Fluorine-18 was prepared by neutron irradiation of lithium carbonate in the reactor JRR-1. Five grams of lithium carbonate was irradiated for 2hr with a thermal neutron flux of 6×1011 n/cm2/sec. An alumina column was used to separate 18F from the irradiated material. The various factors which affect the separation were studied, and purity and specific activity were determined. About 90 μ c of 18F per gram of lithium carbonate was prepared by this method with a chemical yield exceeding 80%. The prepared 18F was pure enough radiochemically but contained a small amount of lithium and aluminum. The specific activity was about 0.5 mc/mgF. The chemical form of the 18F obtained by the above method was studied by paper-chromatography. A sample was developed on filter paper by the ascending method using butanol-methanol-water mixture as solvent, and the distribution of 18F radioactivity was determined. From the results of the paper-chromatographic study, it was found that most of the 18F existed in the form of flu...