Carbon (6C) has 14 known isotopes, from 8 C to 20 C as well as 22 C , of which 12 C and 13 C are stable. The longest-lived radioisotope is 14 C , with a half-life of 5.70(3)×103 years. This is also the only carbon radioisotope found in nature, as trace quantities are formed cosmogenically by the reaction 14 N + n → 14 C + 1 H . The most stable artificial radioisotope is 11 C , which has a half-life of 20.3402(53) min. All other radioisotopes have half-lives under 20 seconds, most less than 200 milliseconds. The least stable isotope is 8 C , with a half-life of 3.5(1.4)×10−21 s. Light isotopes tend to decay into isotopes of boron and heavy ones tend to decay into isotopes of nitrogen.