Chien-Shiung Wu and Beta Decay
The third in a series of four biographies about overlooked women in science
Chien-Shiung Wu was born in a small town near Shanghai, China, in 1912. She received her education at a school started by her father, who uncommonly at the time believed in education for girls. Wu went on to study physics at a university in Shanghai where one of her professors had worked with Marie Curie. After graduation, she became a research assistant when her supervisor encouraged her to pursue advanced education in the United States. She made breakthrough discoveries in the laws of physics and contributed to the development of the atomic bomb.
In 1936, Wu went to San Francisco with financial help from an uncle. She enrolled at the University of California, Berkeley where she finished her Ph.D. in 1940.
As part of the Manhattan Project, Wu attended Columbia University in the 1940s and experimented with radiation and the enrichment of uranium. She was developing a process for separating uranium metal by gaseous diffusion. Gaseous diffusion produces a small separation between the molecules carrying uranium-235 and uranium-238. She is thought to have been the only person of Chinese origin to have worked on the project.
Wu stayed in the United States after the war. She began studying beta decay when offered a position at Columbia. Beta decay is a process where unstable atoms can become more stable. The two different types of beta decay are beta-minus and beta-plus.
Beta-minus decay
In an atom’s nucleus, a neutron decays into:
- 1 proton
- 1 electron
- 1 antineutrino
The electron and antineutrino leave the nucleus. This means the nucleus is left with one extra proton. When an atom increases its number of protons during beta-minus decay, the atom changes into a different element. For example: a carbon atom (6 protons) after going through beta-minus decay turns into a nitrogen atom (7 protons).
Beta-plus decay
In an atom’s nucleus a proton decays into:
- 1 neutron
- 1 positron
- 1 neutrino
The positron and neutrino leave the nucleus. This means the nucleus is left with one less proton. When an atom loses a proton during beta-plus decay, it likewise changes into a different element. For example: after going through beta-plus decay a carbon atom (6 protons) turns into a boron atom (5 protons).
Wu made significant advancements, including the first confirmation of Enrico Fermi’s theory of beta decay.
By 1956, her expertise in beta decay was widely known and she was contacted by the theoretical physicists Tsung Dao Lee and Chen Ning Yang. They wanted her to devise an experiment to prove one of their theories: that the law of conservation of parity did not hold true during beta decay. Parity is defined as “the state or condition of being equal.”
Simply put, “The law of parity states that all objects and their mirror images behave the same way, but with the left hand and right hand reversed.” (Atomic Heritage)
This law was accepted for 30 years until Wu’s experiments using the radioactive form of cobalt, cobalt-60, disproved it. She demonstrated that identical nuclear particles do not always act the same.
Lee and Yang received the 1957 Nobel Prize in Physics for their theory. Wu’s work was not mentioned.
Nevertheless, Wu made many more contributions to the scientific world throughout her career.
Nina Byers, a retired physics professor at the University of California, Los Angeles, declared Wu one of the best experimental physicists of her time. “People found [the Nobel decision] outrageous,” said Byers.
Wu passed away from a stroke in 1997 in New York at age 84.
Her accomplishments include, but are not limited to:
- The National Medal of Science
- The Comstock Prize
- The first honorary doctorate awarded to a woman at Princeton University
- The 1978 Wolf Prize in Physics
- Her widely-referenced book Beta Decay, published in 1965
“Beta decay was…like a dear old friend. There would always be a special place in my heart reserved especially for it.”
–Chien-Shiung Wu
