Half-Life: The Divided Life of Bruno Pontecorvo, Physicist or Spy

by Close, Frank

  At least the Americans and the Soviets were on the same side in the war. What worried him was that there were also first-class scientists in Nazi Germany, who might have similar ideas. What’s more, they also had access to large amounts of uranium and the means to enrich it. To sound the alarm, he wrote to Stalin in April 1942, urging him to call a meeting of the nation’s leading nuclear scientists.3 Flerov’s intervention was backed up by information he wasn’t aware of: the secrets obtained from Klaus Fuchs. Whether Stalin himself actually saw Flerov’s letter is unknown, but Soviet scientists were eventually alerted.

  By the spring of 1942 the Kremlin’s attitude toward nuclear research was changing. One reason for this was that the immediate German threat to Moscow had been repulsed.4 More to the point, Stalin’s henchman Lavrenti Beria, who chaired the Special Committee on the Atomic Bomb, knew from Klaus Fuchs that work was under way in the UK to separate U-235. Thus Beria knew that the British considered the challenge of the atomic bomb to have been solved in principle. Its construction would now be an engineering project.

  During 1942, the Germans regained the upper hand in their fight with the Red Army, overrunning Sevastopol and moving toward Stalingrad. This threat to the survival of the Soviet Union occupied most of Stalin’s attention, but Beria’s knowledge that a bomb was possible finally stimulated the establishment of a dedicated program in the USSR. Although the information in Flerov’s letter was probably old news, thanks to spies like Fuchs, the communication had an effect: it singled him out as an expert. In mid-July of 1942 Flerov was withdrawn from the southwestern front, summoned to Moscow, and put back into neutron research. In September, Kurchatov was brought on board. During October, while the Battle of Stalingrad was at its height, he was put in charge of the Soviet Union’s quest for an atomic bomb.

  MEANWHILE, IN THE UNITED KINGDOM, SCIENTISTS HAD BEEN investigating the practicalities of a nuclear weapon, building on the breakthrough made by Frisch and Peierls. By 1941, the British had the lead. They had investigated U-235 enrichment in experiments at Oxford, and were well advanced in the theoretical workings of a uranium bomb.

  James Chadwick, who had started the saga by discovering the neutron, was now involved both in experiments and in organizing collaboration between the various teams in the United Kingdom. This dapper, hardworking experimentalist was now showing his brilliance as an administrator of science. Like many experts, including those in the Soviet Union, Chadwick initially thought that nothing would come of this work until after the war. Then, in the spring of 1941, British scientists found that it was possible to separate the fissile U-235 from naturally occurring uranium. What’s more, the costs involved made this practical. Fuchs, who was party to this secret, duly passed the news on to the USSR. Chadwick’s reaction was also dramatic, though more personal. Upon realizing that a nuclear bomb was not only possible but inevitable, he later recalled, “I had to take sleeping pills. It was the only remedy.”5

  Chadwick wrote a report, summarizing his conclusion that an atomic weapon was feasible, and by the end of 1941 Winston Churchill gave the top-secret project the go-ahead, under the bland code name “Tube Alloys.” As before, the Soviets learned about this development from spies.6

  Tube Alloys involved many scientists and engineers, but was managed by Wallace Akers, the research director of Imperial Chemical Industries (ICI), along with the company’s senior administrator, Michael Perrin. By this point, Halban and Kowarski were in Cambridge, with the heavy water. Working with a team of physicists at Cambridge University, their goal was to create a chain reaction as a means of producing nuclear power. Although ICI was managing the enterprise on behalf of the war effort, the company saw excellent commercial possibility in the development of nuclear power, once the war was over.7

  The heavy-water project now had real urgency. German interest in heavy water hinted that they too were on the hunt for nuclear technology. Although the United Kingdom was protected from enemy occupation by the English Channel, and had survived the aerial Battle of Britain in 1940, the possibility of a Nazi invasion remained real. Separating U-235, exploiting nuclear fission, and then building a bomb would be an industrial-scale enterprise, which would be vulnerable to enemy attack if based in England. Eventually, this undertaking would be subsumed within the Manhattan Project in the United States. In 1942, to safeguard the precious heavy-water project and, we may assume, to maintain control over its commercial potential, the operation was relocated to the relative safety of Canada. Thus began the Anglo-Canadian arm of Tube Alloys, based initially in Montreal and built around the senior personnel from Halban and Kowarski’s Cambridge University team.

