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Portrait of Emilio Segrè
Photo: Nobel foundation, https://nobelprize.org/nobel_prizes/physics/laureates/1959/segre-bio.html · Public domain via Wikimedia Commons

Nobel Prize in Physics · 1959

Emilio Segrè

A refugee from Fascist Italy's racial laws who helped find the proton's antimatter twin and an isotope used in millions of medical scans.

The Nobel citation: “for their discovery of the antiproton”
Born
February 1, 1905, Tivoli, Italy
Died
April 22, 1989, Lafayette, CA, USA
Shared with
Owen Chamberlain
Affiliation at the time
University of California, USA

Physics prize

1959

Shared with 1 other laureate.

Age that year

54years

Born in 1905.

Headline credited impact

17.4–39.9million people benefited

Diagnostic nuclear medicine scans using technetium-99m, the isotope Segrè and Seaborg discovered. How it was built

Sources cited

15

Fact-checked September 24, 2026.

  • He co-discovered technetium, the first element made artificially. A form of it that he found with Glenn Seaborg, technetium-99m, is used in about 80% of nuclear imaging scans.
  • Visiting Berkeley in 1938, he lost his Italian professorship to the racial laws. When his new boss learned he could not go home, he cut his pay from $300 to $116 a month.
  • His mother was seized in the Nazi roundup of Rome's Jews on 16 October 1943 and died at Auschwitz a week later. He learned of her capture from Robert Oppenheimer at Los Alamos.
  • His maternal grandfather, the architect Marco Treves, helped design the Florence synagogue, built around 1882.
  • He scattered a tiny sample of technetium, the element he co-discovered, on his father's grave in Rome. He noted that its radioactivity would last longer than any monument.

The breakthrough

Finding the antiproton, the proton's antimatter twin (1955)

Every kind of ordinary particle seems to have a mirror-image twin, an antiparticle, with the same mass but the opposite electric charge. When a particle meets its twin, both vanish in a burst of energy. Paul Dirac's theory predicted such twins, and in the early 1930s the electron's twin, the positron, was found. But physicists could not be sure that the proton, the heavy particle at the heart of every atom, had one. Making an antiproton takes a huge jolt of energy, so Berkeley's Bevatron accelerator was designed with enough power to create them, if they existed. In 1955 Segrè's group, with Owen Chamberlain, Clyde Wiegand and Thomas Ypsilantis, set a trap. Magnets picked out negatively charged particles that all had the same momentum. The team then measured each particle's speed by timing it over a set distance and with detectors that respond to how fast a particle moves. Picture balls of different weights, each hit equally hard: the heavier ones travel more slowly. Negative particles moving at exactly the speed expected for a proton's mass had to be antiprotons. At first only about one appeared every 15 minutes, among roughly 50,000 other particles. Stacks of photographic emulsion, a thick kind of film, were then exposed to the beam and caught antiprotons destroying themselves in bursts of energy, confirming the discovery.[2],[3],[5],[6]

“when the very foundations of civilization seemed in peril they generously welcomed their fellow scientists to the islands of safety then prevailing.”
Emilio Segrè, Nobel Banquet speech, Stockholm, 10 December 1959, praising the scientists who took in refugees like him. He added that he could never forget his own debt of gratitude.[4]

What it meant for humanity

The antiproton had no immediate practical use. Its value was understanding: it showed that the mirror symmetry between matter and antimatter, first seen with the light electron, also holds for the heavy particles inside atomic nuclei. Similar methods soon revealed the antineutron, and today CERN slows antiprotons down to build atoms of antimatter for study. Segrè's most tangible gift to ordinary people came from earlier work. In 1937 he and chemist Carlo Perrier identified element 43, technetium, the first element made artificially. Soon after reaching Berkeley in 1938, he and Glenn Seaborg found a form of it, technetium-99m (Tc-99m), that loses half its radioactivity in about six hours and gives off gamma rays similar to X-rays. In the late 1950s, Brookhaven National Laboratory chemists invented a generator that lets hospitals make the isotope on site, and in 1960 a physician first tried it for imaging. Doctors attach Tc-99m to drugs that carry it to the heart, bones, kidneys, lungs or brain, then follow its glow with a gamma camera. Its short life keeps the patient's radiation dose low. Cardiac stress tests, bone scans and searches for cancer all rely on it. Tc-99m now accounts for about 80% of nuclear imaging procedures, and the UN's scientific committee on radiation estimates about 40 million diagnostic nuclear medicine procedures a year worldwide. Segrè later became an honorary member of the Society of Nuclear Medicine. He also trained about 30 PhD students at Berkeley. The American Institute of Physics' photo archive of physics history, which gifts from his widow helped preserve and which holds many of his own pictures, bears his name.

