Life of Bruno, The Neutrino Man

Sibi K S March 17, 2016

Childhood Photo of Bruno

When I began writing this article, I was skeptical whether to present Bruno as a communist or as a scientist. Being a teacher of physics, it is apt to focus on Bruno’s life as a nuclear scientist. Bruno Pontecorvo, the nuclear physicist who disappeared at the height of cold war in 1950, needs a special mention in current scenario since Nobel prize in Physics 2015 was awarded for “the discovery of neutrino oscillations”. In common parlance, what is meant by “neutrino oscillations” is that neutrino switches back and forth between its three personalities - Electron neutrino, Muon neutrino, and Tau neutrino. To make the scientific concept digestible, I often elaborate the split personality of neutrino using the example of Vikram’s character in “Anniyan”, where he has three split personalities - Ambi, Remo and Anniyan. Bruno had made crucial contributions to many research works in Physics. To name a few, the possibility of detecting neutrinos near a nuclear reactor (Frederick Reines, Nobel Prize 1995), the unlimited source of neutrinos - The Sun (Hans Bethe, Nobel Prize 1967), detection of neutrinos using refrigeration fluid Carbon tetrachloride (Ray Davis, Nobel Prize 2002) and the curious property of oscillating between multiple identities of neutrino (Kajita & McDonald, Nobel Prize in 2015). Bruno had great insight into the nature of elusive neutrinos which was often overshadowed by his liking to communism. I believe that this may have cost him his share of Nobel Prize. Bruno was an extrovert and a brilliant scientist, on the other hand, he was also enigmatic and committed to communist dreams.

Articles related to Bruno were sparingly low compared to others who cherished using his ideas. Bruno is unique in that his life is meant to make as a biography for his scientific contributions. Bruno grew up not far from the city square where Galileo had conducted his legendary experiments with falling bodies in the seventeenth century. Bruno’s prosperous family owned a textile factory with a large number of workers, took splendid vacations in the summer, and employed private tutors to educate their children. After high school, he enrolled at the University of Pisa to pursue engineering. After completing engineering, he moved to Canada where he turned his attention to neutrinos. He was familiar with his Fermi’s theory of beta decay, which predicted the release of a neutrino along with an electron as a neutron morphed into a proton. Contrary to prevailing opinion Bruno firmly believed that physicists should be able to detect neutrinos with the right experimental setup. The odds of a particular neutrino interacting with a detector were extremely small, but Bruno thought that if there were many trillions of particles reaching a detector every second, it should be possible to capture a few. The first step toward this goal, he noted, was to identify a copious source of neutrinos. He knew that even a very large chunk of radium would not release enough neutrinos through beta decay to do the trick. But a nuclear reactor, he reasoned, should produce trillions of these particles each second. Given his intimate knowledge of nuclear power generation, this insight is not too surprising. But he went further: he outlined how to go about trapping these ghostly particles.

(a) His Research Guide, Fermi and Colleagues. (b) Bruno and his wife.

Bruno knew that, according to Fermi’s theory, two things should happen when a neutrino hits an atomic nucleus: one, the neutrino picks up a negative charge and turns into an electron, and two, the nucleus gains a positive charge to balance out the books. In other words, the atom hit by the neutrino should turn into an atom of a different element, one that is next on the periodic table, by transforming one of the neutrons in its nucleus into a proton. If this new atom was radioactive, Bruno realized, its presence would be revealed when it decays and emits radiation. So he worked out the practical requirements for setting up such an experiment. So he had to identify a target material that was relatively cheap and easy to obtain because lots of it would be needed to make a sufficiently large detector. Second, the target material had to be one that should turn into a radioactive substance upon absorbing neutrinos. Third, the radioactive product should not decay too quickly, before there was time to measure it. Based on these considerations, Bruno proposed using a huge tank of dry-cleaning fluid, or carbon tetrachloride, which contains atoms of chlorine. He knew that according to Fermi’s theory, when a chlorine atom collided with a neutrino, it should turn into argon, a radioactive element that is chemically inert. The subsequent decay of the argon atom would signal that a neutrino had struck its predecessor. He had come up with a clever way to prove the existence of the otherwise undetectable poltergeist. Yet Bruno didn’t have the chance to hunt for neutrinos himself. He applied for British citizenship and moved to England with his wife and three sons in 1948. Within two years of starting work at an atomic research laboratory in Harwell near Oxford, Bruno had some immediate concerns on his mind that eclipsed his desire to crack the case of the elusive neutrinos. Suspicions about his Communist leanings attracted growing attention from the FBI in the United States and MI5 in Britain. This pressurized for Bruno to quit his job at Harwell and disappear.

A newspaper in Italy was the first to report on their sudden disappearance under mysterious circumstances, perhaps tipped off by British investigators making inquiries in Rome. From the very beginning, the security services suspected that he had fled with his family to the Soviet Union. Indeed, some of his friends and family members were known to be leftists, if not Communist sympathizers. The newspapers at the time played with this suspicion to great effect, and a low-key scientist whom the public had not previously heard of became a worldwide sensation practically overnight. “Atom Man Flies Away” read the banner headline of the Daily Express in London, while The Manchester Guardian declared “Atomic Expert Missing.”

Even the BBC surmised that Bruno had defected behind the Iron Curtain, and reported that “British intelligence service MI5 has been brought into the hunt for the missing atomic scientist Bruno Bruno who has not been seen for about seven weeks.” News outlets around the world were keen to suggest possible motives for defection. Indeed, The Sydney Morning Herald quoted a physicist who knew Bruno, “He is one of the most all-round men in atomic science and certainly one of the very best in Britain. No doubt, a man like him would be highly useful to the Russians.” Perhaps, as many media reports pointed out, the Bruno family slipped out of Finland by train or ship from a Russian military base near Helsinki. Needless to say, the commotion surrounding Bruno’s disappearance added to the Cold War intrigue of the period.

Tomb of Bruno Pontecorvo.

In Russia, life was not easy for him. The question whether he was a scientist or a spy made him alien to Russians too. In this time, Bruno had two crucial insights that contained the keys to solving the solar neutrino puzzle. The solar neutrino problem was a major discrepancy between measurements of the numbers of neutrinos flowing through the Earth and theoretical models of the solar interior. His first insight was that there was more than one variety of neutrinos. He came to this conclusion while examining the decay of an unstable particle called a muon and tau particles. But Russians didn’t allow him to take up research in these lines since they suspected him to be a spy. What an irony! It is true that no prophet is accepted in his native land. The discrepancy in solar neutrinos has since been resolved by the new understanding of neutrino physics, requiring a modification of the Standard Model of particle physics – specifically, neutrino oscillation. Bruno's insights have helped many scientists to put forwarded following conclusion that neutrinos have mass, they can change from the type that had been expected to be produced in the Sun's interior into two types that would not be caught by the detectors in use at the time. Even though credits don’t go to him, I believe he is put aloof because he was a communist. To conclude, Bruno was a communist as well as a scientist who died without being accepted as either. The irony is very relevant to all of us who are presently involved in science. In his death bed, Bruno said, “I am not your damn spy, and I am a scientist!”

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