This Day In History: 1940-02-27

Martin Kamen and Samuel Ruben confirmed the existenceof the carbon isotope 14C. Working at the University of California, Berkeley, CA, USA, they detected radioactivity in a sample of CO2 obtained by burning a graphite target that had been bombarded with deuterons in the lab’s cyclotron. Decaying to 14N through β emission, the isotope has a very long half life (later found to be 5730 years). This opened up new possibilities for using radioactive tracers to elucidate reaction mechanisms. Building on Ruben’s and Kamen’s discovery, Willard Libby and colleagues developed radiocarbon dating in 1949. The age of organic objects can be calculated by comparing the ratio of remaining 14C in a sample to the atmospheric content at the time of death. This method had a tremendous impact on archaeology, as it allows to accurately date artifacts from a large timescale. For this discovery, Libby was awarded the 1960 Nobel Prize in Chemistry.