New York Times, February 18, 1997

Chien-Shiung Wu, 84, Top Experimental Physicist

By WILLIAM DICKE

NEW YORK -- Dr. Chien-Shiung Wu, a physicist who performed a historic experiment overturning what had been considered a fundamental law of nature, died on Sunday at St. Luke's-Roosevelt Hospital Center in Manhattan. She was 84 and lived in Manhattan.

The cause was a stroke, according to her husband, Dr. Luke C.L. Yuan, a retired experimental physicist.

Dr. Wu, the Michael I. Pupin Professor Emeritus of Physics at Columbia University, where she carried out research and taught for 37 years, was known throughout her career as a meticulously accurate experimental physicist who was in demand to put new theories to the test.

In her most famous experiment, announced in 1957, she and her colleagues overthrew a law of symmetry in physics called the principle of conservation of parity that had been considered immutable for 30 years. It held that in nuclear reactions, nature in effect does not differentiate between left and right. At one time, physicists were so certain of the validity of the law that they tried to make all of their observations fit it.

But Dr. Tsung-Dao Lee, also of Columbia, and Dr. Chen Ning Yang of the Institute for Advanced Study in Princeton, N.J., suggested that conservation of parity did not hold for interactions between subatomic particles involving the so-called weak force. (One of the four basic forces of nature, along with gravity, electromagnetism, and the strong force, the weak force plays a role in radioactive decay.)

Lee consulted with Dr. Wu, an expert in radioactive beta decay, in which an atom emits electrons. Lee and Yang suggested an experiment, but Dr. Wu had to find a way to carry it out, an extremely difficult challenge with the technology available at the time.

The experiment used cobalt 60 cooled to 0.01 degree above absolute zero (or minus 459.67 degrees Fahrenheit). Dr. Wu joined forces with a research team at the National Bureau of Standards in Washington, which had one of the few laboratories in the country that could chill materials to extremely low temperatures.

The cobalt 60, a radioactive isotope, was placed in a strong electromagnetic field, which made all the cobalt nuclei line up so they spun along the same axis.

Dr. Wu measured what happened when the cobalt nuclei broke down, giving off electrons. She used a device that counted the number of particles that shot out in the direction of the spin and those that did not.

If the law of conservation of parity was correct, the nuclei would give off equal numbers of particles in each direction. But Dr. Wu found that far more particles flew off in the direction opposite the spin of the nuclei, proving that nature differentiates between left and right.

The results were confirmed by other experiments.

Dr. Isador Rabi, a Nobel laureate in physics at Columbia, said at the time: "In a certain sense, a rather complete theoretical structure has been shattered at the base, and we are not sure how the pieces will be put together."

Lee and Yang were awarded the Nobel Prize in Physics in 1957 for their theoretical work in this area. Dr. Wu did not share the prize, but the playwright Clare Boothe Luce said at the time, "When Dr. Wu knocked out that principle of parity, she established the principle of parity between men and women."

Lee said on Monday: "C.S. Wu was one of the giants of physics."

Dr. Wu was born on May 29, 1912, near Shanghai. She received a bachelor's degree from National Central University in Nanjing in 1936 and a doctorate from the University of California at Berkeley in 1940.

She taught at Smith College and Princeton University before being asked to join the Manhattan Project, the Army's secret project to develop the atomic bomb in World War II. She helped develop a process to enrich uranium ore that produced large quantities of uranium 235, a fuel for the bomb.

As part of the project, an atomic pile was constructed at Hanford, Wash., in 1942, but its chain reaction stopped a few hours after it was started. The physicist Enrico Fermi suspected that a substance produced by nuclear fission was halting the reaction by capturing most of the neutrons.

He was reportedly told: "Ask Miss Wu." It turned out that a rare gas that she had studied in graduate school was responsible, and the problem was cleared up.

After the war, Dr. Wu joined Columbia as a research associate. She was named a full professor in 1958 and was appointed the first Pupin Professor of Physics in 1973.

In her research, she obtained the first successful measurements of low-energy electrons emitted by beta decay, providing experimental evidence for Fermi's theory of weak interactions in the nucleus. She was an author of "Beta Decay," published in 1965, a standard reference for nuclear physicists.

In 1975, Dr. Wu became the first woman to be elected president of the American Physical Society, the chief organization of physicists in the United States. She was also the first woman to receive the Cyrus B. Comstock Award of the National Academy of Sciences and the first woman to receive an honorary doctorate in science from Princeton. The university's president, Robert Goheen, said in presenting it in 1958 that Dr. Wu had "richly earned the right to be called the world's foremost female experimental physicist."

She also received the National Medal of Science, the nation's highest award for achievement in science, and the Wolf Prize in physics. Dr. Wu was elected to the National Academy of Sciences, and was elected to the Royal Society of Edinburgh as an honorary fellow.

Besides her husband, she is survived by a son, Vincent Yuan, of Albuquerque, N.M., who is a research scientist at Los Alamos National Laboratory.

Copyright 1997 The New York Times Company