Carbon-16

Carbon-16

Carbon (C) has 15 known isotopes, from 8C to 22C, 2 of which (12C and 13C) are stable. The longest-lived radioisotope is 14C with a half-life of 5,700 years. This is also the only carbon radioisotope found in nature, where trace quantities are formed cosmogenically by the reaction 14N + 1n -> 14C + 1H. The most stable artificial radioisotope is 11C, with a half-life of 20.334 minutes. All other radioisotopes have half-lives under 20 seconds, most less than 200 milliseconds. The least stable isotope is 8C, with a half-life of 2.0 x 10−21 s. Averaging over natural abundances, the standard atomic mass for Carbon is 12.0107(8) u.