Isotopes of carbon

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—trace quantities are formed cosmogenically by the reaction ¹⁴N + ¹n → ¹⁴C + ¹H. The most stable artificial radioisotope is ¹¹C, which has 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 relative atomic mass for carbon is 12.0107(8).

Carbon-11

Carbon-11 or ¹¹C is a radioactive isotope of carbon that decays to boron-11. This decay mainly occurs due to positron emission; however, around 0.19–0.23% of the time, it is a result of electron capture. It has a half-life of 20.334 minutes.

Carbon-11 is commonly used as a radioisotope for the radioactive labeling of molecules in positron emission tomography. Among the many molecules used in this context is the radioligand [11C]DASB.