What is the name of the carbon isotope used in radiocarbon dating?

The carbon isotope used in radiocarbon dating is Carbon-14, also written as carbon-14, C-14, or ¹⁴C.

Carbon-14 is radioactive, unlike the stable carbon isotopes Carbon-12 and Carbon-13. Cosmic rays help create it in the upper atmosphere when neutrons interact with nitrogen-14. The resulting carbon-14 becomes part of atmospheric carbon dioxide, which plants absorb during photosynthesis. Animals acquire it through their food.

When an organism dies, it stops exchanging carbon with its environment. The carbon-14 already present in its tissues then gradually decays into nitrogen-14. Because this decay follows a predictable rate, scientists can estimate when the organism stopped living by measuring how much carbon-14 remains.

Carbon-14 has a half-life of roughly 5,700 years, so radiocarbon dating is especially useful for organic materials up to about 50,000–60,000 years old. Carbon-12 and Carbon-13 are common mix-ups: they are carbon isotopes, but they are not radioactive and cannot provide the decay signal used by this method. Radiocarbon dates are also calibrated because atmospheric carbon-14 levels have varied over time.