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In 1939, as political tensions in Europe increased, American physicists learned of an astonishing discovery: the nucleus of the uranium atom can be split, causing the release of an immense amount of energy. Given the prospects of oncoming war, the discovery was just as worrying as it was intellectually exciting. Could the Germans use it to develop an atomic bomb?
The Americans realized that they had to determine whether a bomb was physically possible. Theoreticians predicted that it was the nuclei of the rare U-235 isotope that undergo fission, the more common U-238 being inactive.
Alfred Nier, a young physicist at the University of Minnesota, was one of the few people in the world with the expertise to separate the isotopes. He built this mass spectrograph in February 1940 for that specific purpose. It has two small metal plates, each for collecting a tiny sample of one of the isotopes. They were tested: the fission prediction was correct. Nier remarked, "These experiments emphasize the importance of uranium isotope separation on a larger scale for the investigation of chain reaction possibilities in uranium." Soon, the Manhattan Project was in full swing, expending enormous resources to do just that.
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Object ID: 1990.0446.01
Division: Division of Medicine and Science
Subject(s): Energy & Power, Measuring & Mapping, Military
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