Chien-Shiung Wu (; May 31, 1912 – February 16, 1997) was a Chinese-American particle and experimental physicist who made significant contributions in the fields of nuclear and particle physics. Wu worked on the Manhattan Project, where she helped develop the process for separating uranium into uranium-235 and uranium-238 isotopes by gaseous diffusion. She is best known for conducting the Wu experiment, which proved that parity is not conserved. This discovery resulted in her colleagues Tsung-Dao Lee and Chen-Ning Yang winning the 1957 Nobel Prize in Physics, while Wu herself was awarded the inaugural Wolf Prize in Physics in 1978. Her expertise in experimental physics evoked comparisons to Marie Curie. Her nicknames include the "First Lady of Physics", the "Chinese Marie Curie" and the "Queen of Nuclear Research".
Early life Chien-Shiung Wu was born in the town of Liuhe, Taicang, in Jiangsu province, China, on May 31, 1912. She was the second of three children of Wu Zhong-Yi () and Fan Fu-Hua (). The family custom was that children of this generation had Chien as the first character (generation name) of their forename, followed by the characters in the phrase Ying-Shiung-Hao-Jie, which means "heroes and outstanding figures". Accordingly, she had an older brother, Chien-Ying, and a younger brother, Chien-Hao.
Wu's father, Zhong-Yi, encouraged her interests in science, creating an environment where she was surrounded by books, magazines, and newspapers. Wu's mother was a teacher who valued education for both sexes. Zhong-Yi was an engineer and a social progressive. He participated in the 1913 Second Revolution while in Shanghai and moved to Liuhe after its failure. He then became a local leader who headed a militia that hunted local bandits. He also established the Ming De School for girls with himself as principal.
Education
Wu received primary education at the Ming De School. Wu grew up as a modest and inquisitive child in a well-to-do family. She did not play outside like the other children but instead would listen to the newly invented radio for pleasure and knowledge. She also enjoyed poetry and Chinese classics such as the Analects, and western literature on democracy that her father promoted at home. Wu would listen to her father recite paragraphs from scientific journals instead of children's stories until Wu learned how to read.
Wu left her hometown in 1923 at the age of 11 to go to the Suzhou Women's Normal School No. 2, which was from her home. This was a boarding school with classes for teacher training as well as for regular high school, and it introduced subjects in science that slowly became a growing passion for the young Wu. Admission to teacher training was more competitive, as it did not charge for tuition or board and guaranteed a job on graduation. Although her family could have afforded to pay, Wu chose the more competitive option and was ranked ninth among around 10,000 applicants.
In 1929, Wu graduated at the top of her class and was admitted to National Central University in Nanjing. According to government regulations of the time, teacher-training college students wanting to move on to universities needed to serve as schoolteachers for one year. In Wu's case, this was only nominally enforced. She went to teach at a public school in Shanghai, the president of which was the famous philosopher Hu Shih. Hu became a very notable political icon whom Wu saw as a second father and would visit Wu when she was in the United States. Hu was previously Wu's teacher when she took a few courses at National China College and was impressed when Wu, who sat in the front seat to be noticed by her hero, finished and perfected the first three-hour assessment in less than two hours.
From 1930 to 1934, Wu studied at National Central University, where she initially majored in mathematics but later transferred to physics. She became involved in student politics. Relations between China and Japan were tense at this time, and students were urging the government to take a stronger line with Japan. Wu was elected as one of the student leaders by her colleagues because they felt that since she was one of the top students at the university, her involvement would be forgiven, or at least overlooked, by the authorities. That being the case, she was careful not to neglect her studies. She led protests that included a sit-in at the Presidential Palace in Nanjing, where the students were met by Chiang Kai-shek.
For two years after graduation, she did graduate-level study in physics and worked as an assistant at Zhejiang University. She became a researcher at the Institute of Physics of the Academia Sinica. Her research on low-temperature gas spectroscopy was supervised by Ku Zing-whai, the only female physics professor at the institute and the first female physics PhD in the country. Ku had earned her doctoral degree at the University of Michigan and encouraged Wu to do the same. She became an important role model to the young Wu, who developed confidence and was sometimes blunt and honest when giving advice to close friends. Wu was accepted by the University of Michigan, and her uncle, Wu Zhou-Zhi, provided the necessary funds. She embarked for the United States with a female friend and chemist from Taicang, Dong Ruo-Fen (), on the in August 1936. Her parents and uncle saw her off at the Huangpu Bund as she boarded the ship. Though her family would survive the Second World War, she would only visit the remaining members of her family decades later when she made trips to China in the 1970s.
Early physics career Berkeley
Wu and Dong Ruo-Fen arrived in San Francisco, where Wu's plans for graduate study changed after visiting the University of California, Berkeley. She met physicist Luke Chia-Liu Yuan, a middle-class grandson from the concubine of Yuan Shikai (the self-proclaimed president of the new Republic of China and Emperor of China for six months before his death). As a result of his political lineage, Luke did not talk much about Yuan Shikai and Wu would tease him after she discovered the truth since her father once rebelled against Yuan Shikai. Yuan showed her the Radiation Laboratory, where the director was Ernest O. Lawrence, who would soon win the Nobel Prize for Physics in 1939 for his invention of the cyclotron particle accelerator.
