Fluorine-18 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) min

Flourine-18 is an important isotope in the radiopharmaceutical industry, and is primarily synthesized into FDG for use in Positron Emission Tomography (PET Scans). It is subsitituted for Hydrogen and used a tracer in the scan. Its significance is due to both its short half-life and the emission of positrons when decaying (PET being Positron Emission tomography). In the radiopharmaceutical industry, it is made using either a cyclotron or linear particle accelerator by bombarding oxygen-18 with hydrogen ions.