carbon 12

noun

1. 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.

carbon 12

1. A stable isotope of carbon, having six protons and six neutrons in the nucleus. Carbon 12 makes up most naturally occurring carbon.

Word History and Origins

Origin of carbon 12¹

First recorded in 1940–45