The story of isotopes and mass spectrometry begins with J. J. Thomson who observed aline at mass 22 in the positive ray analysis of neon in 1912. Interestingly, while Thomsonaccepted the existence of isotopes among the radionuclides, he held firmly to the beliefthat stable elements were monoisotopic. In truth, we should credit Aston with thediscovery of isotopes of the stable elements � as he was when awarded the Nobel Prize inChemistry in 1922. Aston chose the exploration of isotopes of the elements as hisprimary research enterprise; and began by creating a new and improved positive rayanalyzer. His competitor and colleague in this enterprise was A. J. Dempster, anexpatriate Canadian at the University of Chicago, who � developing his own massanalyzer � was the first to report the isotopes of several elements, mainly because he didnot feel the need to use gas discharge as the only method of sample ionization. As theimportance of Einstein's classic equation relating energy and mass became more widelyunderstood, the physics community was intent on determining the exact masses andrelative abundance of the isotopes for all of the elements. This was a strong motivator forthe design and construction of mass analyzers capable of ever more precise massdeterminations as well as accurate abundance measurements. Nier joined this group ofphysicists in 1935 when he reported a previously unknown isotope of potassium. BothDempster, Bainbridge and Nier made important contributions to the understanding ofnuclear fission in uranium. While physicists dominated this endeavor, we can credit apetroleum chemist, Meyerson, for prompting the physics community to revisit andcorrect the relative abundance of chlorine isotopes in 1961.

Isotopes: The era of the physicist

246th National Meeting (2013)

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