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

by Close, Frank

  His funeral was held on September 29. In the morning, the chandelier in the funeral parlor of the Palace of Culture at Dubna was draped in black, and as she helped prepare the flowers Irina’s “fingers were all thumbs.” Then Bruno Maximovitch’s casket was brought in. It was a grand occasion, as Dubna celebrated the life of their much-loved Academician. Mourners took turns standing beside the open casket to honor the body.48 The music of Mozart filled the room. Outside, the weather resonated with il lungo freddo, the Russian half-life of Bruno Maximovitch. “It was snowing wet snow,” Irina recalled.49 The long chill of the Russian winter had begun.

  THE FINAL IRONY

  Bruno had arguably lost his chance for a Nobel Prize when Steinberger, Schwartz, and Lederman confirmed his idea that there are distinct varieties of neutrinos. Bruno’s death now cost him a more certain share of the 2002 prize, which went to Ray Davis. By official policy, the Nobel is not awarded posthumously. Davis’s award was the climax of his forty years of experiments. His endeavors encompassed the full oeuvre of Bruno Pontecorvo, helping to convert the hypothetical neutrino into a precision tool for both physics and astronomy.

  Bruno’s idea had finally borne fruit in the quest for solar neutrinos, because the sun indeed produces neutrinos, rather than antineutrinos. Although Bruno’s original 1945 paper had dismissed the search for solar neutrinos as impractical, his paper from the following year nevertheless provided inspiration for Ray Davis. Once the existence of the particle was confirmed, Davis became the first person to look for neutrinos that had traveled from the sun. Unfortunately for Bruno, it took nearly forty years for the scientific community to accept Davis’s experiment as reliable and his results as correct. As we’ve seen, the reason it took so long was that electron-neutrinos oscillate, changing form en route from the sun—another idea proposed by Bruno Pontecorvo.

  What irony. Had there been no such thing as neutrino oscillations, Bruno would have been right once (with his advocacy of chlorine as a detector) and Davis would have observed solar neutrinos at the expected rate. The world would have applauded immediately. The irony is that Pontecorvo was right more than once. Neutrino oscillations diluted Davis’s signal to the point that people doubted his results for decades. Bruno Pontecorvo’s insight that there is more than one variety of neutrino, and his subsequent suggestion that neutrino oscillations were responsible for the shortfall in Davis’s experiments, were largely ignored. It was not until 2001 that the matter was finally settled, with the completion of the SNO experiment in Canada, so near to where Bruno’s neutrino quest had begun.50

  The most far-reaching of Bruno Pontecorvo’s ideas is surely his insight that muon-neutrinos and electron-neutrinos are different. This led to the modern Standard Model of particle physics, as well as the prediction that different varieties of neutrinos can swap identities, as long as they have some mass. This prediction, which Bruno developed over several years, reached its mature form in 1968, a full year before Davis discovered the solar neutrino anomaly.

  Perhaps it is the neutrino saga that best encapsulates the triumph and the tragedy of Pontecorvo’s scientific career. It was because of neutrino oscillations that the sun’s neutrinos were diluted before arriving in the chlorine tank. Neutrino oscillations were thus a curse. Ray Davis spent decades trying to figure out why he was seeing so few neutrinos. The explanation wasn’t confirmed until the turn of the century, leading to Davis’s Nobel Prize, which he received in 2002, at the age of eighty-seven. Bruno Pontecorvo, of course, died in 1993, unaware of the great truths he had expounded.

  He didn’t live to see the phenomenon of oscillating neutrinos established as a scientific fact. Today, this phenomenon is used to measure the subtlest properties of these ghostly particles. For some theorists, the results suggest that neutrinos may hold the answers to many of the current mysteries of the cosmos, such as why there is more matter than antimatter in the universe at large. The new science of neutrino astronomy, in which neutrinos are recorded by vast detectors under the ice of Antarctica, promises to make quantitative measurements of phenomena whose origins lie far away in the cosmos and in time.

