The Effect of Ionising Radiation on the Luminescence Properties of Fluoroperovskites

<p>The luminescence of crystalline compounds can be used to monitor many physical phenomena, including doses of ionising radiation. Optically stimulated luminescence (OSL), thermoluminescence (TL), and radiophotoluminescence (RPL) have been successfully employed in dosimetry. However, few materials possess both the structural and luminescence properties required for medical dosimetry. This thesis aimed to investigate the luminescence features of the class of compounds known as fluoroperovskites. Emphasis was placed on studying the effects of irradiation on the luminescence properties, such that the compounds could be evaluated regarding potential applications in clinical dosimetry. Samples were primarily characterised using photoluminescence (PL), radioluminescence (RL), OSL, RPL, TL, and transmittance spectroscopy. OSL was observed in the majority of samples due to the existence of electron trapping F-type centres. F-centre/Mn complexes were observed in all AMgF3:Mn compounds after irradiation and the energy levels of the complexes in each compound were experimentally determined. The most promising potential dosimeter host material was the near tissue-equivalent NaMgF3. When doped with Mn2+, the compound exhibited RPL via the formation of F-centre/Mn complexes and OSL via several trapping centres. The RPL could be probed independently to the OSL such that the compound could function as a hybrid OSL/RPL dosimeter. In the NaMgF3:Ln compounds, RPL occurred via the radiation-induced reduction Ln3+ → Ln2+ for Ln = Sm, Dy, and Yb. The reduction Sm3+ → Sm2+ was highly stable and could be non-destructively probed independently to the OSL. The Sm doped compound also exhibited radiation-induced conductivity that could be coupled with the RL, such that the compound could function as a real-time hybrid optical/electrical dosimeter. Charge kinetics, thermal quenching, and binding energy models were developed and applied to the compounds. Finally, a two-dimensional readout system was designed and constructed. The capabilities of the system were evaluated using the OSL of NaMgF3:Eu and NaMgF3:Mn. Sensitivities to doses from < 10 mGy to > 1 Gy were obtained along with sub-millimetre spatial resolutions.</p>

The Effect of Ionising Radiation on the Luminescence Properties of Fluoroperovskites

<p>The luminescence of crystalline compounds can be used to monitor many physical phenomena, including doses of ionising radiation. Optically stimulated luminescence (OSL), thermoluminescence (TL), and radiophotoluminescence (RPL) have been successfully employed in dosimetry. However, few materials possess both the structural and luminescence properties required for medical dosimetry. This thesis aimed to investigate the luminescence features of the class of compounds known as fluoroperovskites. Emphasis was placed on studying the effects of irradiation on the luminescence properties, such that the compounds could be evaluated regarding potential applications in clinical dosimetry. Samples were primarily characterised using photoluminescence (PL), radioluminescence (RL), OSL, RPL, TL, and transmittance spectroscopy. OSL was observed in the majority of samples due to the existence of electron trapping F-type centres. F-centre/Mn complexes were observed in all AMgF3:Mn compounds after irradiation and the energy levels of the complexes in each compound were experimentally determined. The most promising potential dosimeter host material was the near tissue-equivalent NaMgF3. When doped with Mn2+, the compound exhibited RPL via the formation of F-centre/Mn complexes and OSL via several trapping centres. The RPL could be probed independently to the OSL such that the compound could function as a hybrid OSL/RPL dosimeter. In the NaMgF3:Ln compounds, RPL occurred via the radiation-induced reduction Ln3+ → Ln2+ for Ln = Sm, Dy, and Yb. The reduction Sm3+ → Sm2+ was highly stable and could be non-destructively probed independently to the OSL. The Sm doped compound also exhibited radiation-induced conductivity that could be coupled with the RL, such that the compound could function as a real-time hybrid optical/electrical dosimeter. Charge kinetics, thermal quenching, and binding energy models were developed and applied to the compounds. Finally, a two-dimensional readout system was designed and constructed. The capabilities of the system were evaluated using the OSL of NaMgF3:Eu and NaMgF3:Mn. Sensitivities to doses from < 10 mGy to > 1 Gy were obtained along with sub-millimetre spatial resolutions.</p>

Development and Characterization of Silver Containing Free Standing Polymer FILMS for Dosimetry Applications

Polymer gels and films, due to their near equivalence to biological tissue, are amongst the most promising future dosimetry tools for medical applications. The application of polymer dose gels is limited by the sensitivity of dose readout methods and dose gel properties. It is a challenge to find suitable dosimeters for registration of doses delivered to the target by orthovoltage therapy units. The application of metal-particle-enriched polymer composites for dose registration in X-ray therapy might be an elegant solution, especially if recent dose-reading technologies exploring advantages of different physical phenomena are involved. In this work, X-rays from the orthovoltage therapy range were used for the irradiation of experimental samples. In addition, radiation-induced processes of formation of silver nanoparticles in AgNO3–PVA gels and in free standing AgNO3PVA films, also containing some additional solvents, namely glycerol, ethanol, and isopropanol, have been investigated, with the aim to apply the developed composites for medical dosimetry purposes. A simple and environmentally friendly method for the formation of free-standing AgPVA films at room temperature was proposed and realized for preparing AgPVA films for investigation. Radiation-induced synthesis of silver nanoparticles in AgPVA composites was investigated, analyzing LPSR-based UV-VIS spectral changes to the irradiated films with respect to irradiation doses, and dose-related tendencies were also evaluated. It was shown that AgPVA films were more sensitive for detection of doses from the interval 0–1.0 Gy, thus indicating potential application of AgPVA films for dosimetry purposes.