Bruno Pontecorvo (; , Bruno Maksimovich Pontecorvo; 22 August 1913 – 24 September 1993) was an Italian–Russian nuclear physicist, an early assistant of Enrico Fermi and the author of numerous studies in high energy physics, especially on neutrinos. A convinced communist, he defected to the Soviet Union in 1950, where he continued his research on the decay of the muon and on neutrinos. The prestigious Pontecorvo Prize was instituted in his memory in 1995.
The fourth of eight children of a wealthy Jewish-Italian family, Pontecorvo studied physics at the Sapienza University, under Fermi, becoming the youngest of his Via Panisperna boys. In 1934 he participated in Fermi's famous experiment showing the properties of slow neutrons that led the way to the discovery of nuclear fission. He moved to Paris in 1936, where he conducted research under Irène and Frédéric Joliot-Curie. Influenced by his cousin, Emilio Sereni, he joined the Italian Communist Party, whose leaders were in Paris as refugees, and as did his sisters Giuliana and Laura and brother Gillo. The Italian Fascist regime's 1938 racial laws against Jews caused his family members to leave Italy for Britain, France and the United States.
When the German Army closed in on Paris during the Second World War, Pontecorvo, his brother Gillo, cousin Emilio Sereni and Salvador Luria fled the city on bicycles. He eventually made his way to Tulsa, Oklahoma, where he applied his knowledge of nuclear physics to prospecting for oil and minerals. In 1943, he joined the British Tube Alloys team at the Montreal Laboratory in Canada. This became part of the Manhattan Project to develop the first atomic bombs. At Chalk River Laboratories, he worked on the design of the nuclear reactor ZEEP, the first reactor outside of the United States, which went critical in 1945, followed by the NRX reactor in 1947. He also looked into cosmic rays, the decay of muons, and what would become his speciality, neutrinos. He moved to Britain in 1949, where he worked for the Atomic Energy Research Establishment at Harwell.
After his defection to the Soviet Union in 1950, he worked at the Joint Institute for Nuclear Research (JINR) in Dubna. He had proposed using chlorine to detect neutrinos. In a 1959 paper, he argued that the electron neutrino () and the muon neutrino () were different particles. Solar neutrinos were detected by the Homestake experiment, but only between one third and one half of the predicted number were found. In response to this solar neutrino problem, he proposed a phenomenon known as neutrino oscillation, whereby electron neutrinos became muon neutrinos. The existence of the oscillations was finally established by the Super-Kamiokande experiment in 1998. He also predicted in 1958 that supernovae would produce intense bursts of neutrinos, which was confirmed in 1987 when Supernova SN1987A was detected by neutrino detectors.
Biography Early life and education
Pontecorvo was born on 22 August 1913 in Marina di Pisa, the fourth of eight children of Massimo Pontecorvo and his wife Maria . His older brother Guido, who was born in 1907, became a geneticist. Another older brother, Paolo, who was born in 1909, became an engineer who worked on radar during World War II. His older sister Giuliana was born in 1911. His younger brother Gillo was born in 1919, and is best known as the director of The Battle of Algiers. He also had two younger sisters: Laura, who was born in 1921, and Anna, who was born in 1924, and a younger brother, Giovanni, who was born in 1926. His family was wealthy; Massimo owned three textile factories employing over 1,000 people. The family was Jewish and non-observant,Simone Turchetti. The Pontecorvo Affair: A Cold War Defection and Nuclear Physics (pp. 15—16)Miriam Mafai. Il lungo freddo from Rome on his father's side and from Mantua - on his mother's. His grandfather on the maternal side, Arrigo Maroni (1852–1924), born in Mantua, was director of the Fatebenefratelli Hospital in Milan;Necrologio Arrigo Maroni (L'università italiana rivista dell'istruzione superiore) his mother's cousin was a notable zoologist, Elisa Gurrieri-Norsa (1868–1939).Adele Maroni (necrologio, L'università italiana rivista dell'istruzione superiore)Mario Avagliano, Marco Palmieri. Di pura razza italiana
He entered the University of Pisa intending to study engineering, but after two years, he decided to switch to physics in 1931. On the advice of his brother Guido, he decided to study at the University of Rome La Sapienza, where Enrico Fermi had gathered together a group of promising young scientists known as the Via Panisperna boys after the name of the street where the Institute of Physics of Rome University was then situated. At the age of 18, he was admitted to the third year of Physics. Fermi described Pontecorvo as "scientifically one of the brightest men with whom I have come in contact in my scientific career". As their youngest member, the group nicknamed him Cucciolo, which means "puppy".
In 1934, Pontecorvo contributed to Fermi's famous experiment showing the properties of slow neutrons that led the way to the discovery of nuclear fission. Pontecorvo's name was included on the Via Panisperna boys' patent "To increase the production of artificial radioactivity with neutron bombardment". He was made a temporary assistant at the Royal Institute of Physics on 1 November 1934 and the University of Rome, and on 7 November, he was listed as co-author, along with Fermi and Rasetti, of a landmark paper on slow neutrons that reported that hydrogen slowed neutrons more than heavy elements, and that slow neutrons were more easily absorbed. An Italian patent was granted for the process in October 1935, in the name of Fermi, Pontecorvo, Edoardo Amaldi, Franco Rasetti and Emilio Segrè. A US patent was granted on 2 July 1940.. The US patent was .
