Preparation and characterization of molybdenum solid targets for high current cyclotron production of medical ⁹⁹mTc radionuclides

^99mTc is widely used in modern nuclear medicine and is currently obtained from the radioactive decay of ⁹⁹Mo produced by bombarding highly enriched ²³⁵U with neutrons in a nuclear reactor. The unplanned outages of the reactors cause ⁹⁹Mo shortages at the global level, so research studies for alternative methods to produce ^99mTc are ongoing all over the world. The cyclotron ¹⁰⁰Mo(p, 2n) ^99mTcapproach via nuclear reaction was found to be the most promising one. The key challenge for the large-scale cyclotron production of ^99mTc consists in the development of high-density ¹⁰⁰Mo targets that are: able to support multi-hour high current cyclotron irradiation, with high density, adhesion to baseplate, and high thickness, without material losses. An "ideal" technique, to fulfill all the requirements for the target, does not exist [1-5]. The choice of target preparation technique is always a compromise between fulfilling the application's particular requirements and the cost of implementation, so extended research is needed. In this context, the main objective of this study consists in research for the development and testing of robust molybdenum solid targets to be further used for high current cyclotron production of ^99mTc radionuclide using the ¹⁰⁰Mo(p,2n) nuclear reaction. The cyclotron target should be highly bonded to a metallic baseplate and be able to sustain high cyclotron currents. For this purpose, a new approach to obtain a high-density molybdenum target using pressing-heating process was developed by making use of the scanning capability of the electron-gun part of the high vacuum deposition system, allowing the complete surface heating without inducing deformations, in high vacuum (without impurities), without the evaporation process (no material losses). The surface morphology, roughness, hardness, impurities, adhesion performances were established by using Atomic Force Microscopy (AFM), Scanning Electron Microscopy (SEM) and Energy-Dispersive X-Ray Spectroscopy (EDX) techniques. The prepared targets were also successfully irradiated with protons at high-current cyclotron. (author)