Leona Woods Leona Woods ( August 9 , 1919 – November 10 , 1986 ) , later called Leona Woods Marshall and Leona Woods Marshall Libby , was an American physicist who helped build the first nuclear reactor and the first atomic bomb . At age 23 , she was the youngest and only female member of the team which built and experimented with the world ' s first nuclear reactor ( then called a " pile " ) , Chicago Pile - 1 , in a project led by her mentor Enrico Fermi . In particular , Woods was instrumental in the construction and then utilization of geiger counter s for analysis during experimentation . She was the only woman present when the reactor went critical . She worked with Fermi on the Manhattan Project , and , together with her first husband John Marshall , she subsequently helped solve the problem of xenon poisoning at the Hanford plutonium production site , and supervised the construction and operation of Hanford ' s plutonium production reactors . After the war , she became a fellow at Fermi ' s Institute for Nuclear Studies . She later worked at the Institute for Advanced Studies in Princeton , New Jersey , the Brookhaven National Laboratory , and New York University , where she became a professor in 1962 . Her research involved high - energy physics , astrophysics and cosmology . In 1966 she divorced Marshall and married Nobel laureate Willard Libby . She became a professor at the University of Colorado , and a staff member at RAND Corporation . In later life she became interested in ecological and environmental issues , and she devised a method of using the isotope ratios in tree rings to study climate change . She was a strong advocate of food irradiation as a means of killing harmful bacteria . Early life . Leona Harriet Woods was born on a farm in La Grange , Illinois on October 20 , 1919 , the second of five children of Wreightsill Woods , a lawyer , and his wife Mary Holderness Woods . She had two sisters and two brothers . She graduated from Lyons Township High School in La Grange at 14 , and received her BS in chemistry from the University of Chicago in 1938 , at the age of 19 . After passing her qualifying exams in chemistry , she approached the Nobel Prize for Physics laureate James Franck about being his graduate student , having been impressed by a talk he gave in 1939 on Brillouin zone s . Franck accepted , but told her that his professor had warned him that as a Jew , he would starve to death . Franck therefore warned Woods that " You are a woman and you will starve to death . " Despite the fact that Franck did not look malnourished , she took the warning seriously , and decided to instead become a graduate student of Robert Mulliken , who would one day become a Nobel laureate himself . Mulliken allowed her to choose her own research problem , and edited the final version before it appeared in the " Physical Review " . Her doctoral thesis , " On the Silicon Oxide Bands " , prepared under the supervision of Mulliken and Polish chemist Stanisław Mrozowski was accepted in 1943 . Mulliken , she later recalled , had twice told her " that perhaps not all he taught me was wasted . " His students , she noted , " agree that this is his highest praise . " 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 thermocouple s , 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 . Woods was the only woman present when the reactor went critical , asking Fermi " When do we become scared ? " 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 . Soon after , she 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 per cent more fuel tubes that 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 Studies 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 particle s . 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 worked until 1976 . In 1966 , she divorced John Marshall , and married Willard Libby , who had won the Nobel prize in 1960 . She later joined him at UCLA , where she became a visiting professor of environmental studies , engineering , engineering archaeology , mechanical aerospace and nuclear engineering in 1973 . Now known as Leona Marshall Libby , she became interested in ecological and environmental issues , and she devised a method of using the isotope ratios of Oxygen - 18 to Oxygen - 16 , Carbon - 13 to Carbon - 12 , and Deuterium to Hydrogen in tree rings to study changes in temperature and rainfall patterns hundreds of years before records were kept , opening the door to the study of climate change . 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 a prolific author , publishing over 200 scientific papers . While at RAND she wrote a book on " Creation of an Atmosphere for the Moon " ( 1969 ) . Her works include the autobiographical " The Uranium People " ( 1979 ) , a history of early atomic research . After Libby died in 1980 , she edited his papers with Rainer Berger , and published " The Life Work of Nobel Laureate Willard Libby " ( 1982 ) . Her last paper , on quasi - stellar objects , appeared in 1984 . She died at St . John ' s Medical Center in Santa Monica , California , on November 10 , 1986 , from an anesthesia - induced stroke . She was survived by her sons Peter and John , and four grandchildren . She also had two stepdaughters , Janet Eva Libby and Susan Charlotte Libby from her second marriage .