In 1922, de Hevesy co-discovered (with Dirk Coster) the element hafnium (Hf) (Latin Hafnia for "Copenhagen", the home town of Niels Bohr). Mendeleevs 1869 periodic table arranged the chemical elements into a logical system, but a chemical element with 72 protons was missing. Hevesy determined to look for that element on the basis of Bohrs atomic model. The mineralogical museum of Norway and Greenland in Copenhagen furnished the material for the research.  Characteristic X-ray spectra recordings made of the sample indicated that a new element was present. The accepted account has been disputed by Mansel Davies and Eric Scerri who attribute the prediction that element 72 would be a transition element to the chemist Charles Bury.
Supported financially by the Rockefeller Foundation, Hevesy had a very productive year. He developed the X-ray fluorescence analytical method, and discovered the samarium alpha-ray. It was here he began the use of radioactive isotopes in studying the metabolic processes of plants and animals, by tracing chemicals in the body by replacing part of stable isotopes with small quantities of the radioactive isotopes. In 1923, Hevesy published the first study on the use of the naturally radioactive Pb as radioactive tracer to follow the absorption and translocation in the roots, stems and leaves of Vicia faba, also known as the broad bean. Later, in 1943, the work on radioactive tracing would earn Hevesy the Nobel Prize in Chemistry.
In 1924, Hevesy returned to Freiburg as Professor of Physical Chemistry. In 1930, he went to Cornell University, Ithaca as Baker Lecturer. In 1934, after the Nazis came to power in Germany, he returned to Niels Bohr's Institute at the University of Copenhagen. In 1936, he invented Neutron Activation Analysis. In 1943 he fled to Stockholm (Sweden being neutral during the war), where he an associate of the Institute of Research in Organic Chemistry. In 1949 he was elected Franqui Professor in the University of Ghent. In his retirement, he remained an active scientific associate of the University of Stockholm.