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a chemical element, atomic number 6, atomic weight 12.011. (See Appendix 6.)
carbon 11 a radioactive isotope of carbon, atomic mass 11, having a half-life of 20.39 minutes; used as a tracer in positron emission tomography.
carbon 14 a radioactive isotope of carbon, atomic mass 14, having a half-life of 5730 years; used as a tracer in cancer and metabolic research.
car·bon 11 (11C),(kar'bŏn),
A cyclotron-produced, positron-emitting radioisotope of carbon with a half-life of 20.3 minutes; used in positron emission tomography (PET).