An improved experimental procedure of separating a composite thermoluminescence glow curve into its components

We present an improved experimental procedure of separating a composite thermoluminescence glow curve into its components. Careful monitoring of the isothermal cleaning process using the initial rise method ensures the complete thermal removal of TL peaks. Digital subtraction of two experimental TL glow curves yields individual experimental TL glow peaks. Several standard methods (initial rise and whole glow curve) are used to obtain the energy values and frequency factors of the traps. The method has been used successfully to analyze the well-known composite TL glow curve of the dosimetric material LiF (TLD-100). The limitations of the method are illustrated by analyzing the highly complex TL glow curve of a UV irradiated synthetic calcite consisting of at least 6 TL peaks. Although the method works best for TL glow curves described by first order kinetics, it should also be applicable to more general kinetics.     

Monte-Carlo method for determining the quenching function from variable heating rate measurements

In thermoluminescence (TL) measurements radiative recombination takes place at various temperatures. Typically, the quantum efficiency of luminescence decreases with increasing temperature. We call this mechanism the thermal quenching. There is no simple method to ‘restore’ unquenched TL data. This paper presents an algorithm, based on the Monte-Carlo method, for calculating the quenching function and restoring the unquenched TL curve. For this purpose we use a series of TL glow curves measured at the same initial conditions with variable heating rates. The method is quite general and no particular kinetic model of TL need to be assumed. The reliability of the method is tested using computer generated TL glow curves obeying the simple trap model (STM) kinetics.     

A new method for the numerical analysis of thermoluminescence glow curve

A new method to analyze the thermoluminescence (TL) glow curve has been presented. It has been shown that this method is efficient and fast in generating the TL glow curves and can be adopted in a numerical curve fitting for obtaining the relevant TL parameters of a given TL glow curve data. This new method is based on a general approximation (GA) which assumes only that the concentration of the electrons in the conduction band is negligible when compared with the concentration of the electrons in the traps. The GA method has been tested against the reference glow curve data which was generated by the full iteration method without any prior approximation in the one-trap-one-recombination-centre model. By finding the best fit between the reference data and the curves generated by the GA method, the values of the kinetics parameters have been determined. Also, the general order kinetics (GOK) and the peak shape method have been examined. The fitted values of the activation energy and the initial concentration of electron by the GA method match reasonably well with the original value.     

Thermoluminescence Kinetic Parameters of TLD-600 and TLD-700 after ~(252)Cf Neutron+Gamma and ~(90)Sr-~(90)Y Beta Radiations

The thermoluminescent(TL) properties such as glow curve structure, relative thermoluminescence sensitivity,dose response linearity of lithium fluoride thermoluminescent dosimeters 6 LiF:Ti,Mg(TLD-600) and 7 LiF:Ti,Mg(TLD-700) are investigated after irradiation ~(252)Cf neutron+gamma and ~(90)Sr-~(90)Y beta sources at room temperature and then the obtained results are compared. The kinetic parameters, namely the order of kinetics b,activation energy Ea and the frequency factor s,are calculated using the computerized glow curve deconvolution(CGCD) program. The effect of heating rate on the glow curves of dosimeters is also investigated. The maximum TL peak intensities and the total area under the glow curves decrease with the increasing heating rate. There is no agreement with the kinetic parameters calculated by the CGCD program for both radiation sources.     

Thermoluminescence glow curve deconvolution of LiF:Mg,Cu,Si with more realistic kinetic models

Thermoluminescence (TL) glow curves of LiF:Mg,Cu,Si were deconvoluted with the introduction of enhanced physical model which envisages that both electrons and holes, produced by ionization radiation and trapped at the respective traps, can be thermally released into the conduction and the valence band, respectively and the holes may also radiatively recombine with electrons at the electron recombination centers. The model is more generalized than the ordinary trap interaction model which only permits the traffic of electrons through the conduction band. An effective numerical analysis method was developed to calculate the glow curve to be compatible with the measured curves. The validity of the numerical method was verified through artificially generated TL glow curves for a wide range of trap parameters. In order to identify TL kinetics of LiF:Mg,Cu,Si with higher accuracy, its glow curves were deconvoluted for two more generalized models, namely, the Schön–Klasens model and the Chen–Pagonis–Lawless model as well as the ordinary trap interactive model. The parameters in the more generalized multi-trap multi-recombination center (MTMR) model were found to be consistent with the quasi-static approximation(QSA) method.     

