Chien-Shiung Wu

Chien-Shiung Wu was a Chinese-American experimental physicist whose cobalt-60 experiment showed that weak nuclear interactions violate parity symmetry.

Wu experiment: A 1956–1957 experiment measuring beta particles emitted by polarized cobalt-60 nuclei. Wu’s group used this setup to test whether beta decay treats left and right symmetrically.
Liu Hui: A Chinese mathematician of the third century known for commentaries on classical mathematical texts. Wu attended the school in Taicang named after Liu Hui before pursuing physics.
Ernest Lawrence: An American physicist who developed the cyclotron and won the 1939 Nobel Prize in Physics. Lawrence directed Berkeley’s radiation laboratory, where Wu completed her doctoral research.
Conservation law: A rule stating that a physical quantity remains constant during a specified process. Parity had been treated as conserved until Wu’s experiment challenged that assumption.
Cobalt-60: A radioactive isotope of cobalt that undergoes beta decay with a half-life of about 5.3 years. Its beta decay provided the radioactive nuclei at the center of Wu’s parity test.
Parity violation: The failure of a physical process to remain unchanged when spatial coordinates are inverted. Wu’s experiment found that weak-interaction beta decay distinguishes mirror-related directions.
National Central University: A Chinese university founded in Nanjing in 1902 and later re-established in Taiwan. Wu studied physics at this university before continuing her education in the United States.
Tsung-Dao Lee: A Chinese-American theoretical physicist who shared the 1957 Nobel Prize in Physics for work on parity nonconservation. Lee proposed testing parity in weak interactions and worked with Wu to connect theory and experiment.
CP violation: A failure of physical laws to remain unchanged under the combined operations of charge conjugation and parity inversion. Parity violation helped lead physicists to test whether the combined CP symmetry was conserved.
Sodium-22: A radioactive sodium isotope that decays by positron emission and electron capture. Follow-up work examined parity effects in positron emission from polarized sodium-22.

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