Carbon C-14 is an unstable, radioactive isotope of carbon with an atomic nucleus containing 6 protons and 8 neutrons. Radiocarbon dating is a radiometric dating method that uses (14C) to determine the age of carbonaceous materials up to about 60,000 years old. One of the frequent uses of the technique is to date organic remains from archaeological sites. Carbon-14 can be used as a radioactive tracer in medicine. In the initial variant of the urea breath test, a diagnostic test for Helicobacter pylori, urea labeled with approximately 37 kBq (1.0 μCi) carbon-14 is fed to a patient (i.e., 37,000 decays per second). In the event of a H. 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. The 14C urea breath test has been largely replaced by the 13C urea breath test, which has no radiation issues.