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The presence of carbon-14 in the isotopic signature of a sample of carbonaceous material possibly indicates its contamination by biogenic sources or the decay of radioactive material in surrounding geologic strata.
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.
Production rates vary because of changes to the cosmic ray flux caused by the heliospheric modulation (solar wind and solar magnetic field), and due to variations in the Earth's magnetic field.