Production of 225Ac for medical application from 232Th-metallic targets in Nb-shells irradiated with middle-energy protons

A method for high-scale Ac-225-production for medical application from a massive metallic Th-232-target irradiated with 160 MeV-protons is described. The target was made of a metallic Th disk of few mm thickness encapsulated in Nb shell using diffusion welding that provided effective target cooling under an intensive proton beam. Chemical processing started with selectively dissolving Nb and Th in mixtures of HF and HNO3 of different concentrations. The further chemical treatment included two sequential extractions of Th(iv) with di(2-ethylhexyl)orthophoshoric acid (HDEHP) and purification of Ac by extraction chromatography with DGA-, LN- and TRU-resins. The "end-to-start" technique, where the eluate of the column filled with one sorbent serves as the eluent for the column with next sorbent, was realized. The achieved total chemical yield of Ac-225 was 87% and radionuclidic purity was better than 99.8% (excepting 0.1-0.2% Ac-227 generated at the end of irradiation). The presented method can provide a hundred GBq of Ac-225 in one irradiation run.