Chien-Shiung Wu - Academic Career

Academic Career

The new Yuan family moved to the East Coast of the U.S., where Wu became a faculty member at, first, Smith College, then Princeton University in New Jersey for 1942－44, and finally at Columbia University in New York City, beginning in 1944 and continuing for many years after the war, all the way through 1980.

At Columbia University, Wu also did research and development for the Manhattan Project. She helped to develop the process for separating uranium metal into the U-235 and U-238 isotopes by gaseous diffusion. This was the process that was implemented on a gigantic scale at the K-25 Plant near Oak Ridge, Tennessee, whose construction began in 1944.

In her research at Columbia, Wu also worked to develop improved Geiger counters for measuring nuclear radiation levels.

At Columbia Wu knew the Chinese-born theoretical physicist Tsung-Dao Lee personally. In the mid-1950s, Lee and another Chinese theoretical physicist, Chen Ning Yang, grew to question a hypothetical law in elementary particle physics, the "Law of Conservation of Parity". Their library research into experimental results convinced them that this "Law" was valid for electromagnetic interactions and for the strong nuclear force. However, this "Law" had not been tested for the weak nuclear force, and Lee & Yang's theoretical studies showed that was probably not true. Lee and Yang worked out the pencil and paper design of several experiments for testing the "Conservation of Parity" in the laboratory. Lee then turned to Wu for her expertise in choosing and then working out the hardware manufacture, set-up, and laboratory procedures for carrying out the experiment.

Wu chose to do this for an experiment that involved taking a sample of radioactive cobalt 60 and cooling to cryogenic temperatures with liquid gasses. Cobalt 60 is an isotope that decays by beta particle emission, and Dr. Wu was also an expert on beta decay. The extremely low temperatures were needed to reduce the amount of thermal vibration of the cobalt atoms to practically nil. Also, Dr. Wu needed to apply a constant and uniform magnetic field across the sample of cobalt 60 in order to cause the spin axes of the atomic nuclei to all line up in the same direction.

For this cryogenic work, Dr. Wu needed the expertise and the facilities of the National Bureau of Standards in liquid gases to aid her. She thus traveled to NBS headquarters in Maryland with her equipment to carry out the experiments.

Lee and Yang's theoretical calculations predicted that the beta particles from the cobalt 60 atoms would be emitted asymmetrically if the hypothetical "Law of Conservation of Parity" proved invalid. Dr. Wu's experiments at the NBS showed that this is indeed the case: parity is not conserved under the weak nuclear interactions. This was also very soon confirmed by her colleagues at Columbia University in different experiments, and as soon as all of these results were published—in two different research papers in the same issue of the same physics journal—the results were also confirmed at many other laboratories and in many different experiments.

The discovery parity violation was a major contribution to high energy physics and the development of the Standard model. In recognition for their theoretical work, Lee and Yang were awarded the Nobel Prize for Physics in 1957. Wu received the first Wolf Prize in Physics in 1978 for her experimental work.

An additional important experiment carried out by Dr. Wu was the confirmation of the Pryce and Ward calculations on the correlation of the quantum polarizations of two photons propagating in opposite directions. This was the first experimental confirmation of quantum results relevant to a pair of entangled photons as applicable to the Einstein-Podolsky-Rosen (EPR) paradox, or situation.