Feasibility of producing 225Ac via thermal neutron irradiation of 226Ra: A systematic theoretical study

With a suitable half-life and abundant radiolabeling strategy, 225Ac has become one of the most promising radionuclides in the area of targeted alpha therapy. However, limited radionuclide supply is threatening the development of 225Ac related endoradiotherapy dramatically. As the parent nuclide of 225Ac, 229Th can be produced via 226Ra(3n, 2β)229Th reaction in a nuclear reactor. However, related practice has not been conducted in large scale, since the nuclear reaction pathway for producing 229Th is complicated. In this work, the feasibility of producing 225Ac/229Th in a reactor was confirmed by systematic theoretical calculations, and a procedure that combines irradiation with separation process was proposed. The results show that 176 MBq of 229Th can be produced by irradiating 1.0 g of 226Ra with a neutron flux density of 1 × 1015 n cm−2 s−1 for 90 days. This will generate 150 MBq of 225Ac monthly from a radionuclide generator, which is sufficient for the single treatment cycle of 200 patients each year considering the radioactivity loss in radiochemical separation, transfer and radiolabeling process. In addition, this irradiation process will also produce 37.8 GBq 227Ac for the preparation of 227Ac-227Th-223Ra generator. In general, the production of 225Ac by neutron irradiation of 226Ra in reactor is practicable and holds potential to alleviate the shortage of current supply of 225Ac.