  Halban’s personality turned out to be a problem, both when forming the Canadian team and later when working with the Americans. He presented the group’s work on heavy water in a self-aggrandizing manner. Kowarski resented Halban’s habit of using their joint work for personal glory, and refused to go to Canada as second fiddle. So Kowarski remained in Cambridge.8 Halban, meanwhile, visited the United States in 1942 to build the team, and to discuss nuclear strategy with Enrico Fermi.

  FERMI’S PILE: 1942

  When Fermi had first started researching the possibility of a chain reaction in the United States, he had used water as moderator. Like the French, he soon realized that this was not efficient because the water tends to capture neutrons from the beam. Heavy water was scarce in the United States, so Fermi decided to try graphite instead. Graphite contains carbon, which is light and slows neutrons efficiently.

  During 1942, Fermi worked urgently to create a self-sustaining chain reaction using neutrons and uranium. To do so, he had to produce intense sources of neutrons, and assess which uranium compounds were most efficient. In addition he had to select suitable materials to moderate the neutrons—that is, to slow them to the optimal speeds that induce fission.

  From his earlier work with Pontecorvo, Fermi knew which materials worked well in small-scale tests. Now he needed to attempt the same feat on a much larger scale, appropriate to a working reactor. In Chicago research into the properties of plutonium was under way, and, because one goal of a nuclear reactor would be to produce plutonium, Chicago became the logical place for Fermi to build the first reactor prototype.

  The reactor he built there consisted of a stock of uranium oxide, in lumps about the size of tennis balls, embedded in solid blocks of graphite. The graphite blocks were stacked in a pile, which is the source for the colloquial description of this type of nuclear reactor as a “pile.” Add a source of neutrons and you have the essence of a nuclear reactor—in theory. In practice the reactor includes a lot of additional hardware, such as metals and concrete, which form the floor and general infrastructure. When the neutrons hit these materials, they are scattered or absorbed, which influences their ability to cause fission in the heart of the reactor. So to construct a working reactor Fermi would need to know how neutrons react with a whole variety of elements, in complex mixtures and ores, not just with uranium. To obtain this knowledge would require an extensive series of tests, in which compounds were irradiated with neutrons to see how much energy is lost when they scatter, or if the neutrons are absorbed. While Fermi was in the early stages of planning this strategy, Bruno Pontecorvo paid him a visit.

  Bruno had been outside this secret world for twenty months. However, although he was ignorant of the West’s growing interest in nuclear reactors, he had unwittingly become an expert in the topics that are central to their design. Indeed, by 1942, when Fermi was beginning to build the pile, Bruno knew more than Fermi himself in some areas.

  BRUNO MEETS WITH FERMI—AND HALBAN

  Toward the end of 1941 Bruno was finding it increasingly difficult to obtain radioactive materials for his work. Radium was plentiful, but supplies of less common materials seemed to have dried up, as if someone was cornering the market. The reason, of course, is that the research work that would ultimately spawn the Manhattan Project was already using up most of the available resour
ces. Bruno, a member of the general public, knew nothing of this, although he was aware that something was amiss. On November 17, 1941, he wrote a report about the shortage of radioactive sources and its effect on the development of new strategies for prospecting.9 In April 1942 Bruno met with his mentor, Enrico Fermi, in hope of getting access to more supplies.

  Fermi had spent the winter shuttling back and forth between New York and Chicago, in preparation for his reactor experiment. He too was an “enemy alien” and had to get permission every time he made the trip.10 After April, Fermi moved to Chicago permanently but was still in New York when Bruno visited him. Bruno’s colleague from Paris, Hans von Halban, and Czech physicist George Placzek were also present.

