In the early 1950s, two of Wu's students, S. Ruby and B. Rustad, performed an experiment to investigate the beta decay in the transition from radioactive helium (He-6) to lithium (Li-6).
Wu held discussions with the students during the experimental process. The students published a short article in Physical Review Letters in 1952, followed by a long article in the Physical Review in 1955. They determined that the Fermi theory had a scalar (S) transition matrix, and the Gamow-Teller theory had a tensor (T) transition matrix.
As their experiment had Wu's endorsement, and she had a long record of precision, the Ruby-Rustad papers initially carried a lot of credibility. Later experiments, however, showed conflicting results.
Richard Feynman, M. Gell-Mannn (who won the Nobel Prize for a proposal of "quarks" and their interactions), R. Marshak and his student E. Sudarshan, and another physicist, J. Sakurai, all argued that the transition matrices in begta decay were vector (V) and axial vector (A). Before this was settled, some said that Marshak must be mad. How could the He-6 experiment be wrong?
Not long afterward, Maurice Goldhaber and two collaborators did an elegant experiment and proved that the V-A theory was correct. That settled the dispute.
Wu was very unhappy about the mistake made in the experiment of Ruby and Rustad. Ruby discussed the experiment in the Plaza Hotel (a landmark in New York City where Chiang Ching=Kuo, then Vice-Premier and later President of Taiwan, was shot while visiting the US) in January 1990, and regretted that he was so careless. He did not finish his Ph.D. degree, worked for IBM for some time, and resumed research work at Stanford University. Rustad died in the early 1960s.
The incident bothered Wu, She later built a larger experimental setup at Columbia, and did a similar experiment with He-6/ She and her collaborator Arthur Schwarzchild wrote a paper in 1958 pointing out the factors causing the mistake in the earlier experiment.
This bad mark did not change very much the position of authority in the field of beta decay that Wu enjoyed. Her reputation as the most precise experimentalist was intact. The saying in the physics circle was: “If the experiment was done by Wu, it must be correct.” [H. Schopper]
Wu believed in total devotion to research. She practiced this belief and expected the same of her students. She could not understand how a research could be distracted. She demanded perfection from her students. The most precise measurement, and accurate calculation in every step of every experiment. She asked her students to work all day on weekdays, Saturdays, and sometimes Sundays. She did not shy away from expressing her disappointment when her students failed to meet her demands.
In the 20th century, research in science had become much more competitive for funding support and recognition. As such, it was a far cry from the earlier cooperative atmosphere. People who knew her well believed that she was highly competitive by nature, and she felt that she had to double her effort in order to succeed, given what she had gone through in a rather oppressive environment.
Wu’s students recalled that she was the undisputed authority in the laboratory, and that she would never hesitate at all to correct any mistake that students had made. She preferred to lead a team of students, rather than collaborating with other scientists. She had very good insight, and always selected the most difficult—and the most fundamental—problems to attack.[Boehm] Students would argue with her about physics problems, but her opinions always turned out to be right. The students later found out that her opinions and understanding were results of years of experience. They very much admired her insight into physics [Koller].
As her experimental work faced increasing competition, Wu told her students not to show their data to visitors until it was published because it might be stolen. When guests pried, she switched to a particularly convoluted form of Chinese-English
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Wu was fundamentally a serious and reserved person, not that open and straightforward. In a way, she was a rather private person [Koller, Boehm].
One of her students remembered her rather defensive personality. There was a famous European scientist visiting Columbia. His English was not that Fluent, and he would occasionally ask students for the right word during his lecture. By contrast, Wu could never be comfortable without having prepared perfect lecture notes in advance [Ruby].
Sometimes, Wu would become really angry at the students. She would never yell at them, but would quietly go into her office, not talking to the students. Around that time, students considered installing a light beam detector at a certain height to monitor her mood [Koller]
Wu was nicknamed “Dragon Lady” in Columbia’s physics department in the early 1950s. “Dragon Lady” was the name given to a glamorous but dangerous Chinese beauty in a popular U.S. newspaper comic strip, Terry and the Pirates.
Wu’s signature qipao dress, her strong opinions, and her demands on the students naturally landed her with the nickname. Her students occasionally referred to her by this nickname behind her back, but did so with affection. Her students and contemporaries recalled that she was actually the most humane, generous and warm professor in the physics department. Most of the others were rather self-centered folks, with little concern for students. [Ruby, Koller]
Her manner was a reflection of her personality. She was basically a private person, and was rather reserved. Some felt that they did not know what her true intentions were. [collaborators Bohm and Ambler, students Koller and Ruby]
Wu also took care of and nurtured young students at Columbia University—quite different from the typical “self-centered” great physicists there. [Ruby.]
Wu’s concern that a child would add a certain distraction was not only for women. A male Ph.D. student in the 1950s got married and fathered a child. Wu was very surprised to see the student and the child together walking in the street. She found it unthinkable to have a child while still a graduate student [William Bennett]
