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Chinese American experimental physicist

Chien Shiung Wu (t=吳健雄; 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 Madame Curie" and the "Queen of Nuclear Research".

Chien Shiung Wu was born in the town of Liuhe, Taicang in Jiangsu province, China, on May 31, 1912, the second of three children of Wu Zhong Yi (t=吳仲裔 ) and Fan Fu Hua(t=樊復華). 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 and her father were extremely close, and he encouraged her interests passionately, creating an environment where she was surrounded by books, magazines, and newspapers. Wu's mother was a teacher and valued education for both sexes. Zhongyi Wu, her father, was an engineer and a social progressive. He participated in the 1913 Second Revolution while in Shanghai and moved to Liuhe after its failure. Zhongyi became a local leader. He created a militia that destroyed local bandits. He also established the Ming De School for girls with himself as principal.

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 fifty miles 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. Her elders advised her to "ignore the obstacles." This was similar to what her father always reiterated to her, "Just put your head down and keep walking forward." Although Wu ended up doing scientific research, her writing was considered outstanding thanks to her early training. Her Chinese calligraphy was praised by others. Before matriculating to National Central University Wu spent the summer preparing for her studies with her usual full force. She felt that her background and training in Suzhou Women's Normal School were insufficient to prepare her for majoring in science. Her father encouraged her to plunge ahead, and bought her three books for her self study that summer: trigonometry, algebra, and geometry. This experience was the beginning of her habit of self study, and it gave her sufficient confidence to major in mathematics in the fall of 1930. From 1930 to 1934, Wu studied at National Central University (now known as Nanjing University) and first 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. 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 (c=董若芬 ), on the in August 1936. Wu sorely 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. Because of her early achievements, the Oakland Tribune released an issue on her entitled "Outstanding Research in Nuclear Bombardments by a Petite Chinese Lady". The report quipped, A petite Chinese girl worked side by side with some top US scientists in the laboratory studying nuclear collisions. This girl is the new member of the Berkeley physics research team. Ms. Wu, or more appropriately Dr. Wu, looks as though she might be an actress or an artist or a daughter of wealth in search of Occidental culture. She could be quiet and shy in front of strangers, but very confident and alert in front of physicists and graduate students. China is always on her mind. She was so passionate and excited whenever "China" and "democracy" were referred to, as democracy meant so much in the 1940s. She is preparing to return and contribute to the rebuilding of China. Her plans would have to change when the Second World War began.

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. In September 1944, Wu was contacted by the Manhattan District Engineer, Colonel Kenneth Nichols. Wu was frustrated with her lack of professorships and volunteered to help out in the project. In the beginning, Wu was assigned to check the radiation effect of the reactor by building her own instruments; later, however, she was contacted for a much bigger role. The newly commissioned B Reactor, the first practical nuclear reactor ever built, which was located at the Hanford Site had run into an unexpected problem, starting up and shutting down at regular intervals. John Archibald Wheeler and partner Enrico Fermi suspected that a fission product, Xe 135, with a half life of 9.4 hours, was the culprit, and might be a neutron poison or absorber. Segrè then remembered the 1940 PhD thesis that Wu had done for him at Berkeley on the radioactive isotopes of Xe and told Fermi to "ask Ms. Wu". The paper on the subject was still unpublished, but after Fermi contacted Wu, Segrè visited her dorm room together with Nichols and collected the typewritten draft prepared for the Physical Review. The suspicions of Fermi and Wheeler came true, Wu's paper unknowingly verified that Xe 135 was indeed the culprit for the B Reactor; it turned out to have an unexpectedly large neutron absorption cross section. Wu, wary of her publication giving information to other nations on the arms race of the war, waited for a few months before November 1944, when she and Segrè submitted a complete study on these results, which was published months before the bombs were used the next year. Wu also used her findings in radioactive uranium separation to build the standard model for producing enriched uranium to fuel the atomic bombs at the Oak Ridge, Tennessee facility as well as build innovative Geiger counters. Like many involved physicists in their later years, Wu later distanced herself from the Manhattan Project due to its destructive outcome and recommended to the Taiwanese president Chiang Kai shek in 1962 to never build nuclear weapons. However, she was pleased to know that her family was safe in China. Years later, Wu in a rare occasion opened up on her involvement in building the bomb,Do you think that people are so stupid and self destructive? No. I have confidence in humankind. I believe we will one day live together peacefully.

