Radiolysis reduction in liquid solution targets for the production of ⁸⁹Zr

Increased interest in radiometals for nuclear medicine and imaging can be hampered by radionuclide supply. ⁸⁹Zr for example, is a PET imaging nuclide for which no radionuclide generator exists. One method to produce ⁸⁹Zr involves irradiating aqueous solutions of yttrium nitrate salt on small medical cyclotrons. However, in irradiating these solutions the radiolysis of water can cause significant H₂ and O₂ gas buildup, which can eventually rupture a sealed target vessel. We examine the role of nitrate and nitrite in radiolysis. Here, we find that using copper-coated cadmium pellets to chemically reduce nitrate to nitrite in solution prior to irradiation can reduce in-target radiolysis by approximately 60% as compared to other published methods of radiolysis reduction, but only in acidic solutions. We hypothesize that during irradiation, nitrate is converted to nitrite, consuming free radicals which would otherwise be available to eliminate molecular gas species. Performing this conversion before irradiation may limit the consumption of these beneficial free radicals.