Spark plasma sintering in manufacturing and recycling of ZnO targets for medical radioisotopes cyclotron-based production

This work reports on the successful use of the Spark Plasma Sintering (SPS) process for the densification of the zinc oxide (ZnO) powder (<5 μm size) to manufacture solid thick targets for cyclotron-based production of radionuclides. The complete technological cycle for ZnO pellet sintering and its adhesion to the metallic backing to create a coin-shaped target structure is discussed. Different technological approaches were demonstrated, including sintering in series and parallel. To investigate the structural changes that occur during the rapid densification process, SEM and XRD analyses were performed on ZnO powder and pellets. The metallurgical interface analysis was carried out on the final target to acknowledge the adhesion quality between the different materials (metals and ceramics). The thermomechanical stability of targets was tested under different proton beam irradiation currents at the solid target station of a medical cyclotron. All the experiments were performed with natural ZnO powder to demonstrate the reproducibility of the results (relative densities higher than 95 % and low material losses of 2.5 ± 1.9 %, n = 49). This would ensure in the future that enriched [70Zn]ZnO material can be used to produce pure copper-67 (67Cu) radionuclide through cyclotron irradiation. Furthermore, a strategy for the chemical recovery of ZnO pellets into their original powder form after dissolution was studied. The recovery yield of ZnO achieved an average of 84.9 ± 4.7 % (n = 15). This result demonstrates the efficacy of the optimised precipitation method with NaOH. The recovered powder was successfully reused for the manufacture of a new target.