The Nobel Prize in Physics 1961
The Nobel Prize in Physics 1961 was divided equally between Robert Hofstadter "for his pioneering studies of electron scattering in atomic nuclei and for his thereby achieved discoveries concerning the structure of the nucleons" and Rudolf Ludwig Mössbauer "for his research concerning the resonance absorption of gamma radiation and his discovery in this connection of the effect which bears his name."
Matter is composed of atoms with small nuclei surrounded by electrons. Robert Hofstadter developed apparatus for studying nuclei’s internal structure. A high-energy electron beam from an accelerator was directed towards nuclei and by examining the scattering of the electrons, he could investigate how charges were distributed. He could also investigate how the magnetic moment within the nuclei’s protons and neutrons was distributed. Nuclei were thereby proven not to be homogeneous, but to have internal structures.
[Curator’s note: The following material quotes and paraphrases extensively from articles posted by the Nobel Prize Committee and the Princeton Herald and the Princeton Alumni Weekly; see Sources below for details.]
Robert Hofstadter was born in New York, N.Y., of parents Louis Hofstadter and Henrietta Koenigsberg, on February 5, 1915.
Hofstadter attended elementary and high schools in New York City and graduated in 1935 from the College of the City of New York with the B.S. degree, magna cum laude.
On graduation from college Hofstadter received the Kenyon Prize in Mathematics and Physics, and later the Coffin Fellowship, awarded by the General Electric Company.
Princeton for Graduate Work, UPenn instructor, National Bureau of Standards
Hofstadter went to graduate school at Princeton University where he studied physics from 1935 – 1938 and received both the M.A. and Ph.D. degrees in 1938. While at Princeton, he was a research assistant, a junior fellow and during his third and last year, a Proctor fellow.
His dissertation was entitled: “Infra-red Absorption by Light and Heavy Formic and Acetic Acids, with Special Regard to the Problems of the Hydrogen Bond.” His Ph.D. work was concerned with infrared spectra of simple organic molecules and, in particular, with the partial elucidation of the structure of the well-known “hydrogen bond”.
In 1938 – 1939, as a Proctor Fellow for postdoctoral work, he began a study of photoconductivity in willemite crystals. This work led to the discovery, with R. Herman, of the warm-up dark currents which demonstrated the existence of trapping states in crystals.
He carried out research on crystal conduction counters, on the Compton effect, and on scintillation counters. In 1948 he discovered that sodium iodide, activated by thallium, made an excellent scintillation counter. In 1950, with J. A. McIntyre, he found that well-formed crystals of this material provided remarkable energy-measuring devices for gamma rays and energetic particles and thus could be used as spectrometers in addition to gamma-ray and particle counters of high efficiency.
According to Dr. Walker Bleakney, chairman of the department, his interests were extraordinarily varied, covering diverse fields. Dr. Bleakney taught Dr. Hofstadter and was associated with him in the laboratories, as was the case with Professor Eugene Paul Wigner, and others still in the department. In 1939 Hofstadter received the Harrison Fellowship at the University of Pennsylvania where he helped to construct a large Van de Graaff machine for nuclear research. At Pennsylvania he first met L. I. Schiff, who has been a friend and colleague for many years.
He was an instructor in physics and a Harrison fellow at the University of Pennsylvania for the next few years, except for one term in 1941 as an instructor in physics at City College. During the war years Hofstadter worked first at the National Bureau of Standards and later at the Norden Laboratory Corporation. He left industry at the end of the war to become Assistant Professor of Physics at Princeton University.
Stanford University Professor
In 1950 Hofstadter left Princeton to become Associate Professor of Physics at Stanford University where he initiated a program on the scattering of energetic electrons from the linear accelerator, invented by W. W. Hansen, which was then under construction. While building equipment for the electron-scattering experiments, he continued working on scintillation counters and developed new detectors for neutrons and X-rays. High-speed inorganic (CsF) and useful Cerenkov (TlCl) counters were discovered at Stanford. Other studies carried out in the early years at Stanford were concerned with cosmic rays and with cascade showers generated by high-speed electrons.
After 1953 electron-scattering measurements became Hofstadter’s principal interest. With students and colleagues, he investigated the charge distribution in atomic nuclei and afterwards the charge and magnetic moment distributions in the proton and neutron. The electron-scattering method was used to find the size and surface thickness parameters of nuclei. Many of the principal results on the proton and neutron were obtained in the years 1954-1957. Since 1957 emphasis in the research program has been placed on making more precise studies of the nucleon form factors. He received the Nobel Prize in 1961.
Hofstadter was elected to the National Academy of Sciences (U.S.A.) in 1958 and was named California Scientist of the Year in 1959. He has also been a Guggenheim Fellow (1958 – 1959) and spent one year at CERN in Geneva, Switzerland, on sabbatical leave.
Robert Hofstadter died on November 17, 1990.