Desenvolveu-se um sistema termoluminescente especial, para operar a partir da temperatura do nitrogênio líquido, que permite, ainda, a obtenção do espectro de emissão termoluminescente da amostra. Com o uso deste sistema, estudou-se a termoluminescência do LiF:Mg,Ti (TLD-100), irradiado a 77 K, desde a temperatura de irradiação até 315K. Neste intervalo de temperaturas foram determinados sete picos de emissão termoluminescente em 139, 153, 194, 240, 260, 283 e 300K. Através de experiências de variação do tratamento térmico da amostra, linearidade, fototransferência e destruição óptica, o pico de emissão termoluminescente em 139K foi associado a centros de buracos Vk, enquanto que os demais a armadilhas de elétrons. Os sete picos de emissão termoluminescente emitem em três comprimentos de onda, 270, 300 e 420nm, sendo que a banda de emissão em 270nm é a mais intensa no caso dos picos de emissão termoluminescente em 139 e 153K, sobressaindo-se as bandas de emissão em 300 e 420nm para os demais picos de emissão termoluminescente. A banda de emissão em 270nm foi associada a centros de recombinação para buracos liberados dos centros Vk, centros estes diferentes daqueles, normalmente, associados à banda de emissão em 420nm. Quanto à banda de emissão em 300nm, esta foi associada à interação entre elétrons e centros Vk. Verificou-se que os picos de emissão termoluminescente em 139, 153, 194 e 260K obedecem à cinética de primeira ordem. As energias de ativação determinadas para estes picos foram, respectivamente, 0,26, 0,29, 0,49 e 0,82eV. / A special thermoluminescent system was deve1oped. It is able to operate right from liquid nitrogen temperature and also permits the determination of the sample thermoluminescent emission spectrum. Using this system, the thermoluminescence displayed by 77K irradiated LiF:Mg,Ti (TLD-100), from the irradiation temperature to 315 K, was studied. In this temperature range seven glow peaks, at 139, 153, 194, 240, 260, 283 and 300 K, were determined. Based upon different annealing procedures, linearity, phototransference and optical bleaching experiments, the glow peak at 139 K was related to Vk hole centres, while the remaining glow peaks were associated to electron traps. The seven glow peaks emit at three wavelengths, namely, 270, 300 and 420 nm. The emission band at 270 nm is the most intense in the case of glow peaks at 139 and 153 K. For the remaining glow peaks, the emission bands at 300 and 420 nm are the most important ones. The emission band at 270 nm was related to the recombination of Vk holes at recombination centres other than those ones, normally, associated to the emission band at 420 nm. The emission band at 300 nm was related to the recombination of electrons and Vk centres. It was verified that the glow peaks at 139, 153, 194 and 260 K obey the first order kinetics. For these glow peaks, the determined activation energies were, respectively, 0,26, 0,29, 0,49 and 0,82 eV.

Thesis (M. Sc.)--University of Adelaide, Dept. of Physics, 1987. / Includes bibliographical references (leaves 131-139).

Thesis (Ph. D.)--University of Washington, 1997. / Vita. Includes bibliographical references (leaves [131]-140).

Thesis (M.S.)--Oregon State University, 2010. / Printout. Includes bibliographical references (leaves 86-87). Also available on the World Wide Web.

Carbon-doped aluminium oxide, α-Al₂O₃ : C, is a highly sensitive luminescence dosimeter. The high sensitivity of α-Al₂O₃ : C has been attributed to large concentrations of oxygen vacancies, F and F⁺ centres, induced in the material during its preparation. The material is prepared in a highly reducing atmosphere in the presence of carbon. In the luminescence process, electrons are trapped in F-centre defects as a result of irradiation of the material. Thermal or optical release of trapped electrons leads to emission of light, thermoluminescence (TL) or optically stimulated light (OSL) respectively. The thermoluminescence technique is used to study point defects involved in luminescence of α-Al₂O₃ : C. A glow curve of α-Al₂O₃ : C, generally, shows three peaks; the main dosimetric peak of high intensity (peak II) and two other peaks of lower intensity called secondary glow peaks (peaks I and III). The overall aim of our work was to study the TL mechanisms responsible for secondary glow peaks in α-Al₂O₃ : C. The dynamics of charge movement between centres during the TL process was studied. The phototransferred thermoluminescence (PTTL) from secondary glow peaks was also studied. The kinetic analysis of TL from secondary peaks has shown that the activation energy of peak I is 0.7 eV and that of peak III, 1.2 eV. The frequency factor, the frequency at which an electron attempts to escape a trap, was found near the range of the Debye vibration frequency. Values of the activation energy are consistent within a variety of methods used. The two peaks follow first order kinetics as confirmed by the TM-Tstop method. A linear dependence of TL from peak I on dose is observed at various doses from 0.5 to 2.5 Gy. The peak position for peak I was also independent on dose, further confirmation that peak I is of first order kinetics. Peak I suffers from thermal fading with storage with a half-life of about 120 s. The dependence of TL intensity for peak I increased as a function of heating rate from 0.2 to 6ºCs⁻¹. In contrast to the TL intensity for peak I, the intensity of TL for peak III decreases with an increase of heating rate from 0.2 to 6ºCs⁻¹. This is evidence of thermal quenching for peak III. Parameters W = 1.48 ± 0:10 eV and C = 4 x 10¹³ of thermal quenching were calculated from peak III intensities at different heating rates. Thermal cleaning of peak III and the glow curve deconvolution methods confirmed that the main peak is actually overlapped by a small peak (labeled peak IIA). The kinetic analysis of peak IIA showed that it is of first order kinetics and that its activation energy is 1:0 eV. In addition, the peak IIA is affected by thermal quenching. Another secondary peak appears at 422ºC (peak IV). However, the kinetic analysis of TL from peak IV was not studied because its intensity is not well defined. A heating rate of 0.4ºCs⁻¹ was used after a dose of 3 Gy in kinetic analysis of peaks IIA and III. The study of the PTTL showed that peaks I and II were regenerated under PTTL but peak III was not. Various effects of the PTTL for peaks I and II for different preheating temperatures in different samples were observed. The effect of annealing at 900ºC for 15 minutes between measurements following each illumination time was studied. The effect of dose on secondary peaks was also studied in this work. The kinetic analysis of the PTTL intensity for peak I showed that its activation energy is 0.7 eV, consistent with the activation energy of the normal TL for peak I. The PTTL intensity from peak I fades rapidly with storage compared with the thermal fading from peak I of the normal TL. The PTTL intensity for peak I decreases as a function of heating rate. This decrease was attributed to thermal quenching. Thermal quenching was not observed in the case of the normal TL intensity. The cause of this contrast requires further study.

published_or_final_version / Earth Sciences / Doctoral / Doctor of Philosophy

This study investigated the photo-excitation and thermoluminescence properties of diamonds which were synthesised primarily for thermoluminescence dosimetry. For investigations of thermally stimulated processes occurring in these crystals an analysis of the thermoluminiscence & low spectra and the temperature dependent isothermal decay spectra was undertaken [Abbreviated abstract. Open document to view full version] / GR2016

Thesis (Ph. D.)--University of Hong Kong, 2008. / Includes bibliographical references (leaf 135-150) Also available in print.

Typescript (photocopy). / Digitized by Kansas Correctional Industries

published_or_final_version / Radioisotope / Doctoral / Doctor of Philosophy