When cosmic rays enter the atmosphere, they undergo various transformations, including the production of neutrons.
The highest rate of carbon-14 production takes place at altitudes of 30,000 to 50,000 feet, and at higher geomagnetic latitudes, but the carbon-14 spreads evenly throughout the atmosphere and reacts with oxygen to form carbon dioxide.
Carbon dioxide also permeates the oceans, dissolving in the water.
In 1960, Libby was awarded the Nobel Prize in chemistry for carbon dating.
Carbon has two stable, nonradioactive isotopes: carbon-12 (12C), and carbon-13 (13C).
The AMS technique allows to date samples containing only a few mg of carbon.
For approximate analysis it is assumed that the cosmic ray flux is constant over long periods of time; thus carbon-14 could be assumed to be continuously produced at a constant rate and therefore that the proportion of radioactive to non-radioactive carbon throughout the Earth's atmosphere and surface oceans is constant: ca. For more accurate work, the temporal variation of the cosmic ray flux can be compensated for with calibration curves.If these curves are used, their accuracy and shape will be the limiting factors in the determination of the radiocarbon age range of a given sample.are traditionally made by counting the radioactive decay of individual carbon atoms by gas proportional counting or by Liquid scintillation counting, but this is relatively insensitive and subject to relatively large statistical uncertainties for small samples (below about 1g carbon).If there is little carbon-14 to begin with, a half-life that long means that very few of the atoms will decay while their detection is attempted (4 atoms/s/mole just after death, hence e.g. Sensitivity has since been greatly increased by the use of accelerator-based mass-spectrometric (AMS)techniques, where all the 14C atoms can be counted directly, rather than only those decaying during the counting interval allotted for each analysis.In addition, there are tiny amounts of the unstable isotope carbon-14 (14C) on Earth.Carbon-14 has a half-life of just under 6000 years and would have long ago vanished from Earth were it not for the unremitting cosmic ray impacts on nitrogen in the Earth's atmosphere, which forms more of the isotope.