text: Fluorine-18 is usually produced by irradiation of O-enriched water (HO) with high-energy (about 18 MeV) protons prepared in a cyclotron or a linear accelerator, yielding an aqueous solution of F fluoride. This solution is then used for rapid synthesis of a labeled molecule, often with the fluorine atom replacing a hydroxyl group. The labeled molecules or radiopharmaceuticals have to be synthesized after the radiofluorine is prepared, as the high energy proton radiation would destroy the molecules.
  Large amounts of oxygen-18 enriched water are used in positron emission tomography centers, for on-site production of F-labeled fludeoxyglucose (FDG).
  An example of the production cycle is a 90-minute irradiation of 2 milliliters of O-enriched water in a titanium cell, through a 25 μm thick window made of Havar (a cobalt alloy) foil, with a proton beam having an energy of 17.5 MeV and a beam current of 30 microamperes.
  The irradiated water has to be purified before another irradiation, to remove organic contaminants, traces of tritium produced by a O(p,t)O reaction, and ions leached from the target cell and sputtered from the Havar foil.