Supervisors: Senior Research Fellow, Dr. Mihhail Danilkin, Research Fellow, Dr. Mihkel Kerikmäe
Opponents: Academician, Professor Enn Mellikov; Senior Research Fellow, Dr. Irina A. Kamenskikh
Radiation dosimetry measures the absorbed energy in tissue, exposed to ionizing radiation. When dosimetry is based on luminescent detectors, the absorbed energy release is stimulated either thermally or optically to produce the luminescence. Integral intensity of luminescence is proportional to the absorbed dose. Simplicity and convenience of everyday use make the luminescent detectors a valuable means of personnel dose monitoring in medicine and industry. Optically stimulated readout makes the luminescent radiation detectors still more convenient in use. However, there is no ideal detector yet, and all the requirements together are hardly satisfiable in a single material. Designing the better materials and extending their applications requires a deeper understanding of the processes in the radiation detector, especially in connection with the chemical and electronic structure of the materials the detectors are composed of.
The present Thesis studies the energy storage and transfer mechanisms in three different materials. CaF2:Mn has a wide range of the measurable radiation doses. SrSO4:Eu is one of the most sensitive materials known. Li2B4O7-based detectors have the best tissue-equivalence (their effective atomic number is very close to that of a human tissue). The formation of effective structure of trapping levels for energy storage is connected with redox transformations of doped impurities at the moment of high-temperature treatment of the detectors. However, the energy transfer conditions and mechanisms are very different in the studied materials. Both experimental and comparative investigations are undertaken. Luminescence, thermoluminescence, kinetics, optical stimulation and radiation-induced absorption spectra measurements, and EPR studies in connection with the variations of preparation procedures compose the experimental part of the present work. The results are compared and critically analysed together with the previously published by other investigators materials. Models of traps and energy storage mechanisms are proposed. The results of the Thesis will be useful for designing new effective radiation detectors.