Francis William Aston, English chemical physicist, c 1920s.
© Science Museum / Science & Society Picture Library
Francis William Aston, (1877-1945) worked with J J Thomson (1856-1940) at Cambridge University. In 1919 he devised a mas spectrograph which was able to separate atoms of similar mas. With it he showed that not all atoms in a chemical element are identical. Aston identified the isotopes of over 50 elements. He was awarded the Nobel Prize for Chemistry in 1922.