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The evolution of the thermoluminescence glow curve of a natural Ca-Be rich aluminosilicate after annealing treatments at different temperatures has been studied in order to evaluate the changes in the trapped charge distribution. The glow curve consists of a single broad peak that continuously shifts toward higher temperatures when the sample is pr...
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... [Ca 4 Be 2 Al 2 Si 9 O 26 (OH) 2 ] is one of the most efficient phosphor with a very high sensitivity to radiation exposure. Bavenite fibrous samples were collected in a large rock cavity hosted in a pegmatite body in the granite massif of Bustarviejo (Madrid, Spain). The crystal was studied under scanning electron microscopy (SEM) performed in a Philips XL20 SEM at accelerating voltages of 20–30 kV. Samples were coated with gold (20 nm) in a Bio- Rad SC515 sputter coating unit. Energy-dispersive X-ray microanalyses were obtained using a Phillips EDAX PV9900 with a light element detector type ECON. Bavenite appears as cotton-like white masses covering these hydrothermal minerals. Crystals show fragile prismatic-needle habits with a random 3-D orientation produced during the process of granite cutting and sample collection. ( Figure 1). The TL glow curves were obtained using an auto- mated Risø TL system model TL DA-12 (6) , this reader is provided with an EMI 9635 QA photomul- tiplier and the emission was observed through a blue filter (a FIB002 of the Melles-Griot Company) where the wavelength is peaked at 320–480 nm; FWHM is 80 Æ 16 nm and peak transmittance (minimum) is 60%. All the TL measurements were performed using a linear heating rate of 5 C s À 1 from room temperature up to 550 C in a N 2 atmosphere. Four aliquots of 5.0 Æ 0.1 mg each of Bavenite were used for each measurement. The sample was carefully powdered with an agate pestle and mortar to avoid triboluminescence (7) . The incandescent background was subtracted from the TL data. The TL glow curves have been analysed using a fitting program based on an iterative Levenberg– Marquard algorithm to minimise the corresponding w 2 function (8) . For first-order kinetics and a linear heating profile T ( t ) 1⁄4 T 0 þ b t , the intensity of the glow peak owing to a continuous distribution of trapping centres n ( t ) is given by (4,9) ...
Citations
... where I and I m are TL intensities for a given temperature (T, in K) or at peak maximum (Tm) and temperature linearly increases with time (t) from T 0 to T, T(t) = T 0 + βt, β ( • C/s) is the linear heating rate; E (eV) is the trap activation energy; k (eV·K −1 ) is the Boltzmann constant; and b is the kinetic order parameter. In case of continuous energy distribution of traps present in material, usually exponential or gaussian functions are used, which can be described by Equations (7) and (8) [49][50][51]: ...
The phosphate glass samples doped with Tb2O3 oxide (general formula: P2O5-Al2O3-Na2O-Tb2O3) were synthesized and studied for usage in high-dose radiation dosimetry (for example, in high-activity nuclear waste disposals). The influence of terbium concentration on thermoluminescent (TL) signals was analyzed. TL properties of glasses were investigated using various experimental techniques such as direct measurements of TL response vs. radiation dose, Tmax–Tstop and VHR (various heating rate) methods, and glow curve deconvolution analysis. The thermoluminescence dosimetry (TLD) technique was used as the main investigation tool to study detectors’ dose responses. It has been proved that increasing the concentration of terbium oxide in glass matrices significantly increases the thermoluminescence yield of examined material. For the highest dose range (up to 35 kGy), the dependence of the integrated thermoluminescent signals vs. dose can be considered as a saturation-type curve. Additional preheating of samples improves linearity of signal vs. dose dependencies and leads to a decrease of the signal loss over time. All obtained data suggest that investigated material can be used in high-dose radiation dosimetry. Additional advantages of the investigated dosimetric system are its potential ability to re-use the same dosimeters multiple times and the fact that reading dosimeters only requires usage of a basic TL reader without any modifications.
