Wu, Chien-Shiung

▪ 1998

      Chinese-born American experimental physicist (b. May 29, 1912, Liuhe, Jiangsu province, China—d. Feb. 16, 1997, New York, N.Y.), gained international acclaim for her research in nuclear and particle physics, especially on the process of radioactive beta decay. In 1956 she designed and conducted experiments that disproved what had been thought to be a universal symmetry law of nature: the principle of the conservation of parity. The principle held that the interactions of fundamental particles, such as the interactions that take place in decaying atomic nuclei, do not distinguish between mirror-image cases—that is, between right and left or clockwise and counterclockwise. Tsung-Dao Lee and Chen Ning Yang (Nobel laureates in 1957) believed that the principle of parity conservation does not hold for interactions between subatomic particles involving the weak force, one of the four basic forces of nature. They encouraged Wu to find experimental evidence that this was so. Working with a sample of the radioactive isotope cobalt-60 at an extremely low temperature, Wu found that in undergoing beta decay, a weak force interaction, the cobalt nuclei ejected electrons whose spins were predominantly left-handed; i.e., the spin rotation of the electrons was that of a left-handed screw. She thus confirmed the Lee-Yang hypothesis and caused a reformulation of the principle of parity conservation. In the early 1960s Wu and her associates conducted other experiments that confirmed a theory of vector-current conservation in nuclear beta decay that had been put forth by Murray Gell-Mann and Richard Feynman. After completing undergraduate studies in Nanjing, Wu traveled to the U.S., where she earned (1940) a Ph.D. in physics from the University of California, Berkeley. She taught at Smith College, Northampton, Mass., and Princeton University before joining the secret Manhattan Project, which produced the atomic bomb during World War II. Wu continued her research and taught at Columbia University, New York City, where she spent 37 years before retiring in 1980. Her book Beta Decay (1966) became a standard reference book. Wu's honours include the National Medal of Science and the Wolf Prize in physics. She also served as president of the American Physical Society.

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▪ Chinese-American physicist

born May 29, 1912, Liuhe, Jiangsu province, China

died Feb. 16, 1997, New York, N.Y., U.S.

      Chinese-born American physicist who provided the first experimental proof that the principle of parity conservation does not hold in weak subatomic interactions (weak force).

      Wu graduated from the National Central University in Nanking, China, in 1936 and then traveled to the United States to pursue graduate studies in physics at the University of California at Berkeley, studying under Ernest O. Lawrence. After receiving a Ph.D. in 1940, she taught at Smith College and at Princeton University. In 1944 she undertook work on radiation detection in the Division of War Research at Columbia University. Remaining on the university staff at Columbia after the war, she became Dupin professor of physics there in 1957.

      In 1956 Tsung-Dao Lee (Lee, Tsung-Dao) of Columbia and Chen Ning Yang (Yang, Chen Ning) of the Institute for Advanced Study, Princeton, New Jersey, proposed that parity is not conserved for weak nuclear interactions. With a group of scientists from the National Bureau of Standards, Washington, D.C., Wu that year tested the proposal by observing the beta particles given off by cobalt-60. Wu observed that there is a preferred direction of emission and that, therefore, parity is not conserved for this weak interaction. She announced her results in 1957. The success of this and similar additional experiments brought worldwide acclaim not only to Wu but also to Lee and Yang, who won the 1957 Nobel Prize for Physics for their work. In 1958 Richard P. Feynman (Feynman, Richard P.) and Murray Gell-Mann (Gell-Mann, Murray) proposed the conservation of vector current in nuclear beta decay. This theory was experimentally confirmed in 1963 by Wu in collaboration with two other Columbia University research physicists. She later investigated the structure of hemoglobin.

      Wu, who received the National Medal of Science in 1975 and served as president of the American Physical Society that year as well, was considered one of the premier experimental physicists in the world. She retired from her professorship at Columbia in 1981.

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