Wu was shocked at the sexism in American society when she learned that at Michigan women were not even allowed to use the front entrance, and decided that she would prefer to study at the more liberal Berkeley in California. Wu was also influenced by her interest in the Berkeley facilities which included the first cyclotron of Lawrence, but her decision would disappoint Dong who studied at Michigan on her own. Yuan took her to see Raymond T. Birge, the head of the physics department, and he offered Wu a place in the graduate school despite the fact that the academic year had already commenced. Wu abandoned her plans to study at Michigan and enrolled at Berkeley. Her Berkeley classmates included Robert R. Wilson, who like others secretly admired Wu, and George Volkoff; her closest friends included post-doctoral student Margaret Lewis and Ursula Schaefer, a history student who chose to remain in the United States rather than return to Nazi Germany.
Wu missed Chinese cuisine and was not impressed with the food at Berkeley, so she always dined with friends such as Schaeffer at her favorite restaurant, the Tea Garden. Wu and her friends would get free meals that were not part of the menu due to her friendship with the owner. Wu applied for a scholarship at the end of her first year, but there was prejudice against Asian students from the department head Birge, and Wu and Yuan were instead offered a readership with a lower stipend. Yuan then applied for, and secured, a scholarship at Caltech. Birge, however, respected Wu for her talents and was the reason Wu could enroll even though the academic year already started.
Wu made rapid progress in her education and her research. Although Lawrence was officially her supervisor, she also worked closely with the famous Italian physicist Emilio Segrè. She quickly became his favorite student and the two conducted studies on beta decay, including xenon, which would provide important results in the future of nuclear bombs. According to Segrè, Wu was a popular student who was talented. In his autobiography, Nobel laureate Luis Alvarez said of Wu, I got to know this graduate student in this idle time. She used the same room next door, and was called "Gee Gee" [Wu's nickname at Berkeley]. She was the most talented and most beautiful experimental physicist I have ever met. Segrè recognized Wu's brilliance and compared her to Wu's heroine Marie Curie, whom Wu always quoted, but said that Wu was more "worldly, elegant, and witty." Meanwhile, Lawrence described Wu as "the most talented female experimental physicist he had ever known, and that she would make any laboratory shine." When it came time to present her thesis in 1940, it had two separate parts presented in very neat fashion. The first was on bremsstrahlung, the electromagnetic radiation produced by the deceleration of a charged particle when deflected by another charged particle, typically an electron by an atomic nucleus, with the latter being on radioactive Xe. She investigated the first study using beta-emitting phosphorus-32, a radioactive isotope easily produced in the cyclotron that Lawrence and his brother John H. Lawrence were evaluating for use in cancer treatment and as a radioactive tracer. This marked Wu's first work with beta decay, a subject on which she would become an authority.
The second part of the thesis was about the production of radioactive isotopes of Xe produced by the nuclear fission of uranium with the 37-inch and 60-inch cyclotrons at the Radiation Laboratory. Her second part on Xe and nuclear fission so impressed her committee, which featured Lawrence and J. Robert Oppenheimer, whom Wu affectionately called, "Oppie", that Oppenheimer believed that Wu knew everything about the absorption cross section of neutrons, a concept that would be applied when Wu joined the Manhattan Project.
Wu completed her PhD in June 1940, and was elected to Phi Beta Kappa, the US academic honor society. In spite of Lawrence and Segrè's recommendations, she could not secure a faculty position at a university, so she remained at the Radiation Laboratory as a post-doctoral fellow. Her plans changed when the Second World War began.
World War II and the Manhattan Project
Wu and Yuan were married at the home of Robert Millikan, Yuan's academic supervisor and the President of Caltech, on May 30, 1942. Neither the bride's nor the groom's families were able to attend due to the outbreak of the Pacific War. Wu and Yuan moved to the East Coast of the United States, where Wu became an assistant professor at Smith College, a private women's college in Northampton, Massachusetts, while Yuan worked on radar for RCA. She found the job frustrating, as her duties involved teaching only, and there was no opportunity for research. She appealed to Lawrence, who wrote letters of recommendation to a number of universities. Smith responded by making Wu an associate professor and increasing her salary. She accepted a job from Princeton University in New Jersey as the first female faculty member in the history of the physics department, where she taught officers of the navy.
In March 1944, Wu joined the Manhattan Project's Substitute Alloy Materials (SAM) Laboratories at Columbia University. She lived in a dormitory there, returning to Princeton on the weekends. The role of the SAM Laboratories, headed by Harold Urey, was to support the Manhattan Project's gaseous diffusion (K-25) program for uranium enrichment. Wu worked alongside James Rainwater in a group led by William W. Havens Jr., whose task was to develop radiation detector instrumentation.