Synthesis, Stability and Characterization of Indirect Conversion Materials for the Measurement of Dose at a Synchrotron Biomedical Imaging and Therapy Beamline

Novel dosimetric materials to ensure properly calibrated x-ray beam profiles are required to facilitate the implementation of Microbeam Radiation Therapy in cancer treatment. Indirect conversion dosimetric materials are explored for possible future applications in Microbeam Radiation Therapy devices. The indirect conversion materials barium borophosphates, barium fluorophosphates with sodium ion modifier, and barium aluminosilicates were synthesized and studied. Each synthesized compound was also doped (or additionally co-doped) with a rare-earth compound. The rare-earth compounds used for doping included samarium (III) oxide, and samarium (III) fluoride. Codoping was explored with the compound erbium (III) chloride. Synthesized samples were x-ray irradiated at the Biomedical Imaging and Therapy beamline of the Canadian Light Source and also at the University of Saskatchewan. Experimental characterization methods of dosimetric material samples included x-ray luminescence, photoluminescence, electron spin resonance, Raman spectroscopy, absorbance spectroscopy, x-ray diffraction, differential scanning calorimetry, and modulated differential scanning calorimetry. The materials are experimentally characterized and determined for their merit in further research and development. All materials were found to scintillate, and some were found to function as x-ray storage phosphors as well. The barium borophosphates and also the barium fluorophosphates with sodium ion modifier possessed x-ray storage functionality according to photoluminescence spectra. An absorbance peak was observed after x-ray irradiation for barium fluorophosphates. Electron spin resonance data suggest that x-ray irradiation forms two similar types of paramagnetic defects for barium borophosphates. It appears that these defects are oxygen hole centres, which form during the indirect conversion process of samarium dopant cations. Indirect conversion involves samarium cation valency change from the 3+ to 2+ oxidation state, occurring when an electron is captured by the cation. Thermal analysis of the barium fluorophosphates by differential scanning calorimetry and modulated scanning calorimetry indicate preferential properties and moderate glass forming ability for manufacturing processes. It is concluded that barium fluorophosphates are best suited for dosimetric detectors, and secondly, barium borophosphates. Finally, future studies on materials for dosimetry in Microbeam Radiation Therapy are recommended