  During the get-together, Bruno told the scientists about his work on neutron well-logging, including some of the technical details. Fermi was especially interested, making suggestions, showing deep knowledge of the subject, and asking questions. Bruno, who knew nothing of Fermi’s secret project, was surprised. He assumed that his work had no obvious relevance outside the field of oil prospecting, yet Fermi showed a keen thirst for information. Of course, Fermi’s interest stemmed from the reactor project. To build a successful reactor, Fermi would have to irradiate uranium with neutrons in the presence of graphite and other materials, so it was essential for him to understand as much as possible about how neutrons behave.

  Bruno was unsuccessful in obtaining any essential materials from Fermi, but the meeting must have confirmed his suspicions that a major nuclear project was under way. Given Fermi’s questions, the presence of Halban (who had demonstrated fission alongside Bruno in 1939), and Bruno’s general knowledge of the state of nuclear physics before secrecy took over, it is inconceivable that he did not deduce what Fermi was up to. The details of the nuclear pile would have remained unknown to him, although it is clear that Fermi shared some of his own neutron data with Pontecorvo: in a report of this visit, written on April 15, Bruno commented that the data he had received from Fermi “had not been published, and cannot be published for a long time to come, because of their confidential character.”11

  Contrary to the spin propagated by the British government after Pontecorvo’s defection in 1950, it seems he was aware of at least some frontline data in 1942, several months before Fermi completed the first nuclear reactor. Moreover, Pontecorvo now knew that neutrons had become central to wartime nuclear research.

  Bruno was not alone in deducing what was going on. Others in the US had also put two and two together. Bruno’s brother, Paolo, knew Harry Lipkin, who later became a distinguished nuclear theorist but at the time was specializing in microwaves. Working together, Paolo and Lipkin were testing a receiver designed to provide early warning of planes coming over the sea, and in 1943 the pair spent two weeks together in Maine’s Acadia National Park. During this time they became friends. In Lipkin’s opinion, Paolo had concluded that the Americans were working on the atomic bomb.12 Paolo had come to this opinion because so many of Bruno’s Italian nuclear-physicist friends, including Fermi, had suddenly disappeared, and their research publications had abruptly stopped. Furthermore, the only way to contact them was to send a letter to a PO box that gave no hint of its location. It was obvious that there was a supersecret project going on, and it was clear to Paolo and Harry what it must be.

  Bruno Pontecorvo’s visit to Enrico Fermi in April 1942 would lead him too to become part of that project. It was not Fermi, however, who recruited his former pupil; Bruno joined Halban’s Anglo-Canadian team.

  THE CANADIAN CONNECTION

  In 1930, Gilbert LaBine, a Canadian mineral prospector, had discovered deposits of radium and uranium in the Northwest Territories of Canada. At that time radium was highly valued, due to its benefits in cancer treatment, but uranium was considered useless. The world supply of radium was shared between the Canadian deposits and mines in the Belgian Congo. When the war started in Europe, markets for radium shrank and the Canadian mining operation struggled to make ends meet. Everything changed with the discovery of the chain reaction and uranium’s potential as an enormous energy resource.

  In 1942 LaBine’s Eldorado Mine started to supply the US with uranium for Fermi’s reactor. The company was taken over by the Canadian government in 1943.13

  The agent for LaBine’s Canadian mine was Boris Pregel, based in New York. Pregel, who came from the Ukraine, had moved to Paris after the October Revolution in 1917, and then escaped, like Bruno, when the Nazis invaded in 1940. Upon arriving in the US, Pregel set up the Canadian Radium and Uranium Corporation of New York, which made radioactive neutron sources and luminescent signs, as well as trading in Canadian ores.14 This explains Pregel’s interest in Bruno Pontecorvo, and toward the end of 1942 Pregel began to court him. His goal was to persuade Bruno to join his New York laboratory.15

  As luck would have it, Pontecorvo was becoming increasingly frustrated at Well Surveys. His quest for radioactive materials, which were necessary for his work, was getting nowhere. He was about to accept Pregel’s offer when fate intervened in the form of three former colleagues from his Paris days: Bertrand Goldschmidt, Hans von Halban, and Pierre Auger.

