Carbon-14
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Carbon-14, 14C, or radiocarbon, is a radioactive isotope of carbon discovered February 27, 1940, by Martin Kamen and Sam Ruben. Its nucleus contains 6 protons and 8 neutrons. Its presence in organic materials is used in radiocarbon dating.
It occurs naturally and has a relative abundance up to 1 part per trillion (0.0000000001%) of all naturally-occurring carbon on Earth. The half-life of carbon-14 is 5730 years. It decays into nitrogen-14 through beta-decay. [1]
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 → 14C + 1H
The highest rate of carbon-14 production takes place at altitudes of 9km to 15km (30,000 to 50,000 feet), and at high geomagnetic latitudes, but the carbon-14 spreads evenly throughout the atmosphere and reacts with oxygen to form radioactive carbon dioxide. Carbon dioxide also permeates the oceans, dissolving in the water.
Carbon-14 can also be produced in ice by fast neutrons causing spallation reactions in oxygen.
Most of man-made chemicals are made of fossil fuels, like petroleum or coal, where the carbon-14 decayed. Presence of carbon-14 in the isotopic signature of a sample of carbonaceous material therefore indicates its possible biogenic origin.
See also
References
Kamen, Martin D. Radiant Science, Dark Politics: A Memoir of the Nuclear Age, Forward by Edwin M. McMillan, Berkeley: University of California Press, 1985.
Template:Chemistry-stubfr:Carbone 14 ja:炭素14 pl:Węgiel-14 pt:Carbono-14 zh:碳14