Primer: Chien-Shiung Wu July 8, 2009Posted by Will Thomas in EWP Primer.
Tags: Chen-Ning Yang, Chien-Shiung Wu, Enrico Fermi, Ernest Lawrence, Maria Goeppert-Mayer, Noémie Benczer-Koller, Steven Moszkowski, Tsung-Dao Lee
Chien-Shiung Wu (1912-1997) was born in Shanghai, China and raised nearby in Jiangsu Province. Her father had been trained as an engineer and was the director of the Ming De School for Girls at the time of her birth. Wu finished her education at her father’s school in 1922 and went on to the Soochow School for Girls in Nanjing, where she studied physics and mathematics on her own while undertaking a more classical formal education. In 1930 she registered at the National Central University in Nanjing, and received a degree in physics in 1934. She was also active in the student protests there that followed the Japanese invasion of Manchuria in 1931.
Wu did x-ray crystallography research for two years at the Chinese National Academy of Sciences in Shanghai. In 1936 she sailed to America with financial support from an uncle in order to undertake graduate education at the University of Michigan. On her way, she stopped and visited the University of California at Berkeley, where she met Ernest Lawrence (and her future husband Luke Yuan). On learning that Michigan did not allow women in its student union, she opted to pursue her PhD at Berkeley instead, receiving it in 1940 for work on nuclear decay processes in xenon isotopes.
For the bulk of World War II, Wu was instructor in physics, first at Berkeley, then Smith College, then at Princeton (where she was the first ever female faculty member). She also consulted on problems of reactor physics for the Manhattan Project’s laboratory at Chicago and production facility at Hanford, Washington, in which her dissertation work proved valuable. In 1944, she moved to Columbia University, where she developed radiation detectors for the Manhattan Project. She would remain there for the rest of her career.
At Columbia, Wu continued her work on nuclear physics, focusing on beta decay processes, wherein electrons are radiated from the atomic nucleus and a nuclear neutron is converted into a proton, thereby transmuting the atom into the next higher element. She refined the experimental methodology for measuring the energy of emitted electrons, and was able to demonstrate that the energy spectrum conformed to results anticipated theoretically in the 1930s by Enrico Fermi, thereby validating his model of the beta decay process. This work brought her to prominence as an experimental physicist and a leading expert on beta decay, the subject of a 1966 textbook (appropriately titled Beta Decay) that she wrote with Steven Moszkowski.
In 1956, Wu’s expertise in beta decay experimentation served her well, when her Columbia colleague, theorist Tsung-Dao Lee, and Institute for Advanced Study theorist Chen-Ning Yang proposed that parity in particle interactions—a foundational principle of the burgeoning field of particle physics dictating the symmetry of interaction processes (if you don’t know, don’t ask)—might not be conserved in weak interactions (i.e. nuclear decay processes), in which parity conservation had never been measured. When Lee approached Wu with the proposal, she suggested a possible experimental arrangement that could test the theory.
Aware of the importance of Lee and Yang’s ideas about the nonconservation of parity—if they were true—Wu set to work immediately, bowing out of a conference and lecture tour trip to Europe and China with her husband. She arranged with Ernest Ambler (pictured with Wu above) of the National Bureau of Standards (NBS) to set up the experiment there. In December they found that the nonconservation of parity in the beta decays under observation was pronounced, a quality that soon became understood as a regular characteristic of weak interactions. With several NBS scientists, she published the results in a landmark January 1957 Physical Review article, just ahead of other measurements of parity nonconservation in weak interactions by groups at Columbia’s Nevis Laboratories and Chicago. The result had important implications for particle theory, and it made her career.
Following the famous NBS experiment, Wu continued to work in problems in nuclear physics for the remainder of her career. She had a legendary dedication to her work, keeping long hours in the laboratory and speaking enthusiastically and at length about physical problems. She demanded that her graduate students—training 33 over the course of her career—show similar discipline, and took a strong interest in their professional development.
Wu’s professional progress at Columbia was relatively slow in light of her achievements, although she had an easier career than other contemporary female physicists, such as Maria Goeppert-Mayer. She remained a research associate until 1952, when she was named an associate professor and became the first tenured woman in Columbia’s physics department. Following her outstanding work on the nonconservation of parity in beta decays, her career advanced more rapidly. She was named a full professor in 1958, the same year she was elected a member of the National Academy of Sciences (NAS).
In the 1970s, “Madame” Wu became a top-tier figure in the physics profession. She was named Michael I. Pupin Professor at Columbia in 1972, and was the president of the American Physical Society for 1975—the first woman to hold the position. She was awarded the National Medal for Science in 1975, and the first Wolf Foundation Prize for Physics in 1978. She took emeritus status in 1981. Following her retirement she was active in encouraging educational programs in physics in Taiwan and mainland China. After she died in 1997, her ashes were buried at a memorial designed by Tsung-Dao Lee at the Ming De School. Wu was one of only a very few women to enjoy prestigious careers in physics in the middle of the century, and was one of a significant group of Asian and Asian-American physicists to achieve prominence in the community at that time.
Wu’s main biographer is Rutgers physicist Noémie Benczer-Koller, who wrote the entry on Wu for Nina Byers and Gary Williams’ edited volume Out of the Shadows: Contributions of Twentieth-Century Women to Physics (2006), as well as the (I would say superior) NAS biographical memoir (pdf) in which the experimental arrangements are discussed in more detail. Additional information is taken from Tsung-Dao Lee and Richard Garwin’s Physics Today obituary, which is here (pdf). The AIP’s Emilio Segrè Visual Archives has a nice collection of photos.