American physicist Robert Hofstadter, was the joint winner of the 1961 Nobel Prize in Physics (together with Rudolf Mössbauer) for his pioneering studies of electron scattering in atomic nuclei and for his consequent discoveries concerning the structure of nucleons.
Hofstadter was born in a Jewish family in New York City on February 5, 1915. He attended elementary and high schools in New York City and entered City College of New York. In 1935, at the age of 20 graduated with a B.S. degree magna cum laude. Awarded the Kenyon Prize in Mathematics and Physics. Also received a Charles A. Coffin Foundation Fellowship from the General Electric Company, which had enabled him to attend graduate school at Princeton University, where he got his M.S. and Ph.D. degrees at the age of 23. He did his post-doctoral research at the University of Pennsylvania and was an assistant professor at Princeton before joining Stanford University. From 1950 to 1985, Hofstadter taught at Stanford.
In 1948 Hofstadter filed a patent on “Thallium activated Sodium Iodide gamma ray detector” for the detection of ionizing radiation by this crystal. This detector is widely used for gamma ray detection to this day. Hofstadter coined the term fermi (unit), symbol fm, in honour of the Italian physicist Enrico Fermi (1901–1954), one of the founders of nuclear physics, in Hofstadter’s paper “Electron Scattering and Nuclear Structure“, published in 1956 in the Reviews of Modern Physics journal. This term is widely used by nuclear and particle physicists.
In his last few years, Hofstadter became interested in astrophysics and applied his knowledge of scintillators to the design of the EGRET gamma-ray telescope of the Compton Gamma Ray Observatory named for fellow Nobel Laureate in Physics (1927), Arthur Holly Compton. Stanford University’s Department of Physics credits Hofstadter with being “one of the principal scientists who developed the Compton Observatory.
At Stanford he used a linear electron accelerator to measure and explore the constituents of atomic nuclei – protons, neutrons, and electrons .They were all thought to be structure less particles; Hofstadter discovered that protons and neutrons have a definite size and form. He was able to determine the precise size of the proton and neutron and provide the first reasonably consistent picture of the structure of the atomic nucleus. He found that both the proton and neutron have a central, positively charged core surrounded by a double cloud of pi-mesons. Both clouds are positively charged in the proton, but in the neutron the inner cloud is negatively charged, thus giving a net zero charge for the entire particle. In 1961, Hofstadter has received Nobel Prize in Physics, along with Rudolf Mössbauer, for the pioneering studies of electron scattering in atomic nuclei.