Emilio Segr? The Nobel Prize in Physics

biography

Emilio Segr? is credited as the co-discoverer of three chemical elements, technetium in 1937, astatine in 1940, and plutonium in 1941. In addition, he was codiscoverer, with his former student Owen Chamberlain, of the antiproton in 1955, an achievement for which he shared the 1959 Nobel Prize in physics. Segr?'s early academic career is closely intertwined with that of nuclear physicist Enrico Fermi , under whom he received his doctorate at the University of Rome in 1928. Segr? then continued his affiliation with that university for most of the next eight years. In 1936, he was appointed professor of physics at the University of Palermo, but was discharged two years later by the Fascist government of Benito Mussolini. Already in the United States at the time of his dismissal, Segr? accepted an appointment at the University of California at Berkeley, where he remained until his retirement in 1972. He returned to the University of Rome, where a special chair in physics had been created for him by the Italian government. Emilio Gino Segr? was born on February 1, 1905 in Tivoli, Italy, one of three sons born to Giuseppe Segr?, a manufacturer, and the former Amelia Treves. Segr? attended the local elementary school in Tivoli and graduated in 1922 from the Liceo Mamiani in Rome. He subsequently entered the University of Rome, where he majored in engineering. Segr? eventually switched to physics, however, and completed his Ph.D. in that field in 1928. Biographers have conjectured that Segr?'s decision to change majors was strongly influenced by his mentor, Enrico Fermi, on the Rome faculty. In any case, Segr? was Fermi's first doctoral student at Rome.

Discovers Technetium

After receiving his degree, Segr? spent a year in the Italian army and then returned to the University of Rome as an instructor in physics. From 1930 to 1932, he studied at Hamburg under Otto Stern and at Amsterdam under Pieter Zeeman. He returned to Rome as associate professor of physics, where he again collaborated with Fermi. At Fermi's suggestion, Segr?'s early research into atomic spectroscopy, molecular beams, and x rays soon gave way to neutron physics, Fermi's own field of specialization. As part of Fermi's research team, Segr? was involved in the discovery which showed that slow neutrons are more effective in bringing about nuclear fission than are fast neutrons.

In 1936, Segr? was invited to become chairman of the department of physics at the University of Palermo. Shortly after accepting that position, he traveled to the United States to visit Ernest Orlando Lawrence and observe Lawrence's cyclotron at the University of California. During his visit, Segr? talked with Lawrence about a possible search for element number 43, one of the two elements known to exist that had not yet been discovered. The discovery of the element had been announced in the 1920s by German chemists Walter Noddack, Ida Tacke, and Otto Berg, but had not been confirmed. Only its missing space in the periodic table was evidence that it existed. Based on his earlier work with Fermi, Segr? reasoned that the bombardment of molybdenum (element 42) with neutrons should result in the production of an element with an atomic number one greater than that of molybdenum--the missing 43. When he left Berkeley to return to Italy, therefore, Segr? obtained from Lawrence a sample of molybdenum that had been bombarded with deuterons (in this case, the equivalent of neutrons). In the following year, in collaboration with a colleague, C. Perrier, Segr? was able to confirm chemically the presence of the anticipated element forty-three in the molybdenum sample. This was the first artificially produced new element in scientific history. Segr? and Perrier suggested the name technetium for the element from the Greek word teknetos, for "artificial."

Assists in the Discovery of Astatine and Plutonium 239

Segr? returned to the United States again in 1938 to work with Lawrence at Berkeley. While there, he designed an experiment by which he was convinced the last remaining missing element, number 85, could be prepared. Working with Dale R. Corson and K. R. MacKenzie, Segr? bombarded a small sample of polonium (element 84) with deuterons and obtained evidence for the existence of element 85. The team suggested the name astatine, from the Greek astatos, for "unstable," since the element is a radioactive element without stable isotopes. Segr?'s planned return to Italy in the summer of 1938 was interrupted by an unexpected development. The Fascist government of Italy had instituted a purge of Jews similar to that which was carried out by the Nazis in Germany. Segr?, a Jew, was consequently expelled from his post at Palermo. Segr?'s response to this snub, according to Isaac Asimov in Asimov's Biographical Encyclopedia of Science and Technology, was that he "shrugged and remained in the United States, becoming a citizen in 1944." Offered a research post at Berkeley, Segr? continued his work on neutron physics and artificial radioactivity. Two years later, he was involved in the discovery of yet another new element--plutonium--element number 94. This line of research, along with Segr?'s previous work on neutron physics, made him an invaluable asset during work on the development of the atomic bomb and, in 1943, he was appointed a group leader at the Los Alamos Scientific Laboratory of the Manhattan Project.

