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Dr. Chien-Shiung Wu: The First Lady of Physics

The Path to a Science Degree

When she arrived in California in 1936, Chien-Shiung Wu was fighting an uphill battle–one she’d been fighting her whole life. A young Chinese woman going to school would have been completely unheard of in her mother’s lifetime, and now she was abroad in pursuit of a PhD! Wu had traveled to the United States with hopes of starting graduate school at the University of Michigan, but she soon discovered that U-M did not even allow women past the front gates. This was a major road block, but Wu never let anything stop her from a career in science.

Despite the setback with U-M, and the fact that the academic year had already begun, Wu enrolled at the University of California, Berkeley. At Berkeley, Wu met her future husband, Luke Chia-Liu Yuan, and was introduced to Ernest O. Lawrence at the Radiation Laboratory, who would soon win the 1939 Nobel Prize in Physics for his invention of the cyclotron particle accelerator. She joined Lawrence’s lab and did research alongside Emilio Segrè, another soon-to-be Nobel Prize winner. Wu worked at the Radiation Laboratory while completing her PhD and returned as a post-doctoral fellow after discrimination against her race and gender made it difficult for her to secure a position elsewhere.

A Secret Project

In 1944, Wu joined the Manhattan Project, a top-secret research project to develop nuclear weapons during World War II before Nazi Germany could do so. She did meticulous work in experimental nuclear physics, and it wasn’t long before her reputation grew. The saying was, “if the experiment was done by Wu, it must be correct.” One of the experiments she would work on was called the B Reactor, which was built to create plutonium by bombarding uranium with neutrons. Inexplicably, the reactor shut down at regular intervals. Its designer, physicist and Nobel Laureate Enrico Fermi, was stumped until he received this piece of advice: “Ask Mrs. Wu.” Wu discovered that the reactor was also making something else besides plutonium. A different element, xenon, was being created in the reactor and absorbing all the neutrons, making plutonium production impossible. Thus, when the reactor was powered up, it worked until there was too much xenon and then shut down until the xenon decayed away.

Wu's Parity Breakthrough

After the war, Wu continued her physics research by studying beta decay, in which a radioactive element emits an electron and, inside the nucleus, a neutron turns into a proton. Physicists had thought that nuclear reactions obeyed certain laws like conservation of energy and another law called conservation of parity. Conservation of parity is the idea that an object behaves exactly the same as a mirror-image copy of itself.

Some theorists had predicted that in certain particle interactions, parity is not conserved, but Wu was able to prove it experimentally. She found that the electrons emitted in beta decay traveled in a preferred 8 PhysicsQuest 2019 direction relative to the orientation of the nucleus; in other words, the atom and its mirror image would behave differently.

This was a huge breakthrough in physics. However, Wu’s contributions went unacknowledged when her colleagues won the Nobel Prize in 1954. It wasn’t until 1978 that Wu was publicly acknowledged for her work: she was the first scientist awarded the Wolf Prize, which is considered to be the second most prestigious prize in science, after the Nobel.

Life After the Lab

Dr. Wu continued to make significant contributions to science throughout her career. She became the first female president of the American Physical Society (APS), and her 1965 book Beta Decay is still a reference for nuclear physicists. Wu retired in 1981 but continued to have a great impact on the science community. She was dubbed "the First Lady of Physics," and even has an asteroid named after her! In 1998, she was honored posthumously.