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

Abstract

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.