Design and simulation of a thorium target for 225Ac production

There is growing interest in finding new sources of 225Ac, an isotope with potential use in the treatment of metastatic disease. Proposed production alternatives include the proton irradiation of thorium above 100 MeV, however, concerns exist about the co-production of the long-lived and toxic 227Ac. This work describes the design and simulated yields for a thorium target that will be irradiated at TRIUMF, and also proposes a post-irradiation chemical isolation procedure that produces two separate 225Ac products: the first by direct production from the irradiation, and the second from the isolation of Ra isotopes that form a generator of 225Ac. FLUKA simulations combined with models of the proposed chemical isolation procedures suggest that a 1130 µA·hr irradiation at 90 µA of a target containing 1 g of thorium will directly produce 42.2 MBq of 225Ac with 0.08 MBq of 227Ac. The generator-produced 225Ac fraction will contain less activity of higher purity: 2.2 MBq of 225Ac and <1Bq of 227Ac.