Bloch, Felix b. October 23, 1905; Zurich, Switzerland d. September 10, 1983; Zurich, Switzerland
A Swiss physicist who left Germany for the United States in the early 1930s and participated in the Manhattan Project, Felix Bloch was a pioneer of solid-state physics and was awarded the Nobel Prize for his research on magnetic nuclear resonance.
Bloch studied engineering at the Eid- genossische Technische Hochschule (Federal Institute of Technology, ETH) in Zurich. Impressed by Peter Debye’s lectures, he decided to switch from engineering to physics and mathematics. After he received his diploma in 1926, Bloch became the first doctoral student of Werner Heisenberg at the University of Leipzig. In his dissertation (1928), Bloch investigated the conductivity of metals by applying the new methods of quantum theory. He constructed Eigenfunctions of electrons in the periodic lattice potential that became fundamental to the theory of solid-state physics, later known as “Bloch Waves.” After some time as an assistant to Wolfgang Pauli in Zurich, where supraconductivity had been his research topic, and a fellowship at the University of Utrecht, Bloch returned to Leipzig in 1930. Two years later, he defended his second doctoral dissertation (Habilitation). During this time, Bloch collaborated with Niels Bohr in Copenhagen and worked on the theory of ferromagnetica, as well as on metallic conductivity. When the National Socialist German Worker’s Party (NSDAP) came to power in Germany, he resigned voluntarily from his teaching position at the University of Leipzig.
Financed by a grant from the Rockefeller Foundation, Bloch continued his research in Rome and Cambridge. A recommendation from Bohr got Bloch a two-year appointment at Stanford University. When he turned down an offer to join the Hebrew University in Jerusalem in 1936, Bloch was made full professor at Stanford. He thus became the first professor of theoretical physics at that university.
Yet Bloch did not remain a classical theoretical physicist. He favored a close connection between theoretical and experimental physics. Bloch performed experiments using an X-ray tube to produce neutrons and developed a theory of magnetic neutron scattering. From 1938 onward, he collaborated with Luis Alvarez from the University of California at Berkeley, where he had access to a cyclotron. Using this apparatus, Bloch and Alvarez determined the magnetic moment of the neutron. Bloch managed to convince Stanford to acquire a cyclotron. It was constructed from 1939 to 1941, mainly for the purpose of providing neutrons for magnetic investigations. For the Manhattan Project, Bloch determined the energy spectrum of those neutrons that were set free in the process of nuclear fission. For a few months in 1943, he worked on the implosion problem in Los Alamos. Afterward he joined the Radio Research Laboratory at Harvard University, where he worked on technologies that could prevent detection of any military objects like ships or airplanes by radar.After the end of World War II, Bloch returned to Stanford University. Through his research on ferromagnetism and magnetic moments, he became interested in nuclear induction. Bloch was able to determine the nuclear moments of solid bodies, fluids, and gases by measuring the “Larmor frequency” of an external alternating magnetic field. The method was called nuclear magnetic resonance (NMR) and became important in chemistry, biology, and medicine. Bloch, together with Edward Purcell, was awarded the Nobel Prize for this discovery in 1952. From 1954 to 1955 Bloch served as the general manager of the newly founded Conseil Europeen pour la Recherche Nucleaire in Geneva.
Back at Stanford University, he devoted much of his time to the construction of a large linear accelerator. Continuing his research on nuclear induction, he focused on the microscopic interpretation of phenomenological parameters. During the 1960s, Bloch returned to the topic of supraconductivity. He found a comparatively simple explanation for the “Josephson effect” (a flow of electric current between two pieces of superconducting material separated by a thin layer of insulating material). Bloch continued his research until his death during a visit in Zurich.
Stefan L. Wolff
See also U.S.-German Intellectual Exchange
References and Further Reading
Chodorow, Marvin, ed. Felix Bloch and Twentieth-Century Physics. Houston: William Marsh Rice University, 1980.
Hofstadter, Robert. Felix Bloch: Biographical Memoirs of the National Academy of Sciences 64 (1994): 34-71.