Wiktionary
n. (context isotope English) A minor stable isotope of oxygen, (nuclide 18 8 O), having eight protons and ten neutrons; it amounts to about 0.2% of the element in nature
Wikipedia
Oxygen-18 () is a natural, stable isotope of oxygen and one of the environmental isotopes.
is an important precursor for the production of fluorodeoxyglucose (FDG) used in positron emission tomography (PET). Generally, in the radiopharmaceutical industry, enriched water is bombarded with hydrogen ions in either a cyclotron or linear accelerator, creating fluorine-18. This is then synthesized into FDG and injected into a patient. It can also be used to make an extremely heavy version of water when combined with tritium ( hydrogen-3): or . This compound has a density almost 30% greater than that of natural water
Usage examples of "oxygen-18".
This model fits observations deduced from the amount of oxygen-18 (a radioactive isotope of oxygen) in geological deposits.