However, open-air nuclear testing between 1955–1980 contributed to this pool.
A calculation or (more accurately) a direct comparison of carbon-14 levels in a sample, with tree ring or cave-deposit carbon-14 levels of a known age, then gives the wood or animal sample age-since-formation.Carbon-14 is produced in the upper layers of the troposphere and the stratosphere by thermal neutrons absorbed by nitrogen atoms.Carbon-14 was discovered on 27 February 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. 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.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.
This is small compared to the doses from potassium-40 (0.39 m Sv/year) and radon (variable).
Carbon-14 can be used as a radioactive tracer in medicine. pylori infection, the bacterial urease enzyme breaks down the urea into ammonia and radioactively-labeled carbon dioxide, which can be detected by low-level counting of the patient's breath.
Atmospheric nuclear weapon tests almost doubled the concentration of The above-ground nuclear tests that occurred in several countries between 19 (see nuclear test list) dramatically increased the amount of carbon-14 in the atmosphere and subsequently in the biosphere; after the tests ended, the atmospheric concentration of the isotope began to decrease.
One side-effect of the change in atmospheric carbon-14 is that this has enabled some options (e.g.
In the initial variant of the urea breath test, a diagnostic test for Helicobacter pylori, urea labeled with approximately 37 k Bq (1.0 µCi) carbon-14 is fed to a patient (i.e.