Quantification of trace ²²⁷Ac and other radionuclidic impurities in mass-separated ²²⁵Ac samples produced at...

²²⁵Ac 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 ²²⁵Ac from hundreds of co-produced spallation and fission products. The main radioactive contaminant of concern is ²²⁷Ac  (T_1/2 = 21.8 years), that could preclude extensive medical use if not significantly suppressed. In this work, ²²⁵Ac samples were produced by mass separation of radioactive ion beams extracted from proton-irradiated thorium-based targets. The activity of ²²⁵Ac and other possible contaminants of the samples were measured using complementary gamma- and alpha-decay spectrometry methods, while ²²⁷Ac activity was calculated by performing alpha-decay spectrometry of recoiled progeny from the sample. Using this novel method, accurate measurement of trace ²²⁷Ac activity in ²²⁵Ac 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 ²²⁷Ac to ²²⁵Ac in two samples from irradiated targets were determined to be [Formula: see text] and [Formula: see text] respectively, three orders of magnitude below the ²²⁷Ac activity in ²²⁵Ac products obtained through radiochemical separation. The high separation factor of ²²⁵Ac over ²²⁷Ac suggests the suitability of mass-separated accelerator-based ²²⁵Ac for medical use.