After the end of the war in August 1945, Wu accepted an offer of a position as an associate research professor at Columbia. She would remain at Columbia for the rest of her career, and was first named associate professor in 1952, which made her the first woman to become a tenured physics professor in university history. In November 1949, Wu experimented with the conclusions of Einstein's EPR thought experiment, which called quantum entanglement "spooky action at a distance". Wu was the first to establish the phenomenon and validity of entanglement using photons through observing angular correlation, as her result confirmed Maurice Pryce and John Clive Ward's calculations on the correlation of the quantum polarizations of two photons propagating in opposite directions. Specifically, the experiment carried out by Wu was the first important confirmation of quantum results relevant to a pair of entangled photons as applicable to the Einstein Podolsky Rosen (EPR) paradox.

After the second world war, communication with China was restored, and Wu received a letter from her family, but plans to visit China were disrupted by the civil war. Due to the civil war and communist takeover led by Mao Zedong, Wu would not return to China until decades later to meet her surviving uncle and younger brother. Though Wu did not support Mao, she also did not particularly respect the now deposed president Chiang Kai shek and his wife Soong Mei ling. Wu found Soong to be class conscious, while Chiang, now based on Taiwan, was too complacent with foreign affairs and willing to let Soong handle diplomatic issues for him. However she decided to lend a bit more support to the Republic of China or Taiwan, as her teacher Hu carried close ties with the old republic. Due to the war, many were displaced and younger students would leave for the United States, while scholars in America could not return home. She missed China deeply and would often go with Luke to buy fabric to make her own qipao as a way to remember the country, which she always wore under her lab coat. Wu was also busy due to the birth of her son, Vincent (t=袁緯承 Yuán Wěichéng), in 1947. Vincent became a physicist like his parents and attended Columbia, following in Wu's footsteps. By the end of the civil war in 1949, Yuan joined the Brookhaven National Laboratory, and the family bought another home in Long Island. Yuan would regularly travel to Brookhaven in Long Island, and on weekends return to the family's Manhattan home near Columbia University where Wu worked as its first female physics professor. After the communists came to power in China that year, Wu's father wrote urging her not to return. Since her passport had been issued by the Kuomintang government, she found it difficult to travel abroad as places such as Switzerland did not recognize her passport. Sometimes her friend in Switzerland, physicist Wolfgang Pauli, had to secure her special visas just to enter the country. This eventually led to her decision to stay in the United States. With the help of Columbia chairman Charles H. Townes, Wu would become a US citizen in 1954.

In her post war research, Wu, now an established physicist, continued to investigate beta decay. Enrico Fermi had published his theory of beta decay in 1934, but an experiment by Luis Walter Alvarez had produced results at variance with the theory. Wu set out to repeat the experiment and verify the result. Wu was already heavily invested in working on beta decay as she took on the subject at UC Berkeley. In the year 1949, Wu completely established Fermi's theory and showed how beta decay worked, especially in creating electrons, neutrinos, and positrons. Supposedly, most of the electrons should come out of the nucleus at high speeds. After careful research, Wu suspected that the problem was that a thick and uneven film of copper(II) sulfate was being used as a copper 64 beta ray source, which was causing the emitted electrons to lose energy. To get around this, she adapted an older form of the spectrometer, a solenoidal spectrometer. She added detergent to the copper sulfate to produce a thin, even film. She then demonstrated that the discrepancies observed were the result of experimental error; her results were consistent with Fermi's theory. The speeds of the electrons that were commonly produced in experiments were now shown to be significantly slower. Thus by analyzing radioactive materials used by previous researchers, she proved that this was the cause of the problem and not from theoretical flaws. Wu thus established herself as the leading physicist on beta decay. Her work on beta decay became hugely beneficial to her later research and to modern physics in general.

