Wiktionary
fluorine-18
n. (context isotope English) An artificial radioactive isotope of fluorine, (nuclide 18 9 F), having nine protons and nine neutrons, that is an important industrial source of positrons
Wikipedia
Fluorine-18
Fluorine-18 (F) is a fluorine radioisotope which is an important source of positrons. It has a mass of 18.0009380(6) u and its half-life is 109.771(20) minutes. It decays by positron emission 97% of the time and electron capture 3% of the time. Both modes of decay yield stable oxygen-18.