Chien-Shiung Wu

1912-1997

Chinese-American Physicist

Chien-Shiung Wu verified a theory for which her colleagues received a Nobel Prize in physics. An experimental physicist, Wu proved that the physical law of conservation of parity was invalid. Physicists had accepted this concept for thirty years before Wu's revelation, and the idea had been the foundation for theories regarding the universe's physical structure. Wu's remarkable investigation in nuclear physics demonstrated that science is dynamic and that physical laws can be fallible, reminding scientists to doubt assumed facts, to scrutinize their methodology and data to achieve accurate results, and to be receptive to new interpretations of the physical world.

Born on May 29, 1912, near Shanghai, China, Wu was born to Wu Zhongyi and Fuhua H. Fan Wu. Wu planned to become a scientist and her parents sent her to a boarding school, where she became fascinated by physics. She enrolled at the National Central University in Nanjing and prepared a thesis on x rays to earn a physics degree. While researching x-ray crystallography at Shanghai's National Academy of Sciences, Wu met a female physicist who had earned an American doctorate. Wu then decided to continue her education in the United States. In 1936 she began graduate studies at the University of California at Berkeley. Her professors included outstanding nuclear physicists, such as Robert Oppenheimer (1904-1967), who were devising new atomic theories.

Wu concentrated her research on atomic particles, writing her doctoral dissertation on two of her experiments. She had developed a method to separate two types of rays emitted during beta decay, a type of radioactivity in which the nucleus expels high-speed electrons and becomes another element. Wu observed that the electromagnetic energy discharged as a particle decelerated moving through matter, validating her hypothesis. She also investigated radioactive noble gases produced during uranium fission.

After Wu graduated in 1940, she remained at Berkeley to conduct research with Ernest O. Lawrence in the radiation laboratory. Wu became an authority on fission and was invited to present lectures nationwide. Wu married physicist Luke Cha-Liou Yuan and they moved to New Jersey, where she was the first female instructor at Princeton University. She then joined the Manhattan Project at Columbia University to design radiation detectors and to improve Geiger counters in addition to studying uranium enrichment and conducting neutron research. She stayed at Columbia after World War II. Wu returned to her research on beta decay and developed new techniques to study the shapes of particles' spectra and how they interacted during beta decay in an effort to achieve more precise experimental results.

In 1956 Wu agreed to test a theory for her colleagues Tsung Dao Lee and Chen Ning Yang. They wanted to prove that the principle of the conservation of parity, which stated that in nuclear structures an object and its mirror image behave symmetrically, was not always true. At the time, this principle was considered a fundamental law of physics. Wu examined beta rays, which are the electrons in the nuclei of radioactive substances, by chilling the nuclei to slow their thermal motion in order to observe the directions in which electrons were discharged during beta decay. She concluded that nuclear particles did not consistently behave symmetrically and, instead, often moved in the direction opposite to that of the spinning nucleus. Wu diligently verified her results and asked fellow researchers to duplicate her methodology.

On January 16, 1957, Wu announced her findings. Although Wu was co-author of articles regarding her experiments, Lee and Yang won the 1957 Nobel Prize in physics for conceptualizing the theory that she had verified. Wu, however, received other professional accolades, including the National Medal of Science, and was promoted to full professor. Research into beta decay continued to interest her and she published significant articles and books about her work, including nuclear physics applications to medicine.

ELIZABETH D. SCHAFER