the isotopic carbon atom that comprises 99 percent of naturally occurring carbon, and that since 1961 has been used as the standard for atomic weight by representing a unit of 12.00000.
Also car·bon-12 [kahr-buh n-twelv] /ˈkɑr bənˈtwɛlv/.
Origin of carbon 12
First recorded in 1940–45
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019
A stable isotope of carbon, having six protons and six neutrons in the nucleus. Carbon 12 makes up most naturally occurring carbon.
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