%0 Thesis
%T Isotope separation of Ac-225 and Ra-225 for medical purposes
%U https://zenodo.org/records/18086727
%X At the time of writing, global efforts are underway to produce the medical radionuclide Ac-225 from high-energy accelerator-based methods to support the growing demand for targeted alpha therapy drugs. Almost all known approaches rely on radiochemical separation of Ac-225 and its beta-decay parent Ra-225 from metallic Th-232 targets irradiated with protons. Although the method is efficient, the Ac-225 produced by this method contains the isotopic contaminant Ac-227 that could preclude safe handling in clinical environments. Furthermore, radiochemical extraction of Ac-225 necessarily requires the dissolution of the Th target and produces high levels of liquid radioactive waste. In this thesis, studies on the extraction of Ac-225 and its beta-decay parent Ra-225 as mass-separated ion beams from proton-irradiated thick ThCx targets are presented. This technique allows the nuclear targets to be used multiple times, and importantly is the only current potential purification method with isotope selectivity. As a results of these studies, clinically-relevant quantities of pure Ac-225 have been produced at CERN-MEDICIS from 100 g ThCx targets irradiated with 1.4 GeV protons for the order of 1 d. Several experiments were performed to understand the conditions necessary for the beam production, and to characterize the produced samples. Firstly, the Ac-225 ionization efficiency with surface ionization and a dual resonance laser ionization scheme was determined to be an encouraging 15%. During these tests, the temperature regime required for Ac to reach a vapor pressure sufficient to form ion beams at picoamp currents when heated from its nitrate salt were determined. The experiment was repeated for Ac-225 heated and dried on a mimic ThO2 matrix, that enabled the understanding that chemical interactions between Ac-225 and the ThO2 target material meant that higher, but still attainable target temperatures were required for efficient Ac-225 extraction. Extensive nuclear decay spectrometry campaigns were then performed on several mass-separated Ac-225 samples produced from both mimic target material spiked with Ac-225 and Ac-227 radiotracers, as well as development- and production-scale irradiated Th-based targets. A spectrometry technique was developed specifically for the detection of trace Ac-227 activity that could not be measured by standard nuclear-decay spectrometry techniques. Using this technique, the Ac-227-content of Ac-225 samples was quantified. Finally, through analysis of four production-scale ThCx irradiations, extraction efficiencies and extraction rates of both Ac-225 and Ra-225 ion beams have been determined. The optimum range of target temperatures and ion source temperatures required for efficient collection of ion beams of these radionuclides have been quantified through these studies. The interpretation of the results has led to the conclusion that most Ac-225 is produced due to decay filiation by R-225a, while the extraction efficiency of Ac-225 is release limited. The thesis discusses these results in the context of the contribution of Ac-225 and Ra-225 produced by mass-separation techniques to the potential future Ac-225 supply for medical applications.
%G eng
%A Johnson, Jake
%D 2024-11-18
%K ion sources
radioactive ion beams
thesis