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Portrait of Francis Aston (1877-1945), British physicist and Nobel Laureate. After WW1, Aston helped Thomson in his studies of the deflection of ions in magnetic fields. He went on to improve Thomson's apparatus, designing it so as to make all atoms of a given mass fall on the same part of a photographic plate. Working with neon, he found that two lines were observed, indicating the presence of two isotopes. He repeated this with chlorine with similar results. The device, called the mass spectrometer, showed that most stable elements had isotopes. His work earned him the 1922 Nobel Prize for Chemistry, and introduced a powerful new analytical tool to science.
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