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EMILIO SEGRE VISUAL ARCHIVES / AMERICAN INSTITUTE OF PHYSICS / SCIENCE PHOTO LIBRARY EMILIO SEGRE VISUAL ARCHIVES / AMERICAN INSTITUTE OF PHYSICS / SCIENCE PHOTO LIBRARY
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Robert Hofstadter (1915-1990), US physicist. Hofstadter invented an improved scintillation counter in 1948, using sodium iodide activated by thallium. He used linearly accelerated electrons scattered by atomic nuclei to study nuclear structure. He found the nuclear charge density was constant but that it fell off rapidly at the suface of the nucleus. The charge distribution was also found to be related to the nuclear mass. Hofstadter also found that neutrons and protons have size and shape; he concluded that they were made of charged shells but that the charges cancelled out in the neutron. He was awarded a share of the 1961 Nobel Prize in Physics.
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