Dr. Leona Woods Libby (1919–1986) was a physicist who played a vital role in the Manhattan Project and the early development of nuclear science in the United States. At just 23 years old, she was the only woman present when the world’s first nuclear reactor, Chicago Pile-1, went critical in 1942. Her work — particularly her design of the boron trifluoride neutron counter — was essential in confirming that a self-sustaining nuclear chain reaction had occurred.
Born in La Grange, Illinois, Libby showed remarkable academic promise from a young age. She attended Lyons Township High School and graduated in 1934 at just 14 years old. She then entered the University of Chicago, where she earned a B.S. in Chemistry by 19 and completed her Ph.D. in physical chemistry just three years later. She was quickly recruited to join Enrico Fermi’s team at the university’s Metallurgical Laboratory, where she became a key figure in reactor physics and instrumentation.
After the initial CP-1 experiment, Libby relocated with Fermi’s team to help oversee reactor development at Hanford. There, she contributed to resolving the unexpected xenon poisoning that threatened the B Reactor’s operation. Despite being pregnant during her work at Hanford, she concealed it under loose clothing to remain on the job — highlighting the barriers women scientists faced even at the height of wartime urgency.
Following the war, Libby held fellowships at the University of Chicago’s Institute for Nuclear Studies, Princeton’s Institute for Advanced Study, and Brookhaven National Laboratory. She later held academic positions at New York University, the University of Colorado, and UCLA, where she expanded her research into climate science, environmental studies, food irradiation, and engineering. Over her lifetime, she published more than 200 scientific papers and several books.
Libby remained a staunch defender of her work on the Manhattan Project, arguing that the bomb had shortened the war and prevented even greater loss of life. She was also a public advocate for nuclear energy and scientific responsibility.
Awards & Recognition
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Named one of Mademoiselle magazine’s “Women of the Year” in 1946 for her contributions to nuclear science
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Honored posthumously for her contributions to the Manhattan Project and early reactor development
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One of the few women prominently recognized in historical accounts of CP-1 and Hanford’s B Reactor
Sources
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National Museum of Nuclear Science & History (Atomic Heritage Foundation), “Leona Marshall Libby”
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National Park Service, “Leona Woods Marshall Libby”
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National Women’s History Museum, “Leona Libby”