  On two occasions, a Nobel laureate has credited Bruno Pontecorvo with the inspiration for his award. We heard Melvin Schwartz say, “His overall contribution to the field of neutrino physics was certainly major.” Ray Davis, in turn, provided this epitaph: “[Bruno Pontecorvo] opened everyone’s eyes with his original insights.”51 Like so much else in the story of Bruno Pontecorvo’s remarkable life, we can only wonder how much further these insights might have gone if he had not fled through the Iron Curtain in 1950.

  IMAGE 18.2. Bruno Pontecorvo memorial stone, Rome. (AUTHOR.)

  AFTERLIFE

  “Midway on our life’s journey, I found myself in dark woods, the right road lost.”

  —Dante’s Inferno

  NINETEEN

  THE RIGHT ROAD LOST

  MI5’S RONNIE REED HAD COMPLETED HIS INITIAL INQUIRY BY December 1950, three months after Bruno Pontecorvo’s defection. At the time, the British were oblivious to Philby’s duplicity, so no one suspected that the FBI’s interest in Pontecorvo was known in Moscow. Although the British government feared that Pontecorvo had fled because he had previously passed classified information to the Soviets, MI5 had no sure evidence, and its investigations led to no certain conclusions. However, in one assessment, at least, Reed was spot-on. In his report he concluded that Bruno was “likely to be seriously disappointed” if he had gone to the USSR in the hope of settling there peacefully.1

  After spending five years effectively confined to Dubna, and twenty more to the Eastern Bloc, Bruno finally obtained liberty only as the object of his desire—the USSR—began to fragment. Shortly before he died, Bruno admitted, “The Promised Land no longer exists; not here [in the USSR] not anywhere else.”2 He also described a recurring dream: “Sometimes during the night, I imagine there is someone in front of me saying all my scientific work is wrong. Some number, some operation was wrong at the beginning, and I worked all my life at that calculation based on that wrong data. Because of that error, all my works have been useless.” He then added, “This did not happen in physics—at least.”3 If “dreams reveal the reality which conception lags behind,” this perhaps reflects Bruno’s awareness that, in realms unrelated to science, he lost his way.4

  BRUNO PONTECORVO: SCIENTIST

  As a scientist, Bruno Pontecorvo’s name will forever be associated with neutrinos. His work on the phantom particles climaxed during the latter half of his life, and scientists today regard it as his legacy. He recognized that the weak interaction is a universal force of nature, he identified the muon as a heavy version of the electron that has its own “flavor,” and from this he deduced that there are distinct varieties of neutrinos, an idea that culminated in his theory of neutrino oscillations. Of course, some of Bruno’s 1946 neutrino report was based on the ideas of Pryce, Guéron, and Frisch, but history has credited him alone. More recently, the idea that a supernova can be observed via neutrinos has given birth to a new science—neutrino astronomy.

  Bruno was unusual in having made contributions both to theory and to experimental physics. Ugo Amaldi once asked, “How many have made great contributions in both theory and experiment? Fermi, Rutherford, Pontecorvo—not many at Nobel level.”5 Nobel laureate Jack Steinberger placed Bruno Pontecorvo high among the great physicists of the twentieth century, although he also regarded Bruno as a fantasist who in his later years sometimes claimed credit for more than his due.6

  Compare this with the opinion of Semen Gershtein, who rated Bruno as a great physicist whose career was thwarted by his move to the USSR.7 Certainly Bruno missed out on getting credit for his independent development of the idea of associated production. However, there is no evidence that he was on the right track to detecting the antineutrinos coming from reactors.

  Bruno’s early work in nuclear physics in the 1930s touches most directly on the political implications of his defection. Thi
s was the period when he made his chance observation in Rome, when he worked on isomers, when he was involved in the birth of the heavy-water fission experiments, and when he designed precision instruments for measuring radiation. The extent of his expertise and innovation in that field gives the lie to the British government’s public statements of 1950, which tried to downplay his significance by claiming he had not worked on the atomic bomb, and had no recent knowledge of nuclear secrets.8

  Contrary to this political spin, Bruno Pontecorvo had been at the center of research that was greatly relevant to the USSR’s needs. Enrico Fermi’s remark was nearer the truth when he said that Pontecorvo’s expertise would be of great general value in the USSR if he were freely admitted to the atomic project.9 The Dubna logbooks confirm Fermi’s prediction. They reveal the Soviet interest in fission and “H4 particles,” and stand as a record of the advice Pontecorvo gave upon arriving at the laboratory in November 1950. Pomeranchuk made use of Pontecorvo’s expertise in heavy-water nuclear reactors, and Bruno himself confirmed that he had given advice in this field.

