Thermoluminescence and phototransferred thermoluminescence of tanzanite
- Authors: Opoku, Kingsley Acheampong
- Date: 2024-10-11
- Subjects: Thermoluminescence , Thermoluminescence dosimetry , Tanzanite Thermal properties , Dose–response relationship , Thermal fade , Ionizing radiation
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/464914 , vital:76556
- Description: The thermoluminescence (TL) and phototransferred thermoluminescence (PTTL) properties of tanzanite, an extremely rare gem mineral, have been investigated. While tanzanite shows sensitivity to thermal and optical stimulation of luminescence techniques used for defect probing in insulators, it has received little attention in this regard. A glow curve corresponding to 70 Gy and measured at 1 °C s-1 revealed a high intensity peak at 74 °C (peak I) and two secondary peaks at 138 and 186 °C (peaks II and III). All the peaks exhibit a first order kinetics characteristics, as their positions remained unaffected by changes in either dose or partial heating (𝑇𝑚 − 𝑇𝑠𝑡𝑜𝑝). For variable doses from 10 to 200 Gy, the dose response of each peak is sublinear from the analysis of supralinearity indices. Peak I fades at room temperature when readout is delayed following irradiation, and this loss is due to thermal fading. The secondary peaks do not fade. Various methods of kinetic analysis were used to compute the kinetic parameters. For the respective peaks, the activation energy is about 0.84, 1.00 and 1.19 eV. All the peaks suffer thermal quenching with increasing heating rate. Continuous wave optically stimulated luminescence measurements were conducted to supplement the TL analysis with the aim of evaluating the kinetic parameters activation energy of thermal assistance (𝐸𝑎) and quenching (𝛥𝐸). The OSL source traps are the same as the TL source traps and occur within 40 to 90 °C, 110 to 145 °C and 160 to 220 °C. The kinetic parameter 𝛥𝐸 when luminescence from all the source traps is considered is comparable to that when source traps within 110 to 220 °C are measured and does not depend on the dose (10, 50 or 70Gy). Except for irradiation to 10 Gy, 𝐸𝑎 is also comparable. For traps within 160 to 220 °C, 𝛥𝐸 is comparable for the different doses but higher than that of the other traps, and a similar pattern was observed for 𝐸𝑎. Measurement of the PTTL signal induced by 470 nm blue LEDs following irradiation to 150 Gy and preheating to 158 °C showed that the TL peaks I and II were reproduced under phototransfer. The analysis for order of kinetics and dose response yielded the same results as the convention TL peaks. The model used to describe the PTTL intensity time response profiles shows that the PTTL emanates from a system of one acceptor and three donors, where the latter is a conglomerate of an unknown number of peaks. , Thesis (MSc) -- Faculty of Science, Physics and Electronics, 2024
- Full Text:
- Date Issued: 2024-10-11
- Authors: Opoku, Kingsley Acheampong
- Date: 2024-10-11
- Subjects: Thermoluminescence , Thermoluminescence dosimetry , Tanzanite Thermal properties , Dose–response relationship , Thermal fade , Ionizing radiation
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/464914 , vital:76556
- Description: The thermoluminescence (TL) and phototransferred thermoluminescence (PTTL) properties of tanzanite, an extremely rare gem mineral, have been investigated. While tanzanite shows sensitivity to thermal and optical stimulation of luminescence techniques used for defect probing in insulators, it has received little attention in this regard. A glow curve corresponding to 70 Gy and measured at 1 °C s-1 revealed a high intensity peak at 74 °C (peak I) and two secondary peaks at 138 and 186 °C (peaks II and III). All the peaks exhibit a first order kinetics characteristics, as their positions remained unaffected by changes in either dose or partial heating (𝑇𝑚 − 𝑇𝑠𝑡𝑜𝑝). For variable doses from 10 to 200 Gy, the dose response of each peak is sublinear from the analysis of supralinearity indices. Peak I fades at room temperature when readout is delayed following irradiation, and this loss is due to thermal fading. The secondary peaks do not fade. Various methods of kinetic analysis were used to compute the kinetic parameters. For the respective peaks, the activation energy is about 0.84, 1.00 and 1.19 eV. All the peaks suffer thermal quenching with increasing heating rate. Continuous wave optically stimulated luminescence measurements were conducted to supplement the TL analysis with the aim of evaluating the kinetic parameters activation energy of thermal assistance (𝐸𝑎) and quenching (𝛥𝐸). The OSL source traps are the same as the TL source traps and occur within 40 to 90 °C, 110 to 145 °C and 160 to 220 °C. The kinetic parameter 𝛥𝐸 when luminescence from all the source traps is considered is comparable to that when source traps within 110 to 220 °C are measured and does not depend on the dose (10, 50 or 70Gy). Except for irradiation to 10 Gy, 𝐸𝑎 is also comparable. For traps within 160 to 220 °C, 𝛥𝐸 is comparable for the different doses but higher than that of the other traps, and a similar pattern was observed for 𝐸𝑎. Measurement of the PTTL signal induced by 470 nm blue LEDs following irradiation to 150 Gy and preheating to 158 °C showed that the TL peaks I and II were reproduced under phototransfer. The analysis for order of kinetics and dose response yielded the same results as the convention TL peaks. The model used to describe the PTTL intensity time response profiles shows that the PTTL emanates from a system of one acceptor and three donors, where the latter is a conglomerate of an unknown number of peaks. , Thesis (MSc) -- Faculty of Science, Physics and Electronics, 2024
- Full Text:
- Date Issued: 2024-10-11
Thermoluminescence of natural quartz
- Authors: Lontsi Sob, Aaron Joel
- Date: 2014
- Subjects: Thermoluminescence , Quartz , Thermoluminescence dosimetry
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5543 , http://hdl.handle.net/10962/d1013358
