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It is typically released to the atmosphere in the form of carbon dioxide at BWRs, and methane at PWRs., radioactive carbon dioxide.The gas mixes rapidly and becomes evenly distributed throughout the atmosphere (the mixing timescale in the order of weeks).Libby estimated that the radioactivity of exchangeable carbon-14 would be about 14 disintegrations per minute (dpm) per gram of pure carbon, and this is still used as the activity of the modern radiocarbon standard.In 1960, Libby was awarded the Nobel Prize in chemistry for this work.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.Such deposits often contain trace amounts of carbon-14.These amounts can vary significantly between samples, ranging up to 1% of the ratio found in living organisms, a concentration comparable to an apparent age of 40,000.), or other unknown secondary sources of carbon-14 production.

The resulting neutrons ( but attempts to directly measure the production rate in situ were not very successful.

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. 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.

Carbon-14 can be used as a radioactive tracer in medicine.

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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., 37,000 decays per second). 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.

An age could be estimated by measuring the amount of carbon-14 present in the sample and comparing this against an internationally used reference standard.