  A former member of the US Atomic Energy Commission, who liaised with British intelligence in Washington around 1950, remarked, “Surely [Pontecorvo] must have revealed all after his defection but I have never seen a single piece of evidence about what he might have divulged before [1950].”10

  BRUNO MAXIMOVITCH PONTECORVO: ENIGMA

  It was once believed that the earth was at the center of the solar system. To explain the planetary orbits required a large number of “epicycles,” special refinements added to the model as better data arrived from astronomers. The theory soon became unwieldy. With the single assumption that the planets orbit the sun, however, everything suddenly fits. I take a similar view of the case of Bruno Maximovitch Pontecorvo and his possible role as a spy. One may conclude, based on the absence of evidence against him, that he had no dealings with the Soviets when he was in the West, in which case several independent theses are required to explain the various unresolved questions. On the other hand, if one accepts the hypothesis that Pontecorvo passed secrets before 1950, the kaleidoscope of facts settles into place.

  What follows is a list of kaleidoscopic facts, along with possible interpretations made on the basis of this hypothesis:

  By 1950 blueprints of the Canadian reactor were in the USSR.

  The source was someone other than Nunn May. It is possible that the Soviets convinced Pontecorvo to hand over the blueprints before his defection, to aid their goal of building a nuclear reactor for the social and economic welfare of their citizens. It would have appeared churlish if Bruno refused such a request to help an ally.

  A second sample of uranium made its way from Canada to the USSR, and Lona Cohen was its courier.

  Whereas Nunn May’s source of uranium was the American reactor, the second sample almost certainly came from Canada itself, which was only possible after the main reactor began operating in 1947. The previous year, Bruno had turned down job offers from various prestigious US universities in order to go to Harwell, and then dithered, changed the starting date, and suddenly decided to remain in Canada to work on the NRX reactor. This behavior could of course reflect genuine indecision, but it also fits rather conveniently with a portrait of a man required to keep the Soviets abreast of developments in the reactor field.11

  Lona Cohen made visits to the US-Canadian border on various occasions between 1944 and 1948, in order to exchange information with someone based in Canada. Bruno Pontecorvo likewise traveled from Montreal to the US border regularly, ostensibly to keep his application for US citizenship active.12

  If Bruno was meeting with Lona Cohen, he would have had to take precautions to protect his identity if they were seen together or, worse, if Cohen were ever arrested. We have seen evidence of Bruno’s shifty behavior during this period, turning away when forced to be in photographs at Chalk River, as if afraid to let his face become widely recognized. As the best images on a roll are generally the ones that get published, we must conclude that Bruno refused to face the camera throughout this photographic session. Bruno may simply have been in one of his childish modes, but the images at Chalk River are bizarre.

  Geoffrey Patterson sent his letter from Washington, which Philby intercepted, in July 1950, a few days before the family left England prior to Pontecorvo’s flight.

  The fact that Bruno made a precipitate decision to flee, rather than planning a more orderly move to the Soviet Union, suggests that he was reacting to a major crisis, rather than moving for personal reasons as a matter of principle. The exfiltration of the Cohens to the USSR in July 1950, only weeks before Pontecorvo’s arrival, is another intriguing coincidence.

  The Soviet reaction to his arrival, which included interrogation and five years under guard, are hardly an appropriate welcome for a hero of socialism.

  The fact that Pontecorvo chose Andropov, head of the KGB, as his contact in the Politburo, and refused to deal with anyone else, is another incident that could be quite innocent but nonetheless fits with a pattern. The Kremlin’s response is also remarkable: instead of ignoring Pontecorvo, or rejecting his request, they dispatched the same KGB officer that had guarded and helped debrief him immediately after his arrival—the person most conversant with the Pontecorvo affair. This KGB contact then had a lengthy conversation with Pontecorvo, whose details remain unknown.