... Where n(E i )dE is the concentration of the trapped electron in the interval dE. For Gaussian, exponential, and uniform distributions, the concentration of the trapped electrons within the interval δE are given, respectively by [20,21]; ...
The theoretical assumptions of the analytical expressions characterizing the thermoluminescence glow-peak arising from a continuous trap-depth distribution have been investigated. The sets of the differential equations governing the electrons' transitions within a continuous trap-depth distribution during the irradiation and heating stages have been numerically solved. The analytical expressions are essentially based on a theoretical assumption that correlates the concentrations of the trapped electrons with the distribution of the trap depths in the bandgap. This correlation could not be considered in the numerical solution, since the irradiation stage is entirely independent of the trap depth. Thus, the final values of the instantaneous trap-filling functions of the irradiation stage do not depend on the trap depth, but rather on the trap capacity and the trapping probability coefficient. Consequently, in the numerical solution, the distribution of the trap depths and the distribution of the trapped electrons are independent. This inconsistency between the numerical solution and the analytical expression has led to differences in the shape of the thermoluminescence glow peaks resulting from the same trap-depth spectrum.
... (Horowitz and Yossian, 1995), has been obtained when an exponential distribution is assumed for peak I and a Gaussian one for peaks III and IV. The presence of an exponential distribution for the lowest temperature peak can be explained as a consequence of the emptying process affecting the shallower levels thus remaining only the deepest exponential tail (Sakurai et al., 2001;Gómez-Ros et al., 2006). ...
... Then, consistent results have been obtained that permitted to identify four components from 50 to 270ºC originated by a complex trap structure: continuous energy distributions for peaks I, III and IV, and GOK discrete trapping level for peak II. The obtained exponential energy distribution for peak I a consequence of the thermal emptying of the shallower levels at room temperature, already found in some materials (Sakurai et al., 2001;Gómez-Ros et al., 2006). ...
This work presents the characterization of the thermoluminescence (TL) glow curve of a copper and silver doped lithium tetraborate (Li2B4O7:Cu,Ag) made using three different methods to identify the number of peaks, the trap structure and the kinetics parameters: TM-Tstop, glow curve fitting (GCF) and various heating rates (VHR).
The obtained results can be consistently explained assuming four TL glow peaks in the region 50 - 270 °C, originated by a complex trap structure: continuous energy distributions for peaks I, III and IV, and general order kinetics (GOK) discrete trapping level for peak II. Quite similar activation energy values have been obtained by GCF and VHR methods.
... Several methods have been developed and applied to obtain the trap parameters of a single TL peak [1,3,5,10,[14][15][16][17][18][19][20][21][22][23], however the number is dwindling in the case of overlapped peaks [24][25][26][27][28][29]. The methods proposed to determine the trap parameters must take into consideration the effects of overlapped peaks. ...
... In sequence, after calculating the value of b, the value of the activation energy E can be estimated using Equation (14) or (15). Hence, using b, E, Tm, and Im, the values of S or S" can be determined using Equations (16) and (17) for the first and general order, respectively. Eventually, the relative value of the initial concentration of the electrons can be estimated according to Equation (18). ...
... The trap parameters estimated for Peak 3, left, and Peak 4, right, calculated using equations(13)(14)(15)(16)(17)(18) with the values of temperatures, intensities, and areas used in the calculations. ...
