A Sephardic family in Tivoli
Emilio Gino Segrè was born into a Sephardic Jewish family in Tivoli, near Rome, at the end of January 1905; because his birth was reported late, February 1 was registered as his official birthday. His father, Giuseppe Segrè, was an industrialist who owned a paper mill, and his mother was Amelia Susanna Treves. He had two older brothers, Angelo and Marco, and his uncle Gino Segrè was a professor of law.
He went to school in Tivoli and, after the family moved to Rome in 1917, in the capital. In 1922 he entered the University of Rome to study engineering, but he was more drawn to physics, and his life changed in 1927 when Franco Rasetti introduced him to a young professor named Enrico Fermi, who was looking for talented students.
One of the Via Panisperna boys
That September Segrè attended the Como Conference, where he heard lectures by Niels Bohr, Werner Heisenberg, Wolfgang Pauli, Max Planck and Ernest Rutherford. He switched to physics and in July 1928 became the first student to take his doctorate under Fermi’s sponsorship. After service in the Italian army in 1928 and 1929, he returned to the physics institute on Via Panisperna in Rome, where Fermi’s small group, later known as the Via Panisperna boys, was turning Italy into a centre of the new physics.
A Rockefeller Foundation fellowship took him in 1930 to work with Otto Stern in Hamburg and Pieter Zeeman in Amsterdam. Back in Rome as an assistant professor from 1932, he joined Fermi’s pioneering experiments with neutrons in 1934 and 1935, which included the discovery of slow neutrons, the basis of later nuclear reactors. In 1936 he married Elfriede Spiro, a Jewish refugee from Germany, at the Great Synagogue of Rome; he agreed with the rabbi to spend as little as possible on the wedding and give the balance to Jewish refugees from Germany.
The first artificial element
In 1936 Segrè became director of the physics laboratory at the University of Palermo in Sicily. That year he visited Ernest Lawrence’s Radiation Laboratory in Berkeley, California, home of the cyclotron, and was intrigued by the radioactive scrap metal from the machine. In February 1937 Lawrence mailed him a strip of molybdenum that had been part of the cyclotron and was emitting unusual radiation.
Working with the Palermo mineralogist Carlo Perrier, Segrè subjected the strip to careful chemical and theoretical analysis and proved that some of the radiation came from a previously unknown element, number 43. It was the first chemical element to be made artificially, a gap in the periodic table that nature had left almost empty. In 1947 they named it technetium, from the Greek word for artificial.
Exile and technetium-99m
In the summer of 1938 Segrè travelled to Berkeley to study short-lived forms of technetium that did not survive the trip by post to Italy. While he was on his way, Mussolini’s government passed racial laws barring Jews from university positions. Segrè could not go home. He brought his wife and young son to California, and Lawrence offered him a lowly research assistant’s post; when Lawrence realized that Segrè was trapped, he cut his salary to 116 dollars a month.
In these difficult circumstances Segrè did some of his most important work. In 1938, working with Glenn Seaborg at the Berkeley cyclotron, he isolated a metastable form of technetium, technetium-99m, and showed that it decays with a half-life of about six hours, the daughter of a longer-lived molybdenum isotope. Seaborg later recalled that the isotope decayed in a way that had never been observed before. Neither man could know that it would become the most widely used medical radioisotope in the world.
How patients benefit today
Technetium-99m is almost perfect for imaging the inside of the body. It gives off gamma rays that gamma cameras detect easily, with an energy similar to diagnostic X-rays, and its six-hour half-life is long enough for a scan but short enough that patients receive only a low dose of radiation. Because it is produced from molybdenum-99, which lasts several days, hospitals receive small generators from which they draw off fresh technetium as needed.
Other scientists turned Segrè and Seaborg’s discovery into medicine. At Brookhaven National Laboratory, Walter Tucker and Margaret Greene built the first technetium generator in 1958, and in 1960 Powell Richards first proposed using technetium as a medical tracer. Use spread rapidly in the 1960s. Today technetium-99m is used in tens of millions of diagnostic procedures every year, roughly 85 percent of nuclear medicine imaging, to examine the heart, bones, brain, thyroid, lungs, liver, kidneys and tumours. A patient having a bone scan for cancer or a heart scan for blocked arteries is very likely relying on the isotope Segrè helped find.
