Its existence had been suggested by Franz Kurie in 1934. 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.
Small amounts of carbon-14 are not easily detected by typical Geiger–Müller (G-M) detectors; it is estimated that G-M detectors will not normally detect contamination of less than about 100,000 disintegrations per minute (0.05 µCi).
Liquid scintillation counting is the preferred method.
The gas mixes rapidly and becomes evenly distributed throughout the atmosphere (the mixing timescale in the order of weeks).
Carbon dioxide also dissolves in water and thus permeates the oceans, but at a slower rate.
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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.
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