Monte Carlo Simulation of Medical Isotopes Production by Irradiation of nat U and ²³² Th Targets with P, α, ⁹ Be and ¹² C

Advances in nuclear technology and modern medicine have driven the development of a variety of radiopharmaceuticals, labeled with medical isotopes, that play an important role in the treatment and diagnosis of various diseases. With the decommissioning of high-flux nuclear reactors, high-energy proton-induced spallation reactions on thorium are now becoming an alternative and the most commonly used method for large-scale production of isotopes such as 225Ac and 227Th.However, investigations into isotopes produced by irradiating thorium and uranium targets with other types of particles remains relatively limited. Additionally, the thickness of the conventional 232Th targets used for isotope production is significantly less than the proton range, resulting in the underutilization of a large portion of the proton beam.This study aims to identify the most effective incident projectile and materials for the production of 225Ac, 223Ra, 225Ra, 227Th, and 99Mo via the bombardment of the thick target with accelerated protons, α-particles, 9Be, and 12C to increase the supply of 225Ac or other medical isotopes.This work considers a water-cooled spallation target that consists of a mixture of heavy water and thorium metal particles (232Th + D2O) or uranium metal particles (natU + D2O). This design not only addresses the heat dissipation issue of the target material, but also simultaneously enhances the isotope yield. The Monte Carlo transport code PHITS (particle and heavy ion transport code system) was employed to calculate and compare the effects of the different beam energies, types of incident projectiles, and target materials on the isotope yields, secondary particle flux distributions, and energy deposition.The predictions indicate that, compared to the widely investigated proton bombardment schemes on thorium targets in existing studies, irradiation with 9Be achieves the highest isotope yields, as it facilitates the production of more high-flux neutrons or other secondary particles to drive isotope breeding, but it also leads to increased energy deposition. Moreover, under identical incident particle conditions, thorium targets generally exhibit a higher isotopic yield than uranium targets, while also demonstrating lower energy deposition, making them more efficient for isotope production.In conclusion, when adopting a water-cooled spallation target, 9Be bombardment of a thorium target is more likely to achieve higher efficiency in isotope production within a relatively short irradiation time.