- Description: The kinetic and dosimetric features of the main thermoluminescence peak of quartz have been investigated in unannealed as well in quartz annealed at 500˚C for 10 minutes. The main peak is found at 92 and 86˚C respectively for aliquots of unannealed and annealed samples irradiated to 10 Gy and heated at 5.0˚C/s. For each sample, the intensity of the main peak is enhanced with repetitive measurement whereas its maximum temperature is unaffected. The peak position of the main peak in each sample is independent of the irradiation dose and this, together with its fading characteristics are consistent with first-order kinetics. For low doses, typically between 2 and 10 Gy, the dose response of the main peak in each sample is linear. In the intermediate dose range from 10 to 60 Gy, the growth of the main peak in each sample is sub-linear and for greater doses, in the range from 60 Gy to 151 Gy, it is linear again. The half-life of the main peak of the unannealed sample is about 1.3 h whereas that of the annealed sample is about 1.2 h. The main peak in each sample can be approximated to a first-order glow peak. As the heating rate increases, the intensity of the main peak in each sample decreases. This is evidence of thermal quenching. The main peak in each sample is the only peak regenerated by phototransfer. The resulting phototransferred peak occurs at the same temperature as the original peak and has similar kinetic and dosimetric features. For a preheat temperature of 120˚C, the intensity of the phototransferred peak in each sample increases with illumination time up to a maximum and decreases afterwards. At longer illumination times (such as 30 min up to 1 h), no further decrease in the intensity of the phototransferred peak is observed. The traps associated with the 325˚C peak are the main source of the electrons responsible for the regenerated peak. Radioluminescence emission spectra were also measured for quartz annealed at various temperatures. Emission bands in quartz are affected by annealing and irradiation. A strong enhancement of the 3.4 eV (~366 nm) emission band is observed in quartz annealed at 500˚C. A new emission band which grows with annealing up to 1000˚C is observed at 3.7 eV (~330 nm) for quartz annealed at 600˚C. An attempt has been made to correlate the changes in radioluminescence emission spectra due to annealing with the influence of annealing on luminescence lifetimes in quartz.
- Full Text:
- Date Issued: 2014
- Authors: Lontsi Sob, Aaron Joel
- Date: 2014
- Subjects: Thermoluminescence , Quartz , Thermoluminescence dosimetry
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5543 , http://hdl.handle.net/10962/d1013358
- Description: The kinetic and dosimetric features of the main thermoluminescence peak of quartz have been investigated in unannealed as well in quartz annealed at 500˚C for 10 minutes. The main peak is found at 92 and 86˚C respectively for aliquots of unannealed and annealed samples irradiated to 10 Gy and heated at 5.0˚C/s. For each sample, the intensity of the main peak is enhanced with repetitive measurement whereas its maximum temperature is unaffected. The peak position of the main peak in each sample is independent of the irradiation dose and this, together with its fading characteristics are consistent with first-order kinetics. For low doses, typically between 2 and 10 Gy, the dose response of the main peak in each sample is linear. In the intermediate dose range from 10 to 60 Gy, the growth of the main peak in each sample is sub-linear and for greater doses, in the range from 60 Gy to 151 Gy, it is linear again. The half-life of the main peak of the unannealed sample is about 1.3 h whereas that of the annealed sample is about 1.2 h. The main peak in each sample can be approximated to a first-order glow peak. As the heating rate increases, the intensity of the main peak in each sample decreases. This is evidence of thermal quenching. The main peak in each sample is the only peak regenerated by phototransfer. The resulting phototransferred peak occurs at the same temperature as the original peak and has similar kinetic and dosimetric features. For a preheat temperature of 120˚C, the intensity of the phototransferred peak in each sample increases with illumination time up to a maximum and decreases afterwards. At longer illumination times (such as 30 min up to 1 h), no further decrease in the intensity of the phototransferred peak is observed. The traps associated with the 325˚C peak are the main source of the electrons responsible for the regenerated peak. Radioluminescence emission spectra were also measured for quartz annealed at various temperatures. Emission bands in quartz are affected by annealing and irradiation. A strong enhancement of the 3.4 eV (~366 nm) emission band is observed in quartz annealed at 500˚C. A new emission band which grows with annealing up to 1000˚C is observed at 3.7 eV (~330 nm) for quartz annealed at 600˚C. An attempt has been made to correlate the changes in radioluminescence emission spectra due to annealing with the influence of annealing on luminescence lifetimes in quartz.
- Full Text:
- Date Issued: 2014
Thermoluminescence of secondary glow peaks in carbon-doped aluminium oxide
- Authors: Seneza, Cleophace
- Date: 2014
- Subjects: Thermoluminescence , Aluminum oxide , Thermoluminescence dosimetry
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5537 , http://hdl.handle.net/10962/d1013053
- Description: 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.
- Full Text:
- Date Issued: 2014
- Authors: Seneza, Cleophace
- Date: 2014
- Subjects: Thermoluminescence , Aluminum oxide , Thermoluminescence dosimetry
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5537 , http://hdl.handle.net/10962/d1013053
- Description: 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.
- Full Text:
- Date Issued: 2014
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