THE NUCLEUS Issue 2 Spring 2024

Maria Geoppert Mayer by Lillian Pao

The Nobel Prize Mayer won the Nobel Prize for Physics in 1963 for her idea that the atomic nucleus was made up of closed shells, where neutrons and protons tend to pair up together. Before her discovery, scientists generally considered the atomic nucleus as a homogenous blob (a drop of liquid), which was successful in explaining fission. Scientists also assumed that the nucleon interactions would be too strong to be accurately described by a shell model, which would display nucleons as independent structures. Perhaps because Mayer had less formal education in nuclear physics, she was less biased by existing theories. Mayer could see that in the atomic nucleus, neutrons and protons were distributed in shells and according to energy levels. These shells could explain the magic numbers (number of nucleons that are arranged in complete shells within the atomic nucleus, e.g. 2, 8, 20, 28, etc.). However, they don’t explain how repulsive forces this strong could hold together such ordered structures. At the suggestion of Enrico Fermi, Mayer explored the possibility of spin-orbit coupling in nuclei. She found that the nucleus was made up of closed shells in which neutrons and protons usually pair up. She famously compared the idea to a waltz, in which ‘some dancers spin in one direction and others in the opposite’.

What We Can Learn Maria Goeppert Mayer, who was described as ‘direct and unpretentious in manner’ by a report booklet from the University of California, was a passionate physicist who brought forward revelatory ideas to nuclear physics. To remember her, we should recognize her as a powerful role model for not only women in STEM, but also traditionally male dominated fields. Just like her, we can all transcend our limitations and pursue our interests.

When sending off her paper to the Physical Review for publication, she became aware that an experiment conducted by Hans Jensen and his colleagues had produced the same results. After the publication of both papers, Jensen met up with Mayer and co-authored the 1950 book Elementary Theory of Nuclear Shell Structure in which they further explored their scientific proof with sub-topics such as electrochemical and gasometric microanalysis. Jensen and Mayer then went on to share the 1963 Nobel Prize for their discovery of the nuclear shells.

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