Chien-Shiung Wu is known primarily for one particular experiment, the first experiment to show unequivocally and definitively that the previous assumption that parity was preserved in the weak nuclear force was invalid. However, at that time she had already made many other substantial contributions to nuclear physics and she was recognized as one of the greatest experimental physicists of her time. She had an unparalleled ability to assess the demands of the experiment, as well as the capabilities and limitations of the tools at her disposal. She easily identified possible sources of error, both in her own work and that of others, and used that knowledge in planning the next experimental investigation. When she tested theoretical models by searching for phenomena not yet observed, she was always alert to pitfalls or difficulties that could invalidate the investigation, and she did what was necessary to avoid them. A great scientist whose story began on May 31, 1912.
She did her doctorate on crystal structure by X-ray diffraction under the direction of Professor Shi Shiyuan, who had returned from the Curie Institute in 1933. After graduating from Nanjing University with top honors, she worked for a year as an assistant professor at the Department of Physics at Hangzhou University and later took over as a research assistant in the physics laboratory of the Shanghai Academy. She there she continued her crystallography work under the supervision of Professor Jing-Wei Gu. She the latter had just returned from the United States and, since there was no graduate program in China, she encouraged Chien-Shiung to travel there to pursue her career.
At her insistence, she sent an application for admission to the University of Michigan whose response could not be better. Not only did they admit her to her Physics Department, they also supported her to pursue research in atomic spectroscopy. Her uncle offered to provide the necessary financial means for her to follow her dream so that, at the end of the summer, she sailed from Shanghai on her way to Ann Arbor … a destination that she never set foot on.
hien-Shiung Wu began working in Berkeley, under the direction and supervision of Emilio Segre. During the development of her doctoral thesis, he used the cyclotron to study the nuclear fission products of uranium-235, the hot topic at the time. Nuclear fission is a reaction in which a heavy nucleus, bombarded with neutrons, becomes unstable and decomposes into two nuclei of similar size, releasing a certain number of neutrons (usually two or three). The resulting nuclei are radioactive and disintegrate into “daughter” nuclei which, if unstable, undergo a new disintegration. The process continues until, finally, a stable nucleus is produced.
In the specific case of uranium-235, neutron bombardment converts it into uranium-236, which is extremely unstable and is divided into Krypton and Barium with the release of three neutrons; or in xenon and strontium, with the release of two. The properties that Wu analyzed in the members of the resulting product chain allowed him to study the interaction of nuclear forces in more detail.