Carbon 14

Carbon-14 (or C-14), also known as radiocarbon, is a radioactive isotope of carbon with an atomic nucleus containing 6 protons and 8 neutrons. Its presence in organic materials is the basis of the radiocarbon dating method pioneered by Willard Libby and colleagues (1949) to date archaeological, geological and hydrogeological samples.

Discovery

Carbon-14 was discovered on February 27, 1940, by Martin Kamen and Sam Ruben at the University of California Radiation Laboratory in Berkeley, California. Its existence had been suggested by Franz Kurie in 1934.

Formation

Carbon-14 is produced in the upper layers of the troposphere and the stratosphere by thermal neutrons absorbed by nitrogen atoms. When cosmic rays enter the atmosphere, they undergo various transformations, including the production of neutrons. The resulting neutrons participate in the following reaction:

n + 14N → p + 14C

Decay

The half-life of carbon-14 is 5,730 ± 40 years. Carbon-14 decays into nitrogen-14 through beta decay. A gram of carbon containing 1 atom of carbon-14 per 10^12 atoms will emit ~0.2 beta particles per second. The primary natural source of carbon-14 on Earth is cosmic ray action on nitrogen in the atmosphere, and it is therefore a cosmogenic nuclide.

Applications

The most notable application of carbon-14 is radiocarbon dating. This method allows scientists to date materials that were once part of a living organism. The age of a formerly living organism can be determined by measuring the amount of remaining radiocarbon in it.

See also

• Isotopes of carbon
• Radiocarbon dating
• Radiocarbon year
• Carbon dating
• Carbon cycle