Modeling the yields of 225 Ra/ 225 Ac and the resulting 225 Ac radioisotopic purity from proton irradiation of 232 Th at 100–800 MeV

Abstract Objective. High-energy proton irradiation of 232 Th produces both 225 Ac and its precursor 225 Ra, the latter being underexplored despite its potential applicability at relevant facilities. This study aims to provide a theoretical basis for 232 Th-based 225 Ra production by modeling the associated yields and radioisotopic impurity levels. Approach. Production yields of 225 Ra and levels of 228 Ra impurity were calculated using Monte Carlo simulations for proton energies of 100–800 MeV, total 232 Th target thicknesses of 0.125–8 mm, and an irradiation time of 15 d. A theoretical model was developed for predicting the cumulative yield of 225 Ac eluates from a 225 Ra yield. The levels of 228 Ra-derived 228 Ac impurity in 225 Ac eluates and the postelution decay times required to suppress 228 Ac to acceptable thresholds were modeled and computed. Main results. The calculated 225 Ra yields at the end of bombardment for a 15 d irradiation ranged from 2.3 ± 0.3 MBq µA −1 at 100 MeV to 563.1 ± 12.3 MBq µA −1 at 700 MeV. Increases in 225 Ra yield were most pronounced when the proton energy was raised from 100 to 200 MeV, with diminishing returns at higher energies. The cumulative yield of 225 Ac eluates was about 29.1% of a 225 Ra yield under combined conditions of hypothetical and empirical settings. Postelution times of at least 25.1–30.1 h should be allowed to reduce 228 Ac impurity levels to below 0.1%. Significance. The developed models provide a quantitative basis for evaluating and optimizing 225 Ra production via proton irradiation of 232 Th. This study quantitatively predicted the presence of 228 Ac in 225 Ac eluates under various conditions and showed how 228 Ac can be suppressed by introducing minimal postelution decay times.