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At the time, no radiation-detecting instrument (such as a Geiger counter) was sensitive enough to detect the small amount of carbon-14 that Libby’s experiments required.Libby reached out to Aristid von Grosse (1905–1985) of the Houdry Process Corporation who was able to provide a methane sample that had been enriched in carbon-14 and which could be detected by existing tools.In a system where carbon-14 is readily exchanged throughout the cycle, the ratio of carbon-14 to other carbon isotopes should be the same in a living organism as in the atmosphere.However, the rates of movement of carbon throughout the cycle were not then known.But no one had yet detected carbon-14 in nature— at this point, Korff and Libby’s predictions about radiocarbon were entirely theoretical.In order to prove his concept of radiocarbon dating, Libby needed to confirm the existence of natural carbon-14, a major challenge given the tools then available.Korff predicted that the reaction between these neutrons and nitrogen-14, which predominates in the atmosphere, would produce carbon-14, also called radiocarbon.Libby cleverly realized that carbon-14 in the atmosphere would find its way into living matter, which would thus be tagged with the radioactive isotope.

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We learned rather abruptly that these numbers, these ancient ages, are not known accurately; in fact, it is at about the time of the First Dynasty in Egypt that the first historical date of any real certainty has been established.” —Willard Libby, Nobel Lecture, 12 December 1960 The concept of radiocarbon dating focused on measuring the carbon content of discreet organic objects, but in order to prove the idea Libby would have to understand the earth’s carbon system.

Using this sample and an ordinary Geiger counter, Libby and Anderson established the existence of naturally occurring carbon-14, matching the concentration predicted by Korff. Fortunately, Libby’s group developed an alternative. They surrounded the sample chamber with a system of Geiger counters that were calibrated to detect and eliminate the background radiation that exists throughout the environment.

The assembly was called an “anti-coincidence counter.” When it was combined with a thick shield that further reduced background radiation and a novel method for reducing samples to pure carbon for testing, the system proved to be suitably sensitive.

Top of page Carbon-14 was first discovered in 1940 by Martin Kamen (1913–2002) and Samuel Ruben (1913–1943), who created it artificially using a cyclotron accelerator at the University of California Radiation Laboratory in Berkeley.

Further research by Libby and others established its half-life as 5,568 years (later revised to 5,730 ± 40 years), providing another essential factor in Libby’s concept.

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