Wu quickly became a full professor in 1958, and later on was named the first Michael I. Pupin Professor of Physics in 1973. Some of her impish students called her the Dragon Lady, after the character of that name in the comic strip Terry and the Pirates due to Wu's strictness and high standards of excellence. Regardless of this, Wu actually treated her students like her children and often ate lunch with them as well as got to know their entourages. She would do this while working from 8 am to 7 or 8 in the evening, with her pay still very low until it was drastically increased after Robert Serber was installed as the new chairman. Her discoveries proved to be important in physics and her work even crossed over to biology and medicine, where her contributions became extremely influential to certain studies on the molecular changes in red blood cells that caused sickle cell disease or anemia. In December 1962, Wu experimentally demonstrated a universal form and more accurate version of Fermi's old beta decay model, confirming the conserved vector current (CVC) hypothesis of Richard Feynman and Murray Gell Mann on the road to the Standard Model. She would release the results in the succeeding year. In this experiment, she was approached by Gell Mann after he and Feynman realized they needed an expert on experimental physics to prove their hypothesis. Gell Mann pleaded to Wu, "How long did Yang and Lee pursue you to follow upon their work?" Their hypothesis was influenced by Wu's demonstration that parity was not conserved, which brought other assumptions that physicists have made about the weak interaction into question. The question was if parity cannot be conserved in weak force interaction, then the conservation of charge conjugation could also be in dispute. Conservation and symmetry were basic laws that held true for electromagnetism, gravity, and the strong interaction, so it had been assumed for decades that they should also hold for the weak interaction until Wu debunked these laws. This was also crucial to the future discovery of the electroweak force. Wu worked with a number of student assistants including Y. K. Lee, Mo Wei or L. W. Mo, and Lee Rong Gen from Korea. Using a Van de Graaff accelerator at Columbia with proton, heavy hydrogen, and helium beams, they were able to perform their notable experiment. The beta ray spectra were measured in the magnetometer spectroscopy fifty feet from the accelerator. The beta decay sources B 12 and N 12 were produced in the magnetometer. The laboratories were locked during midnight and Mo had to create a duplicate key for everyone to sneak in and out of the laboratory during the wee hours of the morning. Mo would escort Wu to her Manhattan apartment home. Wu's discovery was presented at the Hilton hotel on January 26, 1963. Wu was pleased with the achievement and mentioned that it gave a complete foundation for Fermi's theory of beta decay as well as provide support for the theory of the two component neutrino, which her parity experiment first established. Feynman was very happy with the announcement and was so proud of the outcome that he called the CVC theory, together with his diagram and work in quantum electrodynamics, one of his finest scientific accomplishments. Later in the 1960s, Wu conducted more experiments on beta decay, specifically on double beta decay. She went inside a 2,000 ft deep salt mine below Lake Erie in Ohio to investigate on muonic atoms in which muons take the place of
electrons in normal atoms. The work conducted here would pave the way for its future discovery in the 1980s. Wu later wrote a textbook with Steven Moszkowski entitled Beta Decay, which was published in 1966. It was the first comprehensive study on beta decay, and the book quickly became the standard reference on the subject; it remains one of the standard references in the 21st century.

