<Tr> <Td_colspan="2"> Complete table of nuclides </Td> </Tr> <P> Carbon - 14, C, or 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 . 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 . </P> <P> There are three naturally occurring isotopes of carbon on Earth: 99% of the carbon is carbon - 12, 1% is carbon - 13, and carbon - 14 occurs in trace amounts, i.e., making up about 1 or 1.5 atoms per 10 atoms of the carbon in the atmosphere . Carbon - 12 and carbon - 13 are both stable, while 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 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 . However, open - air nuclear testing between 1955--1980 contributed to this pool . </P> <P> The different isotopes of carbon do not differ appreciably in their chemical properties . This resemblance is used in chemical and biological research, in a technique called carbon labeling: carbon - 14 atoms can be used to replace nonradioactive carbon, in order to trace chemical and biochemical reactions involving carbon atoms from any given organic compound . </P>

What is the ratio of c14 to c12
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