More elements, and the Manhattan Project
At Berkeley Segrè kept filling gaps in the periodic table. In 1940, with Dale Corson and Kenneth MacKenzie, he discovered element 85, astatine. With Chien-Shiung Wu he discovered xenon-135, which later proved important in the operation of nuclear reactors, and with Joseph Kennedy, Glenn Seaborg and Arthur Wahl he took part in producing plutonium-239 and studying its fission properties.
After the United States entered the war in December 1941, Segrè, still an Italian citizen, became an enemy alien. Physicists were leaving Berkeley for war work, and the department asked him to teach the remaining students, among them Owen Chamberlain and Clyde Wiegand, who would later become his collaborators. In 1943 he moved to Los Alamos, where he served as a group leader in the Manhattan Project, the wartime program that built the first atomic bombs, from 1943 to 1946. His group measured the radioactivity of fission products and found in 1944 that reactor-made plutonium contained plutonium-240, which fissioned spontaneously, a finding that forced a change in the project’s weapon designs. He became an American citizen in 1944.
A family destroyed
Segrè and his wife both feared for their parents in Europe, and their fears were justified. According to a family memoir, the Segrè sons who had reached America urged their parents to emigrate, but the couple felt too old for such a change and believed they would be safe. In June 1944 at Los Alamos he learned that his father was safe but that his mother had been seized by the Nazis in Rome. Amelia Treves Segrè was caught in the roundup of Rome’s Jews on October 16, 1943, and deported to Auschwitz, where she was killed. His father died in Rome in October 1944. Segrè never saw either of his parents again.
The racial laws that drove him into exile and the murder of his mother made him part of the great wave of Jewish scientists whom Fascism and Nazism pushed out of Europe and who went on to transform science in America. His marriage at Rome’s Great Synagogue, with its gift to refugees, shows a man who remained connected to the Jewish community even before the catastrophe.
The antiproton
After the war Segrè returned to Berkeley as a professor of physics. The years that followed were not easy: the university’s loyalty oath controversy poisoned the atmosphere, and, unhappy with relations among colleagues, he accepted a post at the University of Illinois before returning to Berkeley for good in 1952. By analogy with the positron, the antiparticle of the electron, physicists expected a negatively charged antiparticle of the proton, but none had been found. In 1955, using Lawrence’s new Bevatron accelerator, Segrè and Owen Chamberlain, together with Clyde Wiegand and Thomas Ypsilantis, detected the antiproton. Segrè and Chamberlain shared the 1959 Nobel Prize in Physics for the discovery, a decision that was controversial because Wiegand and Ypsilantis, co-authors of the discovery paper, did not share the prize.
Segrè was also a historian of his science. He edited Fermi’s papers, wrote a biography of Fermi in 1970 and two popular histories, From X-Rays to Quarks and From Falling Bodies to Radio Waves, and taught the history of physics after he retired. From 1958 to 1977 he edited the Annual Review of Nuclear Science, and he had been elected to the National Academy of Sciences in 1952. A keen photographer, he documented decades of physicists at work, and his photographs became the core of the American Institute of Physics’ Emilio Segrè Visual Archives.
Later years and legacy
Elfriede died in 1970, and in 1972 Segrè married Rosa Mines. He had three children with Elfriede: Claudio, born in 1937, Amelia, born in 1942, and Fausta, born in 1945. In 1955 the family had moved from Berkeley to nearby Lafayette. He retired from the University of California in 1972, returned briefly to teach at the University of Rome, and continued to write. He died of a heart attack while out walking near his home in Lafayette, California, on April 22, 1989, at the age of 84. His autobiography, A Mind Always in Motion, appeared in 1993.
His Nobel Prize was for the antiproton, but his most widespread gift to humanity may be a small isotope found in 1938 while he was a stranded refugee on a pittance salary. Every day, in hospitals across the world, technetium-99m lets doctors see the heart, bones and organs of patients without surgery, guiding diagnoses of cancer, heart disease and many other conditions.
Sources & further reading
Emilio Segrè, Biographical, NobelPrize.org · Emilio Segrè, Wikipedia · Technetium-99m, Wikipedia · Exploring the Golden Age of Italian Jews, Jewish Book Council · Researched from the sources above and checked against them. Spotted an error? Tell us.
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