(b. 26 January 1911 in Blankenburg, Germany; d. 20 March 1993 in Dallas, Texas), experimental physicist, educator, and academic administrator who won the Nobel Prize in physics in 1955 for his precision measurement of the magnetic moment of the electron that, along with related discoveries, furnished a fundamental piece of evidence leading to decisive advances in the theory of quantum electrodynamics.
Kusch was born to John Matthias Kusch and Henrietta van der Haas. His father was a Lutheran missionary who named his son after Saint Polykarp, a second-century bishop and martyr whose feast day is 26 January, the day of Kusch’s birth.
In 1912 the Kusch family came to the United States, moving to various locations in the Midwest before settling in Cleveland, where his father, after an unsettled period, secured a position with a book publisher. Kusch attended public schools in Cleveland and became a naturalized American citizen in 1922 at the age of eleven. After his high school graduation in 1927, he matriculated at Cleveland’s Case School of Applied Science (later named Case Western Reserve University), intending initially to study chemistry and chemical engineering. His interests soon changed to physics and he graduated with a bachelor of science degree with a major in physics in 1931. Later in life he observed: “From the start I felt more adapted to physics than to something like engineering. To me engineering was a matter of cook books and heavy economic motivations.”
Receiving a teaching assistantship from the University of Illinois, Kusch did graduate work in physics, receiving an M.S. degree in 1933 and a Ph.D. in 1936. His experimental work at Illinois involved optical spectroscopy under the direction of his dissertation adviser, F. Wheeler Loomis, an accomplished physicist in spectroscopic measurements of molecules. Optical spectroscopy was an area of classical physics that emphasized accurate measurements; within this field Kusch pursued a career with a special focus on precision. After obtaining his doctoral degree, Kusch joined the physics department at the University of Minnesota as a research assistant. There he became expert in a sphere of spectroscopic measurement known as mass spectroscopy. Unlike optical spectroscopy, in which atoms or molecules at rest interact with light of various frequencies, the mass spectroscopic technique directs a current of electrically charged atoms or molecules through a strong magnetic field, which causes the charged particles to bend to a greater or lesser degree, depending upon their mass. A detector such as a photographic film permits clear measurement of the particles because of their differences in deflection, even for particles having nearly the same mass—for example, isotopes of the same element.
Upon the recommendation of his Minnesota supervisor to the outstanding physicist 1.1. Rabi (Nobel Prize, 1944), Kusch joined Rabi’s group at Columbia University in New York City as an instructor in 1937. Rabi had pioneered development of the still more advanced spectroscopic method based on magnetic resonance. The essential foundation of this technique is that atomic particles having a spin angular momentum will precess (rotate about an axis as a consequence of external force) in a laboratory magnetic field somewhat analogous to the way a spinning top will precess in the earth’s gravitational field. The precession frequency depends upon the frequency of the imposed oscillating magnetic field and on the spin frequency of the particle. In addition, the method requires the resonant absorption of short-wavelength or very high frequency radio waves that act upon the atomic particle. However, generators with the required radio frequencies and power in the microwave region of the electromagnetic did not exist at the beginning of Kusch’s work at Columbia. The essential devices were developed during World War II by large scientific groups at Massachusetts Institute of Technology, Harvard, Columbia, and elsewhere, in connection with the construction of military radar systems. These wartime activities, although unrelated to fundamental nuclear research, were to make suitable instrumentation available later for Kusch’s advanced postwar discoveries at Columbia.
During the war he spent a part of his time at the Westinghouse Electric Corporation (1941-1942), Columbia (1942-1944), and Bell Telephone Laboratories (1944-1946). The general thrust of his research at each of these locations was the development of improved radio frequency generators of variable high or microwave frequencies.
In 1946 Kusch returned to Columbia University as an associate professor of physics. He was promoted to full professor in 1949 and served as chairman of Columbia’s physics department from 1949 to 1952.
In 1947 Kusch, with the assistance of a graduate student and future colleague, Henry M. Foley, measured the magnetic moment of the electron. This was found to be larger by about one part in 1,000 from the value calculated by the English theoretical physicist Paul A. M. Dirac (Nobel Prize, 1933). Though a very small difference, this important result, coupled with the experimental investigations of Willis E. Lamb, Jr., on the structure of the hydrogen atom (also performed at Columbia University), led to Kusch and Lamb’s sharing the Nobel Prize in physics in 1955.
In addition to his research, Kusch emerged as an exceptional teacher and academic executive. Besides serving as department chairman, Kusch was promoted to academicvice president and provost of the entire university from 1969 to 1972. In 1972 he took a position as professor of physics at the University of Texas in Dallas, where he retired as professor emeritus in 1982. Kusch’s interests extended beyond physics to humanitarian concerns including problems of hunger, the plight of Soviet Jews wishing to emigrate, and the human costs of the Vietnam War.
In 1959 Columbia honored Kusch with its Great Teacher Award. Throughout his career he taught classes to freshmen and sophomore students. He made a point of preparing his undergraduate lectures as carefully as his advanced graduate seminars and his intricate experiments. He also received honorary degrees from eight colleges and universities, including the University of Illinois in 1961 and Columbia University, where he spent the years of his greatest scientific productivity, in 1983.
On 12 August 1935, while a graduate student at the University of Illinois, Kusch married Edith Starr Roberts, with whom he had three daughters. His wife died in 1959. The following year he married Betty Jane Pezzoni, with whom he had two daughters. Kusch suffered a series of strokes and died at his home in Dallas at the age of eightytwo.
The importance of Kusch’s accomplishments was summarized by the presentation speech at the time of the Nobel award: “Your discoveries led to a reevaluation and reshaping of the theory of the interaction of electrons and electromagnetic radiation, thus initiating a development of utmost importance to many of the basic concepts of physics.”
Kusch’s papers include “The Magnetic Moment of the Electron,” Physical Review 74, no. 3 (1948): 250-263, with Henry M. Foley; and “Hyperfine Structure by the Method of Atomic Beams: Properties of Nuclei and of the Electron,” Science 123 (1956). Richard P. Feynman, QED: The Strange Theory of Light and Matter (1985), is a reasonably accessible layperson’s exposition of quantum electrodynamics theory that emerged in large part from the experiments of Kusch, his associates, and others. John S. Rig-den, Rabi: Scientist and Citizen (1987), is a biography of 1.1. Rabi, Kusch’s mentor and senior colleague at Columbia; it furnishes an excellent description of the scientific environment in which Kusch did his Nobel Prize-winning research. An obituary is in the New York Times (23 Mar. 1993).
Leonard R. Solon