  • Technetium-99m, which Segrè and Glenn Seaborg found in 1938, is used in about 80% of the world's nuclear imaging procedures, including cardiac stress tests and bone scans.[7],[11],[12]
  • The UN Scientific Committee on the Effects of Atomic Radiation estimates about 40 million diagnostic nuclear medicine procedures a year worldwide (2009-2018 data), up from 24 million a year in 1985-1990.[12]
  • In 1955 antiprotons made up about one in 50,000 particles in the beam and arrived about once every 15 minutes. By 1959 Berkeley's improved beams delivered about 10 a minute.[3]
  • The discovery settled doubts about whether protons, too, have antimatter twins. Similar methods soon found the antineutron, and CERN now slows antiprotons down to make atoms of antimatter.[3],[5],[6],[15]
  • He supervised about 30 PhD students at Berkeley and edited the Annual Review of Nuclear Science for 20 years.[6]

Impact in numbers

Segrè's Nobel discovery changed understanding rather than daily life: it confirmed that antimatter mirrors the heavy building blocks of atoms, not just electrons. His largest practical legacy came earlier, from technetium-99m, which underpins most nuclear imaging. We credit him with a modest 3% of that outcome, because turning the isotope into a clinical tool took Brookhaven's generator, gamma cameras, drug kits and a worldwide isotope supply chain. The high estimate counts each scan as one person helped, which overstates people because some patients are scanned more than once, so the low estimate halves it. We also count a share of the deaths from the atomic bombings, since his plutonium research and his Los Alamos group's measurements shaped the bomb dropped on Nagasaki. His textbooks, his histories of physics, his biography of Fermi and the photo archive that bears his name shaped how later generations learned the field.

HealthFundamental sciencePeace

Each number is the laureate’s credited share of a real-world outcome, cumulative to 2025. The whole outcome, the share of credit, and the reasoning are shown so you can check the arithmetic. Outcomes shared with other laureates are counted once on the impact page.

  • Low confidenceDirectModeledHealth

    Diagnostic nuclear medicine scans using technetium-99m, the isotope Segrè and Seaborg discovered

    17.4–39.9

    million people benefited, credited share

    That is 3% of 580 million–1.3 billion people benefited since 1961.

    How this number was built

    UNSCEAR: world diagnostic nuclear medicine ran 24M procedures/yr (1985-90), 32.5M (1991-96), 32.7M (1997-2007) and 40M (2009-18). Model: 0 in 1961 (first clinical trial 1960, per BNL) rising linearly to 24M at 1987.5, straight lines between survey midpoints, then 40M/yr through 2025: 318+170+277+418+480 = about 1.66 billion procedures. Tc-99m share about 80% (UNSCEAR, BNL). High = 0.8 x 1.66B = 1.33B, one person per scan. Low = 0.7 x 1.66B x 0.5 (assumes a lower early share and two scans per patient on average) = 580M. Share 0.03: Segrè co-discovered element 43 (with Perrier) and the Tc-99m isomer (with Seaborg), but use depended on Brookhaven's generator, gamma cameras, labeling kits and isotope supply, and others would likely have found the isomer soon. Credited: about 17M-40M.[6],[7],[11],[12]

    Sources: United Nations Scientific Committee on the Effects of Atomic Radiation; Brookhaven National Laboratory Newsroom; University of California Press (UC Press E-Books Collection); National Academy of Sciences / National Academies Press

  • HarmMedium confidenceDirectSourced totalPeace

    Deaths within two to four months of the 1945 atomic bombings of Hiroshima and Nagasaki

    1,500–2,460

    deaths caused, credited share

    That is 1% of 150,000–246,000 deaths caused since 1945.

    How this number was built

    RERF estimates acute deaths within two to four months at 90,000-166,000 in Hiroshima and 60,000-80,000 in Nagasaki, so 150,000-246,000 in total; later cancers are excluded, as in other profiles. Share 0.01: Segrè worked on the bomb directly. In 1941 he helped establish plutonium-239's fission properties with Kennedy, Seaborg and Wahl, and in 1944 his Los Alamos group's spontaneous-fission measurements showed a plutonium gun bomb would fail, forcing the implosion design of the Nagasaki bomb. His role bears mainly on Nagasaki; 0.01 of the total equals about 2.5-3% of Nagasaki's deaths. Thousands of scientists and workers built the bombs, others invented and engineered the implosion method, and US leaders chose to use them. Credited: about 1,500-2,500 deaths.[1],[6],[7],[13],[14]