Thermoluminescence (TL) properties of La2O3: Dy3+, Li+, and La2O3: Eu3+, Li+, exposed to 5.12 Gy of beta radiation, and recorded at different heating rates 0.5, 1, 2, 3, 4, and 5 °C s−1 (from Molefe et al., paper 2019), were analyzed and the trap parameters were determined in this study. These parameters include the order of kinetics b, the activation energy E (eV), the frequency factor S (s−1), or the pre-exponential factor S’’ (s−1), and the initial concentration of trapped electrons no (cm−3). A new non-linear curve fitting technique, based on the general order kinetic equation and the outcomes of Hoogenstraaten’s Method, was established and applied on the TL glow peaks of La2O3: Dy3+, Li+. The fitting technique was evaluated by calculating the R-square and figure of merit (FOM) values. The results revealed that the FOM values are <1%, and the R-square values are >0.997, which demonstrates an excellent convergence between experimental and fitted curves. A modified technique based on the three-points analysis method was exploited to deconvolute complex TL glow curves of La2O3: Eu3+, Li+, and in turn to determine the trap parameters the method disclosed that each TL glow curve consists of four peaks. The trap parameters of the individual peaks were numerically determined. The fading, as a function of storage temperature and time, from the TL signals of the investigated materials was predicted and discussed based on the calculated trap parameters. The results support the value of the materials for employment in radiation dosimeter applications with a low fading fraction.
... Following previous works (Gómez-Ros et al., 2006a), two mathematical forms of the trap distributions have been considered: an exponential and a Gaussian distribution. For the Gaussian distribution, the trap density is: ...
Deconvolution analysis of the thermoluminiscent (TL) glow curves proved to be a good complementary method to characterize the individual glow peaks by fitting their kinetic parameters. In this work, new software has been developed for the automatic deconvolution of TL glow curves, assuming either discrete or continuous distribution of trapping centres. The guess estimation of the kinetic parameters is done automatically and can be manually modified, thus allowing the use of the software for routine, processing a large number of measurements, as well as for research purposes. The equations, the methods and the results of the first test are described in detail. The software has been developed by integrating Fortran code and Visual Studio tools to create a graphic easy-to-use environment and permits to obtain the fitted values for the parameters according to the considered model.
... These glow curves were analyzed considering the continuous distribution of trapping states model, because they exhibited a complex luminescence glow emission. However, there are other possibilities to analyze the trapped charge assuming a Gaussian or exponential distribution (Gomez-Ros et al., 2006a) due to the thermal release of charge carriers from the trapping centers. Because our TL glow curve structure is complex, a computerized deconvolution (CGCD) was used (Kitis and Gomez-Ros, 2000) to obtain the kinetic parameters; effective activation energy E ff [eV], ΔE [eV] and the frequency factor s [s −1 ] of the traps involved in TL process. ...
Single Wall Carbon Nanotubes (SWNT) synthesized by the hydrogen-arc-discharge method were tested as thermoluminescent (TL) material and found to be highly resistant to gamma radiation. Gamma irradiation of the as-prepared material with doses between 1 and 20 kGy induced changes on the morphology of the SWNT, such as nanoloops, as observed by Scanning Electron Microscopy. From X-ray diffraction, the as-prepared material shows content of various forms of carbon, including nanotubes, hexagonal carbon (graphite), and rhombohedral carbon too. The full width at half maximum (FWHM) of diffraction peaks remain practically unchanged after irradiation. The glow curves show a single TL peak centered at about 449 K. Because the complex structure of the glow curves, it seems that the TL signal could be produced by a trap distribution instead of a single level of traps. To dilucidate the mechanism responsible of glow curves and the value of activation energy of traps, kinetic parameters like Eeff, ΔE, and s of experimental the glow curves have been analyzed using computerized glow curve deconvolution (CGCD) considering a continuous distribution of trapping levels, peak shape and initial rise methods, as well as heuristic equations. The measured TL dosimetric properties may be summarized as follows: (a) moderate reproducibility of the TL signal (coefficient of variation 24.87%); (b) main peak activation energy of 1.206 eV; (c) threshold dose of ~1 kGy; (d) TL-sensitivity of ~7.0 × 10⁻⁴; (e) human bone equivalence, i.e., high-Z material, Zeff = 15 and, (f) wide linear range of TL dose-response in the range 0.170–2.5 kGy.
... The distribution of traps with different energy states can be calculated by different methods. According to McKeever's method, 35 the number of traps with energy E in a crystal follows the Boltzmann distribution, 24,32,33,36 ...