Early career In February 1936, Pontecorvo left Italy and moved to Paris to work in the laboratory of Irène and Frédéric Joliot-Curie at the Collège de France on a one-year scholarship to study the effects of collisions of neutrons with protons and on the electromagnetic transitions among isomers. During this period, influenced by his cousin, Emilio Sereni, he adopted the ideals of communism to which he remained loyal for the rest of his life. He formed a relationship with Helene Marianne Nordblom, a Swedish woman working in Paris as a nanny. Whether because of his relationship with Marianne, his interesting work on isomers, or the deteriorating political situation in Italy, he turned down an opportunity in 1937 to apply for a tenured position at the University of Rome to stay in Paris.
Marianne moved in with Pontecorvo at the Hôtel des Grands Hommes on the Place du Panthéon on 4 January 1938. Their son, Gil, was born on 30 July. Her visa expired, and she had to return to Sweden in September. Pontecorvo accompanied her, leaving Gil behind in a residential nursery in Paris. Travelling back to Paris alone, he dined with Manne Siegbahn and met with Niels Bohr and Lise Meitner on 12 October 1938. Pontecorvo was now unable to return to Italy because of the Fascist regime's racial laws against the Jews. This caused the breakup of the Via Panisperna boys, with Fermi moving to the United States. Pontecorvo's family also dispersed. Guido moved to Britain in 1938, followed by Giovanni, Laura and Anna in 1939, while Gillo joined Pontecorvo in Paris.
Working in collaboration with the French physicist André Lazard at Joliot-Curie's laboratory at Ivry-sur-Seine, Pontecorvo discovered what Frédéric Joliot-Curie called "nuclear phosphorescence"; the emission of X-rays when neutrons and protons were excited and returned to their ground state. He also discovered that some isomers do not change into other elements on decaying radioactively. This expanded the scope for their use in medical applications. For this ground-breaking research, Pontecorvo received a Curie-Carnegie scholarship and funding for his work from the French National Centre for Scientific Research.
Second World War
Escape from France In June 1939, Pontecorvo applied for a visa to visit Sweden, but his application was rejected. On 23 August came the news of the Molotov–Ribbentrop Pact. He joined the French Communist Party the next day as an affirmation of his personal faith in the Soviet Union. Marianne rejoined him in Paris on 6 September 1939, three days after the British and French declaration of war on Germany in response to the German invasion of Poland that started the Second World War in Europe. They were married on 9 January 1940.
As the Germans closed in on the city in May 1940, they decided to leave. Although the British offered refuge to French nuclear scientists, including Hans von Halban and Lew Kowarski, they regarded Pontecorvo as an "undesirable". Fortunately, Segrè had been given an offer of employment in Tulsa, Oklahoma, by two European expatriates who were looking for an expert on neutron physics. Segrè had turned down the offer — he already had a good job at the University of California — but recommended Pontecorvo.
On 2 June 1940, he saw Marianne and Gil off with their chattels on a train to Toulouse, where his sister Giuliana lived with her husband, Duccio Tabet. On 13 June, just a day before the Germans entered Paris, Pontecorvo, his brother Gillo, cousin Emilio Sereni and Salvador Luria set out for Toulouse on bicycles. It took them ten days to reach Toulouse. Luria went to Marseilles, from whence he eventually made his way to the United States. Pontecorvo, Marianne, Gil, Giuliana and Tabet boarded a train that took them to Lisbon via Madrid on 19 July 1940. Both women were pregnant. Marianne had a miscarriage and was hardly fit to travel, but nonetheless boarded the liner Quanza on 9 August 1940 on its voyage bringing refugees to the United States. Both women were seasick. On 19 August 1940, the ship reached New York City, where they stayed with his brother Paolo. While there, he visited Fermi at his new home in Leonia, New Jersey.
Prospecting in Oklahoma In Tulsa, Pontecorvo went to work for two European migrants, Jakov "Jake" Neufeld and Serge Alexandrovich Scherbatskoy, who had founded a company called Well Surveys with funds provided by Standard Oil. Their idea was to apply nuclear physics to searching for minerals. A gamma ray device had been successful at analysing rock outcroppings. Inspired by the work done in Italy and France, they reasoned that neutrons, being without electrical charge, might be able to detect different elements beneath the surface by inducing radioactivity on the rocks. In Pontecorvo, they had the expert they needed.
Pontecorvo created a neutron source using radium and beryllium, as the Via Panisperna boys had, with paraffin wax as a neutron moderator, and measured the absorption of different minerals using methods developed by Fermi and Amaldi. By June 1941, he had a device that could differentiate shale, limestone and sandstone, and map the transitions between them. The technique may be considered the first practical application of the discovery of slow neutrons, and would still be in use decades later for well logging. He filed four patents relating to his instrumentation.. The patents were: , , and .
By late 1941, Pontecorvo was having difficulty securing the radioisotopes that he needed. Unbeknown to him, the Manhattan Project, the wartime effort to build atomic bombs, was cornering the market. In an attempt to obtain them, he met with Fermi, von Halban and George Placzek in New York in April 1942. He was unable to secure the supplies he wanted, but Fermi showed an unexpected keen interest in the Wells Surveys work.
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