¹⁴C, an isotope of carbon-12 (¹²C). ¹⁴C contains two more neutrons and is radioactive and used in carbon dating. While carbon-12 is not radioactive, the half life of ¹⁴C is 5730 years. This relatively short half life allows the ratio of carbon-12 to carbon-14 to be used to date objects containing carbon to an age of 50,000 years before present time.