Radioarbon dating (carbon 14 dating, carbon dating) is a scientific method of calculating the age of carbonaceous material, plant or animal material or objects made from such material that was at one time living. It is accomplished by measuring the amount of carbon 14 (C14 remaining in the material. Carbon 14 is a radioactive isotope that exists in very small amounts in all living animals and plants. While alive, Animalia, Plantae, Fungi, Protista, Archaea and Bacteria normally have about one carbon 14 atom for every trillion carbon atoms. At the moment of death the level of carbon 14 begins to diminish in a predictable and measurable way.
In 1949, Willard Libby at the University of Chicago calculated that it in a gram (0.035 oz. U.S.) of carbon there would be 14 disintegrations per minute in which carbon 14 converted into nitrogen 14. Therefore he reasoned that a sensitive Geiger counter could be used to determine the age of an object. Unfortunately, to obtain an accurate measurement, requires a large sample, which must be incinerated to obtain CO2 gas.
The Shroud of Turin was not a good candidate for Libby’s radiocarbon dating method because a significant part of the Shroud would have been destroyed. But a relatively new method using Accelerator Mass Spectrometry (AMS) permitted testing in 1988 with a very small sample.