to deal with other people, how to anticipate change, how to put up with the ambient indignities and humiliations of the world and how to cope with the inevitable spiritual charges of taxes and death.” Enrico and Laura would become her close friends.

  Woods worked closely with Fermi during the war and after it. His presence was a pleasure. His qualities of “gaiety and informality … 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.” Woods’s observations echo those of all of Fermi’s colleagues.

  The company of young people, whether talking about science or indulging in athletic activities, was something Fermi greatly enjoyed. Leona Woods introduced him to swimming at Lake Michigan off the Fifty-Fifth Street breakwater near the university campus. This was regularly pursued at 5 p.m. in the summer and early fall; a few other young physicists often joined in. Harold Agnew, one of those Chicago swimming companions, described what it was like:

  I had been a varsity swimmer in high school so thought I was pretty good. But after fifteen minutes in the choppy, cold water of Lake Michigan, I was falling behind. Fermi, who swam with what I would call a “dog paddle” style, swam back to me and asked if I was OK … I barely made it to the other side of the bay and with difficulty climbed up the sea wall and sat down. Fermi said, “Meet you back where we started” and plunged back in and swam back to our starting point. I had difficulty just walking back.

  Fermi, never a stylish athlete, possessed a degree of endurance and persistence that never ceased to amaze his companions.

  Going to the Fermis’ house for dinner would often follow. There, as Woods remembered, “Laura fed us supper after supper.” The meals were relatively simple. The Fermis were not gourmets. Though he drank some wine with dinner, Fermi would add water to it first. Laura’s natural grace and refinement made the dinners elegant in their own way.

  Starting in that summer of 1942, the Met Lab had begun reorganizing. So far it had been a research project under the aegis of the OSRD; the pure research phase was about to come to an end. Full-scale efforts would need to be mounted if the United States was to commit itself to developing a bomb that made use of nuclear fission. There were two equally promising roads. One type of bomb would use plutonium and the other U-235. In both cases installations capable of extracting the materials for the bombs would need to be built. Compton was recommending and Conant was agreeing to go forward on both fronts. The three different methods being proposed for separating U-235 from U-238 should all be pursued because there was no way of knowing in advance which of them would be most effective. Though this would entail considerable expense, it might make the difference between victory and defeat in the war.

  Conant wrote to Bush on May 14, 1942, that if time not money was to be the deciding factor in achieving nuclear weapons, going forward on all fronts might require “the commitment of perhaps $500,000,000 and quite a mess of machinery.” Bush envisioned collaboration between the OSRD and the U.S. Army’s Corps of Engineers. President Roosevelt agreed; the Corps was notified and in June they selected the Boston firm of Stone & Webster as principal contractors to build a structure to house the pile. Meanwhile Compton looked for a site where the pile would be erected. It had to be close enough to the city for easy access but isolated enough for both safety and secrecy. Compton found what he was looking for twenty miles southwest of Chicago, in the Argonne Forest, so named after the final big battle of World War I.

  Concerned that the project was not being given sufficient priority, Bush wanted to accelerate necessary procurements for the pile and plans for subsequent bomb development. The response he got back from the army was that they would appoint a Corps of Engineers officer with a reputation for getting things accomplished and give him overall control of the mission.

  In September 1942 they chose Colonel Leslie Groves, deputy chief of construction for the U.S. Army, the man who had spent the previous year building the Pentagon. There was a potential issue. Groves had overcome innumerable obstacles during the Pentagon construction. He was tired of building and wanted to be posted overseas in command of troops. However, when the Corps of Engineers commanding officer told him, “If you do the job right, it will win the war,” Groves accepted. The mission’s significance was underscored when Groves was told he would be promoted to brigadier general. He decided he would not take charge of the mission until the promotion had come through, for, as he put it, “I felt there might be some problems in dealing with the many academic scientists involved in the project, and I felt that my position would be stronger if they thought of me from the beginning as a general instead of as a promoted colonel.”

  Almost everybody who worked for the controlling, demanding, politically conservative Groves described him as abrasive, harsh, and sarcastic. The terms “son of a bitch” and “bastard” run steadily through their recollections, but they all agreed he was tireless, energetic, and effective. Living up to his reputation, Groves immediately set in motion the purchase of an enormous stockpile of uranium stored in New York by Belgium’s Union Minière Company. He also laid the plan for a plant in Tennessee to separate the U-235 isotope, and convinced Delaware’s DuPont chemical company to take charge of the Chicago piles as a subcontractor to Stone & Webster.

  While this was taking place, Fermi was beginning to construct the final experimental pile, the one that would sustain a critical reaction. The number of neutrons that were produced would continue to increase unless, or until, neutron-absorbing control rods were inserted to shut it down. The moment of truth for the Met Lab was rapidly approaching.

  26

  CRITICAL PILE (CP-1)

  At this juncture, everyone at the Met Lab knew that the success of the project and perhaps the fate of the world hinged on building a large pile. Assuming the Germans were as far advanced as many thought, the scientists would have to push forward as quickly as possible. Panic that Nazis might be the sole possessors of such a weapon was leading to sleepless nights.

  The Met Lab was shrouded in secrecy. Everyone working there was voluntarily committed to self-imposed censorship. Information about CP-1, standing for Critical Pile 1, sta
yed within the confines of the lab. The security measures, later so central to building the bomb, were still nascent. Clearance for CP-1 scientists relied strongly on peer judgment, although the army was beginning to institute formal clearance measures.

  While it was understood that scientists were not to speak of what they were doing even to their spouses, Arthur Compton made an exception. As he wrote in his memoir, “I have always been one of those who must talk over important problems with his wife … I explained that if they cleared me it would be necessary for them to clear my wife as well, for it would be unrealistic to suppose that I would keep from her matters that strongly affected me.” What he previously described as an “atmosphere of mutual confidence” extended for him beyond the lab into his home. At the end of the war, when other Met Lab wives discovered this exemption, they were none too pleased.

  In spite of Laura’s scientific background and their loving relationship, the Fermis never discussed the sensitive research conducted at the Metallurgical Laboratory. While one Chicago colleague interpreted this as Laura’s “lack of interest in the physical world,” it is much more likely she intuited the secrecy of the undertaking. Laura would not have pushed Enrico to compromise that secrecy.

  In the past, Fermi had explained physics to Laura, along with anyone else willing to listen. He was an inveterate teacher. This trait was applied to laying the groundwork for CP-1 by making everyone appreciate the significance of what they were doing and to feel they were part of a team. In March, he delivered a general set of lectures about neutron physics to the Met Lab staff as a whole. He stressed CP-1’s consequential nature again in September, giving more specific talks to those working directly on the pile, explaining exactly how and why it was being assembled and how it was expected to function. Doing so was a challenge because the talks had to be technical enough to satisfy physicists and accessible enough for students helping with construction. According to Herb Anderson, the talks were “fresh, clear and convincing; they showed Fermi’s wisdom, his knowledge, his complete suitability for the job at hand.”