    Sources: Radiation Effects Research Foundation; U.S. Department of Energy, Office of Scientific and Technical Information; National Academy of Sciences / National Academies Press; University of California Press (UC Press E-Books Collection); NobelPrize.org (from Nobel Lectures, Physics 1942-1962, Elsevier, 1964)

The double edge

Segrè's science also fed the atomic bomb. In 1941 he helped work out how plutonium-239 splits, the property that makes it a bomb fuel. At Los Alamos his group found that plutonium made in reactors fissions on its own too often for a simple gun-type bomb. That finding meant the lab had to rely on the implosion design, then unproven, which was used in the bomb that destroyed Nagasaki on 9 August 1945, killing an estimated 60,000 to 80,000 people within two to four months. Segrè later wrote that he was glad the project succeeded and relieved the war was over, that he saw little else President Truman could have done, and that fear of the bomb may have kept the superpowers from fighting a major war. The antiproton discovery also brought credit disputes. Two co-authors of the discovery paper, Clyde Wiegand and Thomas Ypsilantis, did not share the prize. Physicist Oreste Piccioni accused Segrè and Chamberlain of taking his ideas; by Segrè's account, the courts refused to hear Piccioni's 1972 lawsuit because the legal time limit had passed.

  • Major

    Plutonium and the Nagasaki bomb

    Segrè co-discovered the fission properties of plutonium-239 in 1941 and led a Los Alamos group from 1943. Its 1944 measurements showed a plutonium gun-type bomb would fail, which left the then-unproven implosion design as the way forward. That design was used in the Nagasaki bomb, which killed an estimated 60,000-80,000 people within two to four months.[1],[6],[7],[13],[14]

  • Minor

    Credit disputes over the antiproton

    The 1955 discovery paper had four authors, but only Segrè and Chamberlain shared the prize, and some felt Clyde Wiegand deserved a share. Oreste Piccioni claimed his ideas were taken; by Segrè's account, courts refused to hear his 1972 lawsuit because the statute of limitations had run out.[6],[7]

Against the odds

Italy's Jewish community, about 50,000 people in 1933, was well integrated, and until 1938 Jews could even join the Fascist Party. Like every Italian state employee, Segrè had been required by law to be a member. In 1938 Mussolini's regime began passing racial laws that pushed Jews out of government jobs, including teaching. Segrè, then a physics professor at Palermo, was on a summer research visit to Berkeley when the campaign began. His professorship was revoked, and he decided not to go home. He was 33, with a wife and a baby son, and no secure job. Ernest Lawrence gave him a research post, then cut his pay from $300 to $116 a month once he learned Segrè could not return to Italy. When the United States went to war with Italy in December 1941, Segrè became an 'enemy alien' under a curfew, and direct mail to his parents was cut off. After German forces occupied Rome in 1943, they hunted down its Jews. His father escaped and hid in a papal palace. His mother, Amelia, was arrested on 16 October 1943 and deported to Auschwitz, where she died on 23 October, the day her transport arrived. Segrè learned of her capture only in June 1944, at Los Alamos. His father died in Rome that October.

  • 1938

    Dismissal

    While he was on a research visit to Berkeley, Mussolini's government revoked his professorship at Palermo because he was Jewish.[7],[9],[10]

  • 1938

    Exile

    Fearing rising antisemitism and war in Europe, he chose to stay in the United States. His wife, a German-Jewish exile, and their son joined him in October 1938.[6],[7]

  • 1939

    Other

    When Ernest Lawrence learned that Segrè could not return to Italy, he cut his monthly pay at the Radiation Laboratory from $300 to $116. Segrè made ends meet with private funds he had kept abroad.[7]

  • 1941

    War

    When the United States went to war with Italy, he became an 'enemy alien' who had to register, obey a curfew and give up his radio, and direct mail to his parents was cut off.[7]

  • 1943

    Family killed

    His mother, Amelia Treves Segrè, was arrested in Rome on 16 October 1943 and deported on 18 October to Auschwitz. Italy's Holocaust records list her death on 23 October 1943, the day the train arrived.[7],[8],[9]

Jewish background

Both parents JewishIdentified as Jewish, secular

Segrè grew up in a prosperous Jewish family. His father's family had lived in the northern Italian town of Bozzolo for centuries. His mother, Amelia Treves, came from a Florentine Jewish family; her father co-designed the Florence synagogue. The Segrès kept no religious rites, and he had no bar mitzvah and little interest in theology. Yet he married in Rome's synagogue in 1936, and he found Jewish rites moving for the family history they carried. His wife, Elfriede Spiro, was a German-Jewish woman who had left Nazi Germany. He later became a governor of Tel Aviv University.[6],[7],[8],[10]