  A lawyer defending Pontecorvo could argue that, as the KGB was all powerful and had helped bring him into the USSR, for whatever reasons, it was natural for Bruno to appeal to the agency for assistance. However, going to Moscow to see Andropov without an appointment would be an extremely naive move, unless Pontecorvo knew that he had considerable leverage. (Would you expect a senior member of your government to see you under such circumstances?)

  The Soviets’ treatment of Pontecorvo upon his arrival in the USSR suggested to a former head of MI5 that they didn’t trust him.13 This is perhaps understandable, whatever the reasons for his defection. However, this supposed mistrust fits uneasily with the commitment the Soviets had invested in getting him there, and Pontecorvo’s precipitate agreement to go along with the plan. The total picture fits more naturally with the idea that the Soviets were punishing Pontecorvo—that Pontecorvo had been an agent who was “trying to disengage” or become independent. He certainly wasn’t treated like a hero who had voluntarily chosen to come to the USSR in protest against Western ways.14

  ULTIMATELY, THE QUESTION OF WHETHER BRUNO PONTECORVO PASSED classified information to the Soviets before 1950 is secondary; once he was there, his know-how proved seminal for the Soviets. For all the hype about Klaus Fuchs and other atomic spies, their information soon became obsolete and was of transitory value at best. Bruno Pontecorvo, by contrast, brought with him a unique expertise, which for five years was exploited ruthlessly by the Soviet authorities to further their nuclear ambitions. Even if he passed no secrets before 1950, Bruno Pontecorvo’s later presence in the Soviet Union was potentially as significant as anything that the proven “atom spies” ever did.

  Alan Nunn May was convicted of spying in 1946, and spent seven years in British prison before being released. In 1950, Klaus Fuchs was also jailed, and was released after nine years.

  After regaining their freedom, both took up science again. Nunn May married, worked for a scientific-instrument company in England, and then became the dean of science at the University of Ghana. He retired in 1978 and returned to Cambridge, where he died in 2003, at the age of ninety-two. Klaus Fuchs returned to East Germany, where he married a friend from his student days. He had considerable success as a scientist. He won the National Prize of East Germany, and became the deputy director of the national nuclear research center in Dresden. Fuchs died in 1988, at the age of seventy-seven.

  By contrast, Bruno Pontecorvo spent forty-three years in Russia, where his scientific career was frustrated, his family was traumatized, and his ideals were slowly crushed in the face of Soviet repression. If Bruno Pontecorvo wa
s a spy, he was punished more than the others.

  OCTOBER 1992

  In October 1992, a Russian historian was doing research for a documentary about the Cold War, on behalf of the American television network ABC. A guide from the KGB press office took the researcher to a KGB hospital in Moscow, where the elderly Lona Cohen was a patient.15 She talked about the “young physicists” she had met during her time as a spy, but would not name any names. She confirmed that she went to Niagara Falls around 1945, and again in 1948 or later, “on a sightseeing pretext,” to make contact with a source from Canada.

  Next, the researcher was taken to another wing of the hospital, where they met with a man named Anatoly Yatskov. Yatskov and Pontecorvo were born just three months apart, and would die within months of each other in 1993. Yatskov confirmed that he met Pontecorvo for the first time while Pontecorvo was “on his way to the USSR.” After Bruno arrived, Yatskov served for some time as Bruno’s interpreter as well as his aide in entering Soviet life. Given their ages, and Yatskov’s experience in atomic affairs, this story is plausible and fits with the descriptions of an unnamed aide that Bruno gave to Miriam Mafai.16 A fuller biography of Yatskov would record that, in the 1940s, he had been based in New York as the controller of the Soviet atomic spy network, which included Klaus Fuchs, Ted Hall, and Lona Cohen.17 Yatskov returned to the USSR in 1947. He died of cancer in March 1993, in the same hospital where he met the researcher.

  During a conversation between the researcher and the KGB guide, the possibility of interviewing Bruno Pontecorvo came up. The KGB host duly asked Pontecorvo for an interview “just for the record,” but Pontecorvo robustly declined. The researcher did not speak to Pontecorvo personally, but his response, as related by the KGB contact, “rung in my ears”: