Nobel Prize in Physics · 1995
Frederick Reines
He caught the 'undetectable' neutrino in 1956, opening a new window on stars and matter, after years spent testing nuclear weapons.
The Nobel citation: “for the detection of the neutrino”
- Born
- March 16, 1918, Paterson, NJ, USA
- Died
- August 26, 1998, Orange, CA, USA
- Shared with
- Martin L. Perl
- Affiliation at the time
- University of California, USA
Physics prize
1995
Shared with 1 other laureate.
Age that year
77years
Born in 1918.
Sources cited
22
Fact-checked September 24, 2026.
- Los Alamos says his neutrino detection is the only Nobel Prize-winning work ever done at the lab, though 18 Manhattan Project scientists were or became Nobel laureates.
- Before switching to a reactor, he and Clyde Cowan planned to catch neutrinos from an atomic bomb blast, with the detector falling down a shaft to ride out the shock wave.
- The Nobel Prize came in 1995, 39 years after the discovery. His partner Clyde Cowan had died in 1974, so Reines received it without him.
- As a student he sang so well that a Metropolitan Opera voice coach taught him for free, and he briefly thought about singing for a living.
- His first neutrino detector was big enough to hold a person, and his team used it to measure the natural radioactivity of living human bodies.
The breakthrough
First detection of the neutrino (the Reines-Cowan experiment, 1953-1956)
In one kind of radioactive decay, a neutron inside an atom's nucleus turns into a proton and shoots out an electron. The electrons came out with too little energy, as if energy were vanishing. In 1930 Wolfgang Pauli proposed a way out: an unseen, electrically neutral particle was carrying off the missing energy. It became known as the neutrino. The trouble was that neutrinos barely touch anything. In 1934 Hans Bethe and Rudolf Peierls concluded there was no practical way to catch one. Reines later put it this way: a typical neutrino could cross about 1,000 light-years of liquid hydrogen before hitting something. Reines and his Los Alamos colleague Clyde Cowan tried anyway. They first planned to use an atomic bomb as the source, then realized a nuclear reactor would work, because it pours out enormous numbers of neutrinos (strictly, antineutrinos) and runs for months. At the Savannah River reactor in South Carolina they put tanks of water, laced with cadmium, between large tanks of liquid that flashes when radiation hits it. Very rarely a neutrino strikes a proton in the water, making a positron and a neutron. The positron makes a flash at once; the neutron is caught by cadmium several millionths of a second later, making a second flash. That flash-then-flash pattern works like a secret knock: random noise rarely copies it. They counted about three such events an hour, and in June 1956 they told Pauli his particle was real.[1],[3],[4],[5],[6],[9]
“So why did we want to detect the free neutrino? Because everybody said, you couldn't do it.”
What it meant for humanity
The experiment settled a question that had hung over physics for a quarter of a century. By catching the particle far from where it was made, Reines and Cowan showed that the law of energy conservation holds inside the atomic nucleus, and they backed Enrico Fermi's theory of the weak force, which governs radioactive decay. It also opened a field. Reines spent four decades turning 'impossible' neutrino experiments into real ones. His teams were among the first to catch neutrinos made by cosmic rays in the atmosphere (1965), were the first to see antineutrinos from a reactor bounce off electrons (1976), and caught a key weak-force reaction on heavy hydrogen (1979), results that helped test the theory uniting electromagnetism and the weak force. His detectors grew from a 300-liter tank to the 8,000-ton IMB water detector in an Ohio salt mine. In 1987 IMB, together with Japan's Kamiokande, caught a burst of neutrinos from an exploding star, an event hailed as the birth of neutrino astronomy. IMB also gave the first reported hint that neutrinos change type, a finding later confirmed and honored with the 2015 Nobel Prize; one of the confirming experiments, Canada's Sudbury Neutrino Observatory, was conceived by Herbert Chen, who began as a postdoctoral theorist in Reines's group. His designs lasted: a 2020 review says the Reines-Cowan detector set design principles still used 60 years later, and it judges close-up monitoring of nuclear reactors with neutrino detectors now feasible. His first detector also gave a new way to measure radioactivity in living people. He built institutions too, as founding dean of physical sciences at the University of California, Irvine.
- In 1956 he and Clyde Cowan made the first detection of the neutrino, a particle predicted in 1930 that leading physicists had said could not practically be observed.[3],[4],[5]
- The IMB detector he co-led caught neutrinos from Supernova 1987A, hailed as the birth of neutrino astronomy. 'Supernova Early Warning System', a label he once put on detectors, now names a network linking neutrino experiments since 2005.[2],[5],[18]
- IMB data gave the first reported hint that neutrinos change type. Later experiments, including Canada's SNO, conceived by a former member of his group, confirmed it; that work won the 2015 Nobel Prize.[5],[16]
- A 2020 review says the Reines-Cowan detector set design principles still used 60 years later; over five million neutrinos have since been detected at reactors, and close-up reactor monitoring is now judged feasible.[17]
- His experiments on reactor antineutrinos scattering off electrons (1976) and neutrino reactions with heavy hydrogen (1979) gave timely tests of the electroweak theory of Glashow, Salam and Weinberg.[3],[5]
- His team used the first neutrino detector, big enough to hold a person, to measure the total radioactivity of living people, a new biophysical technique.[3],[5]
Impact in numbers
Reines gave the world knowledge rather than a product, so we record no benefit numbers. Proving that the neutrino exists confirmed that energy is conserved in radioactive decay and launched neutrino physics. That field has since shown that neutrinos change type and have mass, and it has let astronomers observe neutrinos from a collapsing star; scientists hope neutrinos will shed light on the early universe and dark matter. His detector designs, built around a delayed double flash, are still in use, and they may yet help monitor nuclear reactors for security purposes. Turning any of this into lives or dollars would be guesswork. We do record one harm. As a junior theorist on the Manhattan Project he shares, very slightly, in the deaths at Hiroshima and Nagasaki; we credit him with 0.1 percent, the share given to other minor contributors. His larger postwar role in nuclear testing is described in words, because fallout harms cannot be credibly assigned to one person.
Fundamental scienceSpaceTechnologyPeace
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.
- HarmMedium confidenceDirectSourced totalPeace
Deaths from the atomic bombings of Hiroshima and Nagasaki within two to four months
150–246
deaths caused, credited share
That is 0.1% 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 (the same range as the Bethe, Feynman, Bloch and Rotblat profiles; later cancer deaths excluded). Scope is direct because his own wartime work went into the project. Share 0.001: he arrived in 1944 as a new PhD and junior staff member in Feynman's T-4 group (Feynman's share: 0.005), whose main focus was diffusion theory for critical-mass calculations; he became a group leader about a year later (June 1946 per AHF). This matches Bloch and Rotblat (0.001) and is half of Rabi's 0.002. Thousands of others built the bombs, and US leaders chose to use them. His postwar test work (Operation Greenhouse) killed no one in war and is left unquantified. Result: 150,000 x 0.001 = 150 to 246,000 x 0.001 = 246 deaths credited.[5],[7],[15]
Sources: Radiation Effects Research Foundation (RERF); National Academy of Sciences; Atomic Heritage Foundation, National Museum of Nuclear Science & History
The double edge
Reines spent 15 years at Los Alamos, the US nuclear weapons laboratory, and much of it on nuclear weapons. He joined the Manhattan Project in 1944 as a junior theorist in Richard Feynman's group, which worked on calculations of critical mass. The bombs dropped on Hiroshima and Nagasaki killed an estimated 150,000 to 246,000 people within two to four months. After the war he became an expert on blast effects, analyzed results from several nuclear test series, and in 1951 directed the weapons and phenomenology program of Operation Greenhouse at Enewetak Atoll. Its tests included the first thermonuclear burn and the first test of fusion boosting, steps toward the hydrogen bomb. Enewetak's people were moved off their atoll for the testing program, often against their will, and its most contaminated soil and debris now sit under a concrete dome. Reines did worry about fallout, and his analyses helped build support for moving tests underground. Later, his neutrino experiment in a South African gold mine drew student protests.
- Major
Calculations for the first atomic bombs
In 1944 he joined the Manhattan Project's Theoretical Division at Los Alamos as a staff member in Richard Feynman's T-4 group, whose main focus was diffusion theory for calculating critical mass. The atomic bombings of Hiroshima and Nagasaki killed an estimated 150,000 to 246,000 people within two to four months. His wartime role was junior; by his own account he became a group leader about a year after arriving.[2],[5],[7],[15]
- Major
Nuclear tests on the road to the hydrogen bomb
After the war he analyzed and wrote up results of the Crossroads (1946), Sandstone (1948), Ranger and Buster-Jangle (1951) test series. In 1951 he directed the weapons and phenomenology program of Operation Greenhouse. Its George shot was the first thermonuclear burn and its Item shot the first test of fusion boosting, key steps toward the hydrogen bomb.[5],[7],[11]
- Moderate
Displacement and contamination at Enewetak
About 450 people lived on Enewetak before US testing, and they were evacuated, often involuntarily. The atoll hosted 43 nuclear tests from 1948 to 1958, including the two series Reines worked on there. Its most contaminated soil and debris were buried under the Runit Dome, which remains a major concern for the Marshallese. The decisions to test there were not his.[5],[12],[13],[14]
- Minor
Experiment in South Africa
From 1963 to 1971 his group ran a neutrino experiment in a South African gold mine with the University of the Witwatersrand. It drew protests from university students who objected to collaborating with South Africa, and charges at the United Nations that it involved secret nuclear weapons tests.[5]
Against the odds
Reines grew up in small-town America, and we found no record of antisemitism aimed at him personally. His family's story begins with migration. His parents came from the same small town in Russia, then the Russian Empire, where waves of anti-Jewish riots called pogroms had swept the southern and western provinces from 1881; their own reasons for leaving are not recorded. They were among more than two and a half million East European Jews who reached America between 1881 and 1924, when restrictive laws largely closed the door. The country he grew up in had barriers of its own. By 1922 Jewish students made up more than a fifth of Harvard's freshman class; the college then changed how it chose students, and by 1933 the Jewish share was back down to 15 percent; Yale and Princeton used similar methods. In the 1930s the radio priest Charles Coughlin, who at his peak regularly drew 30 million listeners, spread antisemitic lies. Reines himself was admitted to MIT and chose Stevens instead. His hardest obstacles were scientific. Leading physicists had said the neutrino could never practically be caught, his first attempt was swamped by background noise, and recognition came four decades late, after his partner had died.
—
Other
His parents emigrated from the same small town in Russia, then part of the Russian Empire, where pogroms struck Jews from 1881. They were among more than 2.5 million East European Jews who came to the US between 1881 and 1924, driven by persecution and poverty. Their own reasons for leaving are not recorded.[2],[5],[19],[20]
—
Discrimination
In his youth, elite colleges such as Harvard, Yale and Princeton cut the number of Jewish students they admitted, and in the 1930s the radio priest Charles Coughlin broadcast antisemitic lies to millions. We found no sign these barriers touched Reines, who was admitted to MIT and chose Stevens.[5],[21],[22]
1953
Other
Experts had long thought the neutrino practically undetectable, and Enrico Fermi could not suggest a detector design. The first attempt, at the Hanford reactor in 1953, was swamped by cosmic-ray background and gave only a weak hint of a signal.[3],[5]
1995
Other
The Nobel Prize came 39 years after the discovery. His partner, Clyde Cowan, had died in 1974 and could not share it; Reines said in his Nobel lecture that he regretted this.[3],[6]
Jewish background
Both parents, Israel and Gussie (Cohen) Reines, were Jewish immigrants from the same small town in Russia who met and married in New York. A paternal relative, his granduncle Rabbi Isaac Jacob Reines (1839-1915), founded Mizrachi, the Religious Zionist movement. His parents gave him religious observance and instruction, and he traced his first interest in science to a bored moment at religious school. His NAS memoir says he enjoyed Judaism's cultural side, but organized religion played little part in his adult life. His wife, Sylvia, was an early member and president of Hadassah in Los Alamos, and in 1988 he gave the Albert Einstein Memorial Lecture at the Israel Academy in Jerusalem.[2],[5],[10]
Key dates
March 16, 1918
Born in Paterson, New Jersey, the youngest of four children of Israel and Gussie (Cohen) Reines, Jewish immigrants from the same small town in Russia.[1],[2],[5]
1939
Earns an engineering degree at Stevens Institute of Technology, which he chose over MIT; a master's in mathematical physics follows in 1941.[2],[5],[8]
August 30, 1940
Marries Sylvia Samuels; they later have two children, Robert and Alisa.[2],[5]
1944
Completes a PhD at New York University on the liquid-drop model of nuclear fission and joins the Manhattan Project at Los Alamos in Richard Feynman's group.[2],[5],[7]
1946
By 1946 he is a group leader in the Los Alamos Theoretical Division (sources differ on the exact date), and he takes part in the Operation Crossroads nuclear tests at Bikini.[5],[7],[10]
1951
Directs the weapons and phenomenology program of Operation Greenhouse at Enewetak, a test series that included the first thermonuclear burn.[2],[5],[11]
1951
Takes a sabbatical to find a fundamental problem, settles on detecting the neutrino and teams up with Los Alamos colleague Clyde Cowan.[2],[3],[5]
June 14, 1956
After experiments at the Savannah River reactor in South Carolina, he and Cowan cable Wolfgang Pauli that they have detected the neutrino.[3],[4],[8],[10]
1959
Leaves Los Alamos to head the physics department at Case Institute of Technology in Cleveland.[2],[5]
February 23, 1965
His team deep in a South African gold mine records its first neutrino made by cosmic rays in the atmosphere, among the first such detections.[3],[5]
1966
Moves his Neutrino Group to the new University of California, Irvine, as founding dean of physical sciences.[2],[5]
February 23, 1987
The IMB detector he co-led, in an Ohio salt mine, catches a burst of neutrinos from Supernova 1987A.[2],[5]
1995
Wins half of the Nobel Prize in Physics for the detection of the neutrino; Martin Perl wins the other half for discovering the tau lepton.[1],[4]
August 26, 1998
Sources
- 1.Frederick Reines - Facts · NobelPrize.org (Nobel Prize Outreach)
- 2.Frederick Reines - Biographical · NobelPrize.org (from Les Prix Nobel, The Nobel Prizes 1995, Nobel Foundation, 1996), 1996
- 3.The Neutrino: From Poltergeist to Particle, Nobel Lecture by Frederick Reines, 8 December 1995 · NobelPrize.org (Nobel Foundation), 1995
- 4.The Nobel Prize in Physics 1995 - Press release (11 October 1995) · NobelPrize.org (Royal Swedish Academy of Sciences), 1995
- 5.Frederick Reines 1918-1998: A Biographical Memoir, by William Kropp, Jonas Schultz and Henry Sobel · National Academy of Sciences, 2009
- 6.Frederick Reines won a Nobel Prize for detecting the neutrino, by Ian Laird (National Security Science magazine) · Los Alamos National Laboratory, 2025
- 7.Frederick Reines · Atomic Heritage Foundation, National Museum of Nuclear Science & History
- 8.Nobel Pursuits: Frederick Reines' Path From Hoboken to the Manhattan Project and the Neutrino Discovery · Stevens Institute of Technology, 2025
- 9.Frederick Reines - Scientist of the Day · Linda Hall Library
- 10.Frederick Reines · Wikipedia
- 11.Operation Greenhouse · Wikipedia
- 12.Enewetak Atoll · Wikipedia
- 13.How the U.S. betrayed the Marshall Islands, kindling the next nuclear disaster, by Susanne Rust · Los Angeles Times, 2019
- 14.Marshall Islands Program · U.S. Department of Energy, Office of Environment, Health, Safety and Security
- 15.Frequently Asked Questions: How many people died as a result of the atomic bombings? · Radiation Effects Research Foundation (RERF)
- 16.The Nobel Prize in Physics 2015 - Press release · NobelPrize.org (Royal Swedish Academy of Sciences), 2015
- 17.Neutrino Detectors as Tools for Nuclear Security, by A. Bernstein, N. Bowden, B. L. Goldblum, P. Huber, I. Jovanovic, J. Mattingly (Reviews of Modern Physics 92, 011003) · arXiv (Cornell University), 2020
- 18.SNEWS 2.0: A Next-Generation SuperNova Early Warning System for Multi-messenger Astronomy (New Journal of Physics 23, 031201) · arXiv (Cornell University), 2021
- 19.A Century of Immigration, 1820-1924 (From Haven to Home: 350 Years of Jewish Life in America) · Library of Congress
- 20.Pogroms (Holocaust Encyclopedia) · United States Holocaust Memorial Museum
- 21.Getting In: The social logic of Ivy League admissions, by Malcolm Gladwell (review of Jerome Karabel, The Chosen) · The New Yorker, 2005
- 22.The Radio Priest: Charles E. Coughlin and American Antisemitism (Holocaust Encyclopedia) · United States Holocaust Memorial Museum
Fact-checked on September 24, 2026 by a separate AI fact-checking pass that re-opened the sources, with 4 corrections made. How we check
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