Key dates

  1. February 1, 1905

    Born in Tivoli, near Rome, into a prosperous Jewish family; his father ran a paper mill. He was actually born on 30 January, but the birth was registered late.[1],[6]

  2. 1928

    Earns his doctorate in physics at the University of Rome, the first doctoral student of Enrico Fermi.[1],[6]

  3. 1934

    With Fermi's group in Rome, helps discover that slowing neutrons down makes them far better at making elements radioactive.[1],[6]

  4. February 2, 1936

    Marries Elfriede Spiro, a German-Jewish woman who had left Nazi Germany, at Rome's synagogue. He asks that money saved on the ceremony go to German refugees.[7]

  5. 1937

    In Palermo, with chemist Carlo Perrier, identifies element 43, later named technetium, the first element made artificially, in a molybdenum foil from Berkeley's cyclotron.[1],[6]

  6. 1938

    On a research visit to Berkeley, learns that Fascist Italy's racial laws have cost him his professorship. He stays in the US; his wife and son follow in October.[6],[7],[10]

  7. 1938

    With Glenn Seaborg, finds technetium-99m, a form of technetium that later became the most widely used isotope in nuclear medicine.[7],[10],[11]

  8. 1940

    Co-discovers element 85, astatine, with Dale Corson and Kenneth MacKenzie.[1],[6]

  9. 1941

    With Joseph Kennedy, Glenn Seaborg and Arthur Wahl, helps isolate the newly discovered plutonium-239 and study how slow neutrons split it.[1],[6]

  10. October 16, 1943

    His mother, Amelia, is seized in the German roundup of Rome's Jews and deported to Auschwitz, where she dies on 23 October.[7],[8]

  11. 1944

    At Los Alamos, where he has led a group since 1943, his team shows that reactor plutonium fissions on its own too often for a gun-type bomb, forcing the switch to implosion.[1],[6],[7]

  12. 1955

    With Owen Chamberlain, Clyde Wiegand and Thomas Ypsilantis, discovers the antiproton at Berkeley's Bevatron.[2],[6]

  13. 1959

    Shares the Nobel Prize in Physics with Owen Chamberlain for the discovery of the antiproton.[2],[5]

  14. April 22, 1989

    Collapses and dies, aged 84, while on his regular walk near his home in Lafayette, California.[1],[6]

Sources

  1. 1.Emilio Segrè - Biographical · NobelPrize.org (from Nobel Lectures, Physics 1942-1962, Elsevier, 1964), 1964
  2. 2.Emilio Segrè - Facts · NobelPrize.org (Nobel Prize Outreach)
  3. 3.Properties of Antinucleons (Nobel Lecture, 11 December 1959) · NobelPrize.org, 1959
  4. 4.Emilio Segrè - Banquet speech (Stockholm, 10 December 1959) · NobelPrize.org, 1959
  5. 5.Award ceremony speech, Nobel Prize in Physics 1959 (Presentation Speech by Professor E. Hulthén) · NobelPrize.org, 1959
  6. 6.Emilio Gino Segrè, January 30, 1905-April 22, 1989, by J. David Jackson (Biographical Memoirs, Volume 81) · National Academy of Sciences / National Academies Press, 2002
  7. 7.A Mind Always in Motion: The Autobiography of Emilio Segrè · University of California Press (UC Press E-Books Collection), 1993
  8. 8.Treves, Amelia (record of a Shoah victim deported from Italy) · CDEC - Fondazione Centro di Documentazione Ebraica Contemporanea, Digital Library
  9. 9.Italy (Holocaust Encyclopedia) · United States Holocaust Memorial Museum
  10. 10.Segrè, Emilio Gino (Complete Dictionary of Scientific Biography entry by Robert Seidel, and other reference entries) · Encyclopedia.com
  11. 11.Celebrating the 60th Anniversary of Technetium-99m · Brookhaven National Laboratory Newsroom, 2018
  12. 12.UNSCEAR 2020/2021 Report, Volume I, Scientific Annex A: Evaluation of medical exposure to ionizing radiation · United Nations Scientific Committee on the Effects of Atomic Radiation, 2022
  13. 13.Frequently Asked Questions: How many people died as a result of the atomic bombings? · Radiation Effects Research Foundation
  14. 14.Manhattan Project: The Atomic Bombing of Nagasaki, August 9, 1945 · U.S. Department of Energy, Office of Scientific and Technical Information
  15. 15.The Antiproton Decelerator · CERN

Fact-checked on September 24, 2026 by a separate AI fact-checking pass that re-opened the sources, with 10 corrections made. How we check

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