Abstract
Thorium carbide to be tested as target material for the production of 225Ac with the ISOL method, was produced via carbothermal reduction of ThO2 nanoparticles by graphite and graphene oxide, respectively. The use of graphene oxide (GO) as carbon source resulted in a reduced reactivity compared to graphite, confirmed by the presence of unreacted ThO2 mainly in the core of the samples. The reacted ThO2 or ThC2–GO showed a faster reactivity in air, mainly observed as ThC2 amorphization. The specific surface area of the ThC2–GO samples was almost doubled compared to ThC2–graphite samples. The effect of these microstructural features was analysed in terms of thermal diffusivity and calculated thermal conductivity that were both reduced in ThC2–GO samples, however the difference with ThC2–graphite samples decreased at increasing temperature. The present study shows that the use of unreduced GO inhibits the solid-state reaction between ThO2 and C; on the other hand, the high reactivity of the ThC2 so produced is expected to be beneficial for the 225Ac production with the ISOL method, affording a high release efficiency. It is expected that the use of reduced GO could represent a good solution for highly efficient ThC2 targets.
Highlights
Thorium carbide to be tested as target material for the production of 225Ac with the ISOL method, was produced via carbothermal reduction of ThO2 nanoparticles by graphite and graphene oxide, respectively
If one considers the actual C/O ratio found in ThCx–graphite and ThCx–graphene oxide (GO) by elemental analysis, the weight loss calculated with the corrected stoichiometry is around 20 ± 1 wt%, this agrees with the experimental values of 19.6 ± 0.1 wt% for ThCx–graphite but is higher than 17.7 ± 1.6 wt% for ThCx–GO
The lower weight loss observed for ThCx–GO indicates incomplete conversion, which could be an effect of increased surfaces or lower reactivity, as shown in the following
Summary
Thorium carbide to be tested as target material for the production of 225Ac with the ISOL method, was produced via carbothermal reduction of ThO2 nanoparticles by graphite and graphene oxide, respectively. The present study shows that the use of unreduced GO inhibits the solid-state reaction between ThO2 and C; on the other hand, the high reactivity of the ThC2 so produced is expected to be beneficial for the 225Ac production with the ISOL method, affording a high release efficiency. Other explored approaches are the use of 226Ra targets bombarded by protons or neutrons[4] and the direct irradiation of 232Th with high-energy protons[5] None of these techniques is free from the necessity of developing several stages of chemical purification to eliminate co-produced and undesired isotopes of actinium and other elements. With the aim of developing new and more efficient production methods, ISOL (Isotope Separation On-Line) facilities are being considered as sources to get high purity 225Ac for research p urposes[2]. The need for optimized targets at the nanoscale level has lately arisen in the ISOL target community; stable porous nanostructures with high specific surface area (SSA) have been associated with increased performance consistency during irradiation, guaranteeing high yields to experimental u sers[12,13]
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