What radiocarbon dating be used on
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.
Their results predicted the distribution of carbon-14 across features of the carbon cycle and gave Libby encouragement that radiocarbon dating would be successful.
He reasoned that a state of equilibrium must exist wherein the rate of carbon-14 production was equal to its rate of decay, dating back millennia.
(Fortunately for him, this was later proven to be generally true.) For the second factor, it would be necessary to estimate the overall amount carbon-14 and compare this against all other isotopes of carbon.
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.