Quantification of trace Ac and other radionuclidic impurities in mass-separated Ac samples produced at CERN-MEDICIS.

Ac is a promising candidate medical radionuclide for targeted alpha therapy of advanced stage cancers. One of the main production pathways is the high-energy proton spallation of thorium-based targets, that requires an efficient, nuclide-selective separation method to recover Ac from hundreds of co-produced spallation and fission products. The main radioactive contaminant of concern is Ac  (T = 21.8 years), that could preclude extensive medical use if not significantly suppressed. In this work, Ac samples were produced by mass separation of radioactive ion beams extracted from proton-irradiated thorium-based targets. The activity of Ac and other possible contaminants of the samples were measured using complementary gamma- and alpha-decay spectrometry methods, while Ac activity was calculated by performing alpha-decay spectrometry of recoiled progeny from the sample. Using this novel method, accurate measurement of trace Ac activity in Ac samples was performed much faster than with conventional spectrometry techniques, thanks to its 10,000-fold increase in relative sensitivity. The end of collection activity ratio of Ac to Ac in two samples from irradiated targets were determined to be [Formula: see text] and [Formula: see text] respectively, three orders of magnitude below the Ac activity in Ac products obtained through radiochemical separation. The high separation factor of Ac over Ac suggests the suitability of mass-separated accelerator-based Ac for medical use.