Investigating solid-state reactions in UAl₂-Al dispersions for Mo-99 target fabrication

Molybdenum-99 (Mo-99), the parent isotope of the widely used medical radioisotope technetium-99m (Tc-99m), is primarily produced via neutron irradiation of uranium-containing targets in research reactors. UAl₂-Al dispersions, with UAl₂ particles embedded in an aluminum matrix, are commonly employed for target fabrication. This study employs a new method for investigating the solid-state reactions between UAl₂ and the Al matrix during target fabrication using stepwise isothermal dilatometry (SID). The study focuses on the formation of UAl₃ and UAl₄, which are less dense than UAl₂ and result in material expansion detected by the linear displacement, which relates to reaction conversion. By analyzing the linear expansion data from 560 °C to 630 °C, SID determines apparent activation energies and identifies the D2 diffusion rate model as the best fit, indicating a fast reaction rate along the UAl₂/Al interfaces and highlighting the crucial role of interface diffusion in the process. This information is crucial for optimizing target fabrication and controlling the final composition of Mo-99 targets.