Ben R. Mottelson | Biography

Ben R. Mottelson was born in Chicago in 1926 to Goodman Mottelson and Georgia Blum. In 1943 he enlisted in the United States Navy, was sent to Purdue University for officer training and then, at the war's conclusion, returned to Purdue to complete his B.S. degree. Upon graduation from Purdue in 1947, Mottelson began his doctoral program in physics at Harvard University. He was granted his Ph.D. in 1950 for a dissertation on nuclear physics written under the direction of Nobel Laureate Julian Schwinger.

From 1950 to 1957 Mottelson conducted postdoctoral research in Copenhagen, Denmark. At the conclusion of this period, Mottelson was appointed to the staff at the newly-created Nordic Institute for Theoretical Atomic Physics (NORDITA). Mottelson has continued his association with NORDITA ever since and, in 1981, was named director of the institute.

During his early years in Copenhagen, Mottelson's primary research interest was the structure of the atomic nucleus. In that research he collaborated with Aage Bohr, one of six sons of the Danish physicist Niels Bohr. The problem with which Mottelson and Bohr dealt was that two quite different theories of nuclear structure had been proposed in the preceding fifteen years. One, the liquid-drop model, had been suggested by Niels Bohr in 1936. According to that model, the nucleus acts as if it were made from an incompressible fluid that oscillates back and forth around a basically spherical shape. The liquid-drop model successfully described a number of known nuclear properties, especially the phenomenon of nuclear fission.

Over time, however a number of deficiencies in the Bohr model became apparent. Finally, in 1949, Maria Goeppert-Mayer and a team led by J. H. D. Jensen independently suggested an alternative theory, the shell model. According to this theory, nucleons (protons and neutrons) travel in specific orbitals within the nucleus, roughly similar to the way electrons orbit the nucleus in specific energy levels. The shell model explained a number of phenomena for which the liquid-drop model had been inadequate, but it failed when applied to many properties observed for the nucleus as a whole.

Mottelson and Aage Bohr were able to find a way of combining the liquid-drop and shell models into a single collective theory of nuclear structure. Their work was aided by the work of James Rainwater, with whom Aage Bohr had worked while at Columbia University from 1949 to 1950. Rainwater had suggested in a 1950 paper that the outermost nucleons in a nucleus might undergo dislocations that would change the shape of the nucleus from spherical to oblate. That idea provided one of the first links between the liquid-drop and shell models of the nucleus.

Between 1950 and 1953, Mottelson and Bohr expanded upon and revised Rainwater's theory. They suggested a mechanism by which nucleons can still be assigned energy levels within the nucleus, but in such a way that their motions can produce overall liquid-drop-type effects. For their contributions to the development of this model, Mottelson, Bohr, and Rainwater shared the 1975 Nobel Prize in physics.

Mottelson married Nancy Jane Reno in 1948; they have two sons and a daughter. Mottelson and his wife became Danish citizens in 1971.