Aston, Francis William (1877–1945)

English physicist who developed the mass spectrometer, which separates isotopes by projecting their ions (charged atoms) through a magnetic field. He was awarded the Nobel Prize for Chemistry in 1922 for his contribution to analytic chemistry and the study of atomic theory .

Aston was born and educated in Birmingham. From 1910 he worked in the Cavendish Laboratory, Cambridge, where J J Thomson was investigating positive rays from gaseous discharge tubes. Thomson and Aston examined the effects of electric and magnetic fields on positive rays, showing that the rays were deflected depending on their mass. The deflected rays were made to reveal their positions by aiming them at a photographic plate. The image produced on the photographic plate became known as a mass spectrum, and the instrument itself as a mass spectrometer. This became an essential tool in the study of nuclear physics and later found application in the determination of the structures of organic compounds.

Aston first examined neon gas and found that it consists of two isotopes. Over the next few years he examined the isotopic composition of more than 50 elements, and published Isotopes in 1922.