Leona Woods

Manhattan Project By 1942, when she was finishing writing up her thesis, she was the youngest and last of Mulliken's pre-war students, and was working alone because all her fellow students had become involved with war work. She met Herbert Anderson, who was working for Enrico Fermi. The two would go swimming together in Lake Michigan every afternoon at 5 pm. Anderson discovered that Woods was adept with vacuum technology from her research, and as soon as her PhD was finished, he hired her to work with the boron trifluoride detectors used to measure neutron flux.

Fermi's group constructed a nuclear reactor known as Chicago Pile-1 under the stands of Stagg Field, the university's abandoned football stadium, where Woods had once played squash. Walter Zinn did not want a woman involved in the dirty work of placing the graphite blocks, but Woods had plenty of work to do with the detectors and thermocouples, and used a small stack of graphite of her own to measure the effects of a radium-beryllium source on manganese foil to obtain a measure of the neutron cross section in order to calibrate the detectors. Her skills in glassblowing were useful in constructing the neutron detectors. She was the only woman present when the reactor went critical, asking Fermi "When do we become scared?"

In this 1946 photo of the Chicago pile team, Woods is the only woman, fourth from the left in the middle row. Laura Fermi remembered Woods as "a tall young girl built like an athlete, who could do a man's job and do it well. She was the only woman physicist in Enrico's group. At that time, her mother, who was also endowed with inexhaustible energy, was running a small farm near Chicago almost by herself. To relieve Mrs. Woods of some work, Leona divided her time between atoms and potatoes."

Like many scientists working on the project, Woods affected a casual attitude towards the danger posed by radiation. After a morning with Willard Libby soldering a canister containing a mixture of radium salt and beryllium metal, Woods absorbed about 200 roentgens, and her white blood cell count halved. The doctors gave her a lecture on how a woman has only a fixed number of egg cells, a proposition that Woods was skeptical of. She considered that the important thing was that the solder was done correctly. When the team moved to their new home at Argonne, Woods had a dormitory all to herself.

Woods married John Marshall in July 1943, and soon after fell pregnant. While she told Enrico Fermi, they agreed not to let Walter Zinn know, for fear that he would insist that she leave the reactor building. She covered up her pregnant belly with her baggy denim work clothes. She rode to work each day on an unheated Army bus, "arriving each morning barely in time to vomit before starting the day's work." The child, a boy called Peter, was born in 1944. She returned to work a few days later.

A team from Argonne was on hand for powering up the first reactor at the Hanford Site, where large reactors would produce plutonium for bombs. They watched the reactor in shifts, with John Marshall and others on the day shift, Enrico Fermi and Leona Marshall on the night shift, ending at midnight, and Don Hughes and John Wheeler on the swing shift. While the Marshalls were babysitting the reactor in Hanford, they left Peter with Leona's mother.

The reactor was powered up successfully, but after a few hours the power level dropped and the reactor shut down. Leona speculated that a water leak was the problem, rather than a radioactive poison. However, during the night the operators were able to power the reactor up again only to have it once more die away. The timings now pointed to a radioactive poison. After working through the numbers with slide rules and hand calculators, they determined the neutron cross section of the poison, which turned out to be xenon-135. Fortunately, the DuPont engineers had equipped the reactor with 50 percent more fuel tubes than the physicists had called for, and by loading them up, they managed to get the reactor started.

Asked many years later about how she felt about her involvement in the Manhattan Project, she said:

Post-war career After the war, Leona Marshall returned to the University of Chicago, where she became a fellow at Fermi's Institute for Nuclear Studies. Working with the Chicago Pile 3 heavy-water reactor, she found a way to 100 percent spin polarize neutron beams, and determined the refractive index of neutrons for various materials. Her second child, John Marshall III, was born in 1949. She became an assistant professor in 1953.

After Fermi died in 1954, the Marshalls separated. John Marshall returned to the Los Alamos Laboratory, while Leona, now effectively a single mother, became a fellow at the Institute for Advanced Study in Princeton, New Jersey in 1957. The following year she became a fellow at the Brookhaven National Laboratory, at a time when the focus of research in physics was shifting away from the nucleus and towards elementary particles. In 1960, she joined New York University as an associate professor of physics. She became a professor in 1962.

Three years later, she became a professor at the University of Colorado, researching high-energy physics, astrophysics and cosmology. She then became a staff member at RAND Corporation, where she would work until 1976. She began publishing as Leona Marshall Libby after she divorced Marshall in 1966 and married Willard Libby the next year. In 1973 she joined Libby at UCLA, where she became a visiting professor of environmental studies, engineering, engineering archaeology, mechanical aerospace and nuclear engineering.

She and Willard Libby helped organize UCLA's department of environmental science and engineering.

Like Willard Libby, she was a strong advocate of food irradiation as a means of killing off harmful bacteria, and advocated that legal and regulatory restrictions on its use be relaxed. She proposed that, instead of it being sprayed with malathion, fruit affected by the Mediterranean fruit fly could be treated with gamma rays. She was survived by her sons Peter and John, and four grandchildren. She also had two stepdaughters, Janet Eva and Susan Charlotte, from her second marriage.

Selected bibliography

Libby, L., M. (1969) Creation of an atmosphere for the moon. Rand Corporation. Libby, L., M. (1970) Fifty environmental problems of timely importance. Rand Corporation. Libby, L., M. (1979) The Uranium People. Crane, Russak. Libby, L., M. (1980) The upside down cosmology and the lack of solar neutrinos. Libby, L., M. (1982) Life Work of Nobel Laureate Willard Frank Libby. Libby, L., M. (1982) Carbon Dioxide and Climate. Pergamon. Libby, L., M. (1983) Past Climates: Tree Thermometers, Commodities, and People. Texas: University of Texas.

In popular culture Gabriella Greison is an Italian physicist, writer, and science communicator known for her work in reconstructing the lives of twentieth-century scientists, with particular attention to figures who have been overlooked in official historical accounts. In her book "La donna della bomba atomica", published by Mondadori, Greison focuses on the life of Leona Woods, the youngest scientist working on the Manhattan Project. As part of her research, Greison conducted on-site investigations in Los Alamos and Alamogordo, New Mexico, as well as in Chicago. She carried out archival research and consulted primary sources to collect materials related to Woods’ scientific work and personal life. By gathering documents dispersed across different archives and locations, she reconstructed significant portions of Woods’ story, including elements of her personal diary. Greison has also brought Woods’ story to the stage through a theatrical prose monologue, which she has performed in Italy and internationally, including in Washington, D.C.