Wu's older brother died in 1958, her father the next year, and her mother in 1962. The United States State Department had imposed severe restrictions on travel to Communist countries by its citizens, so Wu was not permitted to visit mainland China to attend their funerals. She saw her uncle, Wu Zhou Zhi, and younger brother, Wu Chien Hao, on a trip to Hong Kong in 1965. After the 1972 Nixon visit to China, relations between the two countries improved, and she visited China again in 1973. Wu nearly visited in 1956, but decided to stay in the US to finish her famous experiment while her husband visited China. By the time she returned, her uncle and brother had perished in the Cultural Revolution, and the tombs of her parents had been destroyed. She was greeted by Zhou Enlai, who personally apologized for the destruction of the tombs. After this, she returned to China and Taiwan several times. During the late 20th century, Wu continued to be seen as the top experimental physicist in the world and many continued to ask for her guidance in proving certain hypotheses. Herwig Schopper, who was the director general of CERN, commented that physicists believed "if the experiment was done by Wu, it must be correct." She conducted experiments on Mössbauer spectroscopy and its application in the study of sickle cell anemia. She researched on the molecular changes in the deformation of hemoglobins that cause this form of anemia. She also did research on magnetism in the 1960s. Wu would later work on Bell's theorem, which showed results that confirmed the orthodox interpretation of quantum mechanics. In later life, Wu became more outspoken. She protested the imprisonment in Taiwan of the in laws of physicist Kerson Huang in 1959 and of the journalist Lei Chen in 1960. With the help of her teacher Hu Shih, Huang's in laws were eventually released on bail. Lei's sentence was reduced to ten years by President Chiang Kai shek. In 1964, she spoke out against gender discrimination at a symposium at the Massachusetts Institute of Technology. "I wonder," she asked her audience, "whether the tiny atoms and nuclei, or the mathematical symbols, or the DNA molecules have any preference for either masculine or feminine treatment", which garnered heavy applause from the audience. When men referred to her as Professor Yuan, she immediately corrected them and told them that she was Professor Wu. In 1975, physics department chairman Serber discovered that Wu had a much lower pay than her male colleagues but that she had never reported on it, so he adjusted her pay to make it equal to that of her male counterparts even if Wu only cared about the research at Columbia. Wu later quipped, In China there are many, many women in physics. There is a misconception in America that women scientists are all dowdy spinsters. This is the fault of men. In Chinese society, a woman is valued for what she is, and men encourage her to accomplishments, yet she remains eternally feminine. Wu's advocacies and conviction maintained a strong priority for the advancement of the sciences. Later in 1975 as the first female president of the American Physical Society, Wu met with President Gerald Ford to formally request him to create an advisory scientific body for the president, which President Ford granted and signed into law the formation of the Office of Science and Technology Policy. Wu also continued to be an advocate for human rights issues as she protested the crackdown in China that followed the Tiananmen Square massacre of 1989. In 1978, she was awarded the first Wolf Prize in Physics. One of its criteria considered those who were thought deserving to win a Nobel Prize without receiving one. She retired in 1981 and became a professor emerita.

Wu would spend most of her time in her later years visiting the People's Republic of China, Taiwan, and different American states. She became renowned for her steadfast promotion of teaching STEM subjects to all students regardless of gender or any other discriminating cause. Wu suffered a stroke on February 16, 1997, in New York City. An ambulance rushed her to St. Luke's–Roosevelt Hospital Center where she was pronounced dead. Her granddaughter, Jada Wu Hanjie, remarked "I was young when I saw my grandmother, but her modesty, rigorousness and beauty were rooted in my mind. My grandmother had emphasized much enthusiasm for national scientific development and education, which I really admire." During her retirement, Columbia hosted a celebration "to honor the First Lady of Physics", which garnered a huge reception, and subsequently held a banquet at the Qian Jia Fu restaurant along Broadway. The Polish American award winning professor Isidor Rabi called Wu one who had made greater contributions to science than Marie Curie, in spite of her nickname as the "Chinese Madame Curie". Maurice Goldhaber later quipped, "People avoid doing experiments in beta decay, simply because they know that Wu Chien Shiung will do a better job than anybody!" The other physicists were surveyed for their opinions on the finest female physicists, with Wu, Lise Meitner, and Curie coming in different orders depending on their standards; Leon Lederman noted that Curie and Wu were equally above Meitner while Valentine Telegdi ranked Wu first among female physicists. Regardless of the differing views, Wu was highly regarded by members of the scientific community. In accordance with Wu's wishes, her ashes were buried in the courtyard of the Ming De School that her father had founded and that she had attended as a girl.