Design of a Natural Thorium-232 Metal Target for Actinium-225 Development at Iris

Recently targeted alpha therapy (TAT) using Actinium-225 ( ²²⁵ Ac) has been interested due to impressive clinical results. The ²²⁵ Ac radioisotope decays into Bismuth-209 ( ²⁰⁹ Bi) by emitting four alpha and two beta particles with a half-life of 9.9 days, which is appropriate for medical applications. Several research groups reported that ample quantities of ²²⁵ Ac could be produced via spallation of Thorium-232 ( ²³² Th) with energetic protons, having less than 0.1% of Actinium-227 ( ²²⁷ Ac) as a byproduct. In order to reduce the ²²⁷ Ac/ ²²⁵ Ac ratio, IRIS will employ the energy range of 40-70 MeV protons irradiated onto the Th target. The target has the structure of 30 mm diameter and the thickness of 5 mm ThO ₂ encapsulated by 0.5 mm Al foil, which securely sealed the target material. To ensure the stability and safety of thorium targets under high-power beam conditions, a packaging design for the protective Al layer of thorium targets will be adapted with accompanied by detailed mechanical and thermal analyses. Also, an evaluation of the radiation shielding for proton-irradiated thorium target will be presented. This process focuses on protecting personnel and the public by calculating dose rates around the target system and ensuring the dose rates remain below regulatory limits.