- Person
- Ben Mottelson
- Lived
- 1926–2022
- Field
- Nuclear physics
- From
- American-Danish
The story
Ben Mottelson was born in Chicago in 1926 to a Jewish family and grew up in La Grange, Illinois, in a home where scientific, political and moral questions were argued over freely. After a Harvard doctorate under Julian Schwinger he went to Copenhagen in 1950 on a travelling fellowship, began working with Aage Bohr, the son of Niels Bohr, and stayed in Denmark for the rest of his life.
At the time physicists had two incompatible pictures of the atomic nucleus. In the shell model, protons and neutrons move independently in orbits, which explained why certain numbers of them make especially stable nuclei. In the liquid drop model, the nucleus acts like a drop of fluid, which explained fission. James Rainwater had suggested that the outer particles might pull a nucleus out of its round shape. Bohr and Mottelson brought the pictures together. In papers in 1952 and 1953 they showed that the motion of individual particles can deform the whole nucleus, and that the deformed nucleus can rotate and vibrate collectively, producing rotational bands of energy levels like those of molecules. Experiments at the Copenhagen cyclotron soon found the predicted bands.
In 1958, after the BCS theory of superconductivity appeared, Bohr, Mottelson and David Pines showed that protons and neutrons pair up much like electrons in a superconductor, explaining why deformed nuclei rotate as if lighter than a rigid body. Their unified model, set out in the two-volume book Nuclear Structure (1969 and 1975), became the standard framework for describing the shapes and excitations of nuclei, knowledge that underpins nuclear science from energy to the study of how elements are made.
Mottelson later carried the same ideas into new territory, to clusters of metal atoms, quantum dots and clouds of ultracold atoms, which he called artificial nuclei, and his 1999 work on rotating Bose–Einstein condensates helped start a new field. He shared the 1975 Nobel Prize in Physics with Bohr and Rainwater, and he helped found the ECT* research centre in Trento, Italy.
Why it matters
The Bohr–Mottelson model is how physicists understand the shapes, spins and vibrations of atomic nuclei, a foundation of all nuclear science.
About Ben Mottelson
Chicago-born physicist who settled in Copenhagen and, with Aage Bohr, showed how atomic nuclei change shape, spin and vibrate, the standard picture of the nucleus that physicists still use.
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Sources
- Ben Roy Mottelson 1926–2022 CERN Courier
- Ben Roy Mottelson Physics Today
- Ben R. Mottelson, Biographical NobelPrize.org
- Ben Roy Mottelson Wikipedia
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