Discovers the Antiproton with Chamberlain

After the war, Segr? returned to Berkeley as professor of physics and began his collaboration with Owen Chamberlain on the search for the antiproton. In 1928, the English physicist Paul Dirac had predicted the existence of a particle identical to the electron in all respects except for its having a positive rather than a negative electrical charge. The discovery of the positron in 1932 by Carl David Anderson confirmed Dirac's prediction.

An extension of Dirac's original hypothesis suggested that all subatomic particles, not just the electron, should have their "anti-" counterparts. The search for the next antiparticle, a negatively-charged proton, was hampered by the fact that the particle was known to exist only at very high energies, such as the energy of cosmic radiation.

The construction of the 6.2 billion-electron-volt bevatron in the early 1950s provided another possible source of antiprotons. The accelerator had the potential to produce levels of energy at which the antiproton might be generated. Working with the bevatron, Segr? and Chamberlain finally discovered the hypothesized particle in 1955. For that discovery and the further confirmation it provided for Dirac's antimatter theory, Segr? and Chamberlain were awarded the 1959 Nobel Prize in physics. Segr? was married to Elfriede Spiro on February 2, 1936. After she died in 1970, he married Rosa Mines. Segr? had three children, Claudio, Amelia, and Fausta, by his first wife. In addition to his Nobel Prize, Segr? was awarded the Hofmann Medal of the German Chemical Society in 1954, the Cannizzaro Medal of the Accademia Nazionale de Lincei in 1956, and honorary doctorates from the University of Palermo, Gustavus Adolphus College, and Tel Aviv University. Segr? died in Lafayette, California, on April 22, 1989, of a heart attack.

Emilio Segr? was born in Tivoli, Rome, on February 1st, 1905, as the son of Giuseppe Segr?, industrialist, and Amelia Treves. He went to school in Tivoli and Rome, and entered the University of Rome as a student of engineering in 1922. In 1927 he changed over to physics and took his doctor's degree in 1928 under Professor Enrico Fermi, the first one tmder the latter's sponsorship.

He served in the Italian Army in 1928 and 1929, and entered the University of Rome as assistant to Professor Corbino in 1929. In 1930 he had a Rockefeller Foundation Fellowship and worked with Professor Otto Stern at Hamburg, Germany, and Professor Pieter Zeeman at Amsterdam, Holland. In 1932 he returned to Italy and was appointed Assistant Professor at the University of Rome, working continuously with Professor Fermi and others. In 1936 he was appointed Director of the Physics Laboratory at the University of Palermo, where he remained until I938.

In 1938 Professor Segr? came to Berkeley, California, first as a research associate in the Radiation Laboratory and later as a lecturer in the Physics Department. From 1943 to 1946 he was a group leader in the Los Alamos Laboratory of the Manhattan Project. In 1946 he returned to the University of California at Berkeley as a Professor of Physics, and still occupies that position.

The work of Professor Segr? has been mainly in atomic and nuclear physics. In the first field he worked in atomic spectroscopy, making contributions to the spectroscopy of forbidden lines and the study of the Zeeman effect. Except for a short interlude on molecular beams, all his work until 1934 was in atomic spectroscopy. In 1934 he started the work in nuclear physics by collaborating with Professor Fermi on neutron research. He participated in the discovery of slow neutrons and in the pioneer neutron work carried on in Rome 1934-1935. Later he was interested in radiochemistry and discovered together with Professor Perrier the element technetium, together with Corson and Mackenzie the element astatine, and together with Kennedy, Seaborg, and Wahl, plutonium-239 and its fission properties. His other investigations in nuclear physics cover many subjects, e.g., isomerism, spontaneous fission, and lately high-energy physics. Here he, his associates and students have made contributions to the study of the interaction between nucleons and on the related polarization phenomena. In 1955 together with Chamberlain, Wiegand, and Ypsilantis he discovered the antiproton. The study of antinucleons is now his major subject of research. Professor Segr? has taught in temporary appointments at Columbia University, New York, at the University of Illinois, at the University of Rio de Janeiro and in several other institutions. He is a member of the National Academy of Sciences (U.S.A), of the Academy of Sciences at Heidelberg (Germany), of the Accademia Nazionale dei Lincei of Italy, and of other learned societies. He has received the Hofmann Medal of the German Chemical Society and the Cannizzaro Medal of the Italian Accademia dei Lincei. He is an Honorary Professor of San Marcos University in Peru and has an honorary doctor's degree of the University of Palermo, Italy.

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