Cryogenic target design considerations for the production of [18F]fluoride from enriched [18O]carbon dioxide

Four cryogenic target designs are described for the production of fluorine-18 in the chemical form of fluoride using oxygen-18-enriched carbon dioxide gas utilizing the (18)O(p,n)18F nuclear reaction. The targets are conical in shape and made of copper or silver and the carbon dioxide is frozen into the cone at liquid nitrogen temperatures. Three of the targets (2 copper and 1 silver) have four cooling fins extending radially and are different lengths, and one target has only a single heat sink at the rear of the cone. The targets with four cooling fins could be run with 17.4 MeV protons incident on the target material at a beam current of 25 microA with no detectable volatilization of the target material, although yields did decrease slightly when compared with lower current runs. The target with the single cooling block showed volatilization at about 8 microA. The two copper targets of different lengths did not show a difference in the volatilization of the target material at the beam current limit of our cyclotron (25 microA). The shorter target did maintain production with a lower amount of gas frozen into the target, while the longer target maintained production at higher beam currents. Targets of this type are compatible with low energy, high current accelerators because very thin windows may be used.