Willard Libby (1908–1980), a professor of chemistry at the University of Chicago, began the research that led him to radiocarbon dating in 1945.He was inspired by physicist Serge Korff (1906–1989) of New York University, who in 1939 discovered that neutrons were produced during the bombardment of the atmosphere by cosmic rays.Libby and graduate student Ernest Anderson (1920–2013) calculated the mixing of carbon across these different reservoirs, particularly in the oceans, which constitute the largest reservoir.
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.Dedicated at the University of Chicago on October 10, 2016.In 1946, Willard Libby proposed an innovative method for dating organic materials by measuring their content of carbon-14, a newly discovered radioactive isotope of carbon.To test the technique, Libby’s group applied the anti-coincidence counter to samples whose ages were already known.
Among the first objects tested were samples of redwood and fir trees, the age of which were known by counting their annual growth rings.
Finally, Libby had a method to put his concept into practice. The circular arrangement of Geiger counters (center) detected radiation in samples while the thick metal shields on all sides were designed to reduce background radiation.
The concept of radiocarbon dating relied on the ready assumption that once an organism died, it would be cut off from the carbon cycle, thus creating a time-capsule with a steadily diminishing carbon-14 count.
It showed all of Libby’s results lying within a narrow statistical range of the known ages, thus proving the success of radiocarbon dating.
Top of page The “Curve of Knowns” compared the known age of historical artifacts associated with the Bible, Pompeii, and Egyptian dynasties with their age as determined by radiocarbon dating.
Known as radiocarbon dating, this method provides objective age estimates for carbon-based objects that originated from living organisms.