The mechanoluminescent (ML) sensor is a newly developed non-invasive technique for stress/strain measurement. However, its application has been mostly restricted to qualitative measurement due to the lack of a well-defined relationship between ML intensity and stress. To achieve accurate stress measurement, an intensity ratio model was proposed in this study to establish a quantitative relationship between the stress condition and its ML intensity in elastic deformation. To verify the proposed model, experiments were carried out on a ML measurement system using resin samples mixed with the sensor material SrAl2O4:Eu2+, Dy3+. The ML intensity ratio was found to be dependent on the applied stress and strain rate, and the relationship acquired from the experimental results agreed well with the proposed model. The current study provided a physical explanation for the relationship between ML intensity and its stress condition. The proposed model was applicable in various SrAl2O4:Eu2+, Dy3+-based ML measurement in elastic deformation, and could provide a useful reference for quantitative stress measurement using theMLsensor in general.
... Quasi-continuous distributions of trap depths may be expected in non-crystalline materials, as a result of the large number of possible surroundings of the defects. Examples have been given for feldspars [17], Ca-Be rich aluminosilicate (Bavenite) [18], and chariote silicate, a gemstone material [19]. They have also been presented for synthetic materials for dosimetry like [29], as well as for scintillators GAGG:Ce and LuAG:Pr [30]. ...
Thermally stimulated luminescence (TSL) is known as a technique used in radiation dosimetry and dating. However, since the luminescence is very sensitive to the defects in a solid, it can also be used in material research. In this review, it is shown how TSL can be used as a research tool to investigate luminescent characteristics and underlying luminescent mechanisms. First, some basic characteristics and a theoretical background of the phenomenon are given. Next, methods and difficulties in extracting trapping parameters are addressed. Then, the instrumentation needed to measure the luminescence, both as a function of temperature and wavelength, is described. Finally, a series of very diverse examples is given to illustrate how TSL has been used in the determination of energy levels of defects, in the research of persistent luminescence phosphors, and in phenomena like band gap engineering, tunnelling, photosynthesis, and thermal quenching. It is concluded that in the field of luminescence spectroscopy, thermally stimulated luminescence has proven to be an experimental technique with unique properties to study defects in solids.
... The knowledge of these parameters could help us to understand the trap structure and the physical processes inside of the material in addition to improve both accuracy and precision of many TL applications (retrospective dosimetry, dating, environmental dosimetry, etc). The methods to estimate the kinetic parameters of the phosphor is based on the kinetic analysis models (Chen and McKeever, 1997;Kitis et al., 1998;Sakurai and Gartia, 1997;Gomez-Ros et al., 2006a, 2006b, including computerized fitting of the TL glow curves considering a continuous distribution of trapping centers (Sakurai and Gartia, 1997;Gomez-Ros et al., 2006a, 2006b. Some of these methods are based on the (i) analysis of the low temperature interval of peak (initial rise method, IR); (ii) change in the peak position by means of the variable heating rate (VHR method); (iii) evolution of the position of the peak temperature (T m ) when an irradiated sample is linearly preheated up to a maximum temperature (T stop ) in the range 200-300°C.The process is successively repeated at different Tstop values. ...
... The knowledge of these parameters could help us to understand the trap structure and the physical processes inside of the material in addition to improve both accuracy and precision of many TL applications (retrospective dosimetry, dating, environmental dosimetry, etc). The methods to estimate the kinetic parameters of the phosphor is based on the kinetic analysis models (Chen and McKeever, 1997;Kitis et al., 1998;Sakurai and Gartia, 1997;Gomez-Ros et al., 2006a, 2006b, including computerized fitting of the TL glow curves considering a continuous distribution of trapping centers (Sakurai and Gartia, 1997;Gomez-Ros et al., 2006a, 2006b. Some of these methods are based on the (i) analysis of the low temperature interval of peak (initial rise method, IR); (ii) change in the peak position by means of the variable heating rate (VHR method); (iii) evolution of the position of the peak temperature (T m ) when an irradiated sample is linearly preheated up to a maximum temperature (T stop ) in the range 200-300°C.The process is successively repeated at different Tstop values. ...
