Ac-225 and Pb-212 production at TRIUMF via proton-spallation of thorium metal
Andrew Kyle Henderson Robertson, Hua Yang, Stefan Zeisler, Valery Radchenko, Cornelia Hoehr, and Paul Schaffer
Life Sciences De
Oral Presentation
The authors have no conflicts of interest.
TRIUMF has begun production of Ac-225 by the irradiation of thorium metal with 480 MeV protons and has developed new methods for separating Ac from these targets. The first target received 85 uA for a total of 31 hours, producing 11.7 mCi of Ac-225 and 2.1 mCi of parent Ra-225. While co-production of hundreds of other isotopes complicated Ac-225 purification, it also provided an opportunity to extract other radionuclides of interest, including a Th-228 (~1 mCi, 1.9 y) generator of Pb-212.
Irradiated thorium was dissolved in a combination of nitric and hydrofluoric acids. Most thorium was removed by precipitation as thorium peroxide, which was easily filtered with minimal Ac or Ra losses. The filtered precipitate was redissolved in strong nitric acid and used as a Th-228/Ra-224/Pb-212 generator. For the filtrate, ion exchange and extraction chromatography resins were used to separate Ac and Ra from remaining Th trace quantities and other spallation products. This approach provided two Ac-225 products with different impurity profiles: directly-produced Ac-225 containing long-lived Ac-227; and Ac-225 produced from decay of Ra-225 fraction, with significantly reduced Ac-227 impurities.
Detailed results from these efforts as well as plans for production scale-up will be presented.