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Radiation Detection & Separation Methods

The inventions and experiments of Chien-Shiung Wu, "the world's distinguished woman physicist of her time," helped to build the atomic bomb and to demolish a longstanding law of physics.

Chien-Shiung Wu was born in 1912 in Liu Ho, China, about 30 miles from Shanghai. Her education began at a grade school founded by her parents, and continued at the National Central University of Nanking, where she majored in Physics (BS 1934).

In 1936, Wu came to the US to pursue graduate studies at the University of California at Berkeley. There she had the privilege of working with Ernest O. Lawrence, inventor of the cyclotron. By the time she earned her PHD in 1940, Wu herself was known as one of the world's experts on nuclear fission.

Wu was already keenly aware, and openly critical, of male chauvinism in the sciences; to help counter the trend, she taught for some years at Smith College. In 1944, she was invited to join the Manhattan Project team at Columbia University in New York City. In support of the US' secret development of the atomic bomb, Wu developed better instruments to detect radiation, and invented a method of separating two types of electrons emitted from the nuclei of radioactive atoms. Wu's innovations allowed her team to monitor "beta decay" (nuclear radioactive emissions) and to separate out the fissionable isotope of uranium (U-235) from its more stable counterpart (U-238).

After the War, Wu remained at Columbia to teach: she worked her way through the ranks to become the first Pupin Professor of Physics in 1973, a position she held until her retirement in 1980.

The highlight of Wu's postwar career was an experiment she devised in 1956. In that year, two physicists, Tsung Dao Lee and Chen Ning Yang, had proposed that the "law of parity," which states basically that radiation is emitted symmetrically, did not hold for "weak" interactions. However, these physicists could not prove their theory. Using her expertise in beta decay, Wu did. At the National Bureau of Standards' cryogenics laboratory, she placed a salt of radioactive cobalt-60 in a strong magnetic field; supercooled the salt to minimize random thermal actions; and observed the pattern of electrons emitted by the isotope. As it turned out, the vast majority of electrons were vented in one direction, rather than equally on all sides, as the law of parity predicted.

Wu had proved that the law of parity did not apply universally. After Wu's experiment was duplicated and its conclusion confirmed, Lee and Yang won the Nobel Prize for Physics. Wu herself was overlooked --- a victim, it seems clear, of the very chauvinism she had fought throughout her career. Still, her colleagues knew the value of her work; and in the following years Wu did win a number of prestigious honors, including the National Medal of Science (1975). Wu was also the first woman to be granted an honorary doctorate from Princeton University (1958), to win the Research Corporation Award (1958), to win the National Academy of Sciences' Comstock Award (1964), and to be elected President of the American Physical Society (1973).

Even after her retirement, Chien-Shiung Wu continued to lecture in physics and to encourage young women to pursue careers in all the sciences. She died in 1997, but she remains a legend among physicists and an inspiration to all who aspire to invent, to experiment, and to challenge the scientific status quo.

[March 2000]