... where I TL is the TL intensity, k is the Boltzmann's constant and T is the temperature. Moreover, it has been shown (Gomez-Ros et al., 2006a, 2006b) that the IR method can be also applied in case of a continuous distribution of trapping centers and in such case: ...
... The knowledge of these parameters could help us to understand the trap structure and the physical processes inside of the material in addition to improve both accuracy and precision of many TL applications (retrospective dosimetry, dating, environmental dosimetry, etc.). The methods to estimate the kinetic parameters of the phosphor is based on the kinetic analysis models (Chen and McKeever, 1997;Kitis et al., 1998;Sakurai and Gartia, 1997;Gomez-Ros et al., 2006), including computerised fitting of the TL glow curves considering a continuous distribution of trapping centres (Sakurai and Gartia, 1997;Gomez-Ros et al., 2006). Some of these methods are based on the (i) analysis of the low temperature interval of peak (initial rise method, IR); (ii) change in the peak position by means of the variable heating rate (VHR method); (iii) evolution of the position of the peak temperature (T m ) when an irradiated sample is linearly preheated up to a maximum temperature (T stop ) in the range 200-300 ºC.The process is successively repeated at different Tstop values. ...
... The knowledge of these parameters could help us to understand the trap structure and the physical processes inside of the material in addition to improve both accuracy and precision of many TL applications (retrospective dosimetry, dating, environmental dosimetry, etc.). The methods to estimate the kinetic parameters of the phosphor is based on the kinetic analysis models (Chen and McKeever, 1997;Kitis et al., 1998;Sakurai and Gartia, 1997;Gomez-Ros et al., 2006), including computerised fitting of the TL glow curves considering a continuous distribution of trapping centres (Sakurai and Gartia, 1997;Gomez-Ros et al., 2006). Some of these methods are based on the (i) analysis of the low temperature interval of peak (initial rise method, IR); (ii) change in the peak position by means of the variable heating rate (VHR method); (iii) evolution of the position of the peak temperature (T m ) when an irradiated sample is linearly preheated up to a maximum temperature (T stop ) in the range 200-300 ºC.The process is successively repeated at different Tstop values. ...
... This method is based on the hypothesis that occupancies of the relevant states remain almost constant for the lowest temperature side of the TL peak and, consequently, this side of the peak will follow an exponential dependence regardless of the kinetic order and the applicability of the quasiequilibrium approximation (Chen and McKeever, 1997;Gonzalez et al., 2013), thus giving a temperature dependence I TL (T<<TM) α exp (-E/kT), where I TL is the TL intensity, k is the Boltzmann´s constant and T is the temperature. Moreover, it has been shown (Gomez-Ros et al., 2006) that the IR method can be also applied in case of a continuous distribution of trapping centers and in such case: ...
Pumiceis a natural Si-rich material displaying a complex cathodo- (CL) and thermoluminescence (TL) glow curves. The UV-IR CL emission consists of (i) a UV waveband in the range of 340-420 nm,(ii) blue band at 450-480 nmand (iii) a broad emission in the green-red region (at 550-650 nm)that could be respectively linked to (Non Bridging Oxygen Hole Centres, ≡ Si–O•), self-trapped excitons and point defects (Mn2+−0.03%-and Fe −1.15%-).Thermal treatments performed on the TL glow curves allowed us to determine that the trap system could be associated with a continuum in the trap distribution, since successive thermal pretreatments in the range of 200-310 °C induce an emission that shifts linearly to higher temperatures when the thermal pretreatment (Tstop) is increased, while the intensity of the maxima decreases similarly to the peak area. The evaluation of the Ea values, s value and the trap system calculated by VHR, IR and Glow curve fitting methods considering three possible distribution function for n(E): gaussian, exponential and uniform, has given matching values for the 280 °C TL peak.