  Goldschmidt (a chemist) and Auger (a physicist) were about to join Halban at the Anglo-Canadian reactor project in Montreal. Auger was to be the head of the physics division, while the head of theoretical physics would be George Placzek, who had been present when Pontecorvo visited Fermi’s laboratory earlier that year. The pivotal piece of the puzzle, Goldschmidt was to be the section leader of the chemistry division. Goldschmidt is central to our story because he had been working at Pregel’s New York laboratory, where Pontecorvo had been offered a position. In Goldschmidt’s judgment, that job was beneath Pontecorvo’s talent, and he recommended that Halban hire Bruno.

  By the time the project was operating, about one hundred scientists and engineers were involved. In building his team, Halban, protective of his patent ambitions, had been careful to keep at arm’s length anyone who might have claims of their own.16 This was one reason for Kowarski’s exclusion, and was also a bonus for Bruno. Bruno had the expertise, and had watched the heavy-water experiments in Paris, but had not been involved in the patents. Thus, as Halban knew Pontecorvo from their time in Paris, and Placzek had met him earlier that year, they arranged an interview in November 1942. On the basis of this interview, they invited Pontecorvo to join the Anglo-Canadian reactor team. The team’s goal was to design a nuclear reactor whose fundamental ingredients would be uranium and heavy water, in contrast to Fermi’s uranium-and-graphite reactor in Chicago. Ostensibly the Canadian reactor’s purpose was to provide nuclear power in the postwar era; however, it would also produce plutonium and more exotic forms of uranium, which would later have applications for atomic weapons.

  THE OPPORTUNITY TO MOVE TO CANADA CAME AT A GOOD TIME FOR Bruno, as life in the United States had begun to have some unwelcome consequences.

  Being a foreigner in the United States during the war could involve unexpected hazards. One day Bruno was driving a truck full of geophysical instruments, and made some illegal maneuver on the road. Some police officers noticed the indiscretion, and set off in pursuit. Bruno stopped, but the police became suspicious when they noticed the array of unusual instruments in the truck, covered with Bakelite knobs and dials. When Bruno started to explain the purpose of the instruments in the van, they realized he wasn’t American and exclaimed, “Enemy alien!” Bruno then attempted to retrieve his documents from his back pocket. In what he described as “like a scene from a movie,” the police, who thought he was reaching for a gun, immediately immobilized him.17 When they finally understood the nature of the situation, the police explained that he had risked being killed on the spot.

  This incident ended happily, and left Bruno with a story to add to his collection. Another experience would end less happily, however—a visit by the FBI, whose consequences are reminiscent of chaos theory, in which the flapping of a butterfly’s wings can cause a storm far a
cross the globe.

  On September 25, 1942, two FBI agents visited Bruno’s home, in view of his status as “enemy alien.”18 Bruno was away for several days at the oil fields, so the agents spoke to Marianne. At the time this seemed of little consequence except for one thing: the agents noticed “25 or 30 books or pamphlets containing Communist literature” in the house. They asked Marianne whether Bruno was a communist. She replied that she “didn’t understand and didn’t know what a communist was.” The agents noted that Marianne “spoke English well and appeared to understand all questions that had previously been asked.” According to the agents she also said that Bruno “studied under Madame Curie while he was in France,” which shows that there was a misunderstanding somewhere. Years later Bruno commented that in America he had felt an “intense anti-Sovietism” and that no one had seemed to share his “passion for the USSR.”19

  SEVEN

  THE PILE AT CHALK RIVER

  1943–1945

  WHILE BRUNO HAD BEEN OUTSIDE THE BUBBLE OF SECRECY, MUCH had happened. The events that would eventually absorb him began in 1941, when British prime minister Winston Churchill made the decision to develop nuclear weapons, under the aegis of the Tube Alloys project—which by the time Bruno joined was about to be subsumed into the Manhattan Project.

  The Manhattan Project itself included several components. At Oak Ridge, Tennessee, hundreds of acres of forest were cleared to make room for an immense gaseous diffusion plant, its purpose to separate the fissile U-235 from naturally occurring uranium. The actual design and construction of the atomic bomb occurred at Los Alamos, New Mexico. Among the nuclear physicists who moved from the UK to Los Alamos as part of Tube Alloys were Rudolf Peierls, who had first realized the bomb’s capability, and his colleague Klaus Fuchs, who was already passing information to the Soviet Union.