The validity of the two heating rates method to obtain the trapping parameters from general-order thermoluminescence glow peaks

The two heating rates method, which is usually known as Booth-Bohun method, is currently employed for obtaining the activation energy E (eV) of first-order thermoluminescence (TL) glow peak. However, this method can be used for obtaining the activation energy for all types of TL glow peaks irrespective of their order of kinetics (b). The present work shows that the condition of maximum intensity of first-order kinetics can be safely used to obtain the pre-exponential factor S″ (s⁻¹) in the case of general-order glow peak when Booth-Bohun method was used to obtain E. Also, the present work suggests a numerical method for obtaining the order of kinetic (b) of general-order glow peak. This method depends on the activation energy E obtained by Booth-Bohun method and the suggested method mentioned above to obtain S″. An independent evaluation of the suggested methods is illustrated here by taken some numerically computed glow peaks by applying the one-trap and one-recombination-center (OTOR) model.     

Thermoluminescence in systems not subject to the usual approximations for first and second order kinetics

The properties of thermoluminescence (TL) glow curves have been studied in systems, containing one or more glow peaks, not restricted to the assumptions used to derive the usual first and second order glow peak kinetic expressions. If retrapping is negligible first order glow peaks are obtained whose peak temperature and shape are independent of other factors such as initial trapped charge concentrations. If retrapping occurs, glow peaks are obtained that are, in most cases, only approximated by first or second order kinetics. Also, in these cases the peak temperature, shape, relative intensity and other glow curve characteristics depend strongly on initial trapped charge concentrations, recombination and retrapping cross sections and other factors.     

Applications of the three points analysis method for obtaining the trap parameters and the separation of thermoluminescence glow curve into its components

Here, we apply a recently developed technique to separate a composite thermoluminescence (TL) glow curve into its individual components and to evaluate the trap parameters of the individual TL glow peaks. These parameters include the order of kinetics b, the activation energy E (eV) and the frequency factor S (s^?1) or the pre-exponential factor S″ (s^?1). Recently, a general equation was developed to estimate the order of kinetics b. The characteristic point of this equation is that any set of three data points in a TL glow curve can yield b. Using this characteristic, an improved procedure was suggested to separate a composite glow curve, which includes several overlapping peaks, into its individual components and to obtain the trap parameters of the individual glow peaks. The method was applied here to analyze and determine the trap parameters of the TL glow curve of the promising TL dosimetric material, double potassium yttrium fluoride (K₂YF₅) doped with praseodymium ions (Pr³⁺), in response to γ-irradiation.     

Reconstruction of thermally quenched glow curves in quartz

The experimentally measured thermoluminescence (TL) glow curves of quartz samples are influenced by the presence of the thermal quenching effect, which involves a variation of the luminescence efficiency as a function of temperature. The real shape of the thermally unquenched TL glow curves is completely unknown. In the present work an attempt is made to reconstruct these unquenched glow curves from the quenched experimental data, and for two different types of quartz samples. The reconstruction is based on the values of the thermal quenching parameter W (activation energy) and C (a dimensionless constant), which are known from recent experimental work on these two samples. A computerized glow-curve deconvolution (CGCD) analysis was performed twice for both the reconstructed and the experimental TL glow curves. Special attention was paid to check for consistency between the results of these two independent CGCD analyses. The investigation showed that the reconstruction attempt was successful, and it is concluded that the analysis of reconstructed TL glow curves can provide improved values of the kinetic parameters E, s for the glow peaks of quartz. This also leads to a better evaluation of the half-lives of electron trapping levels used for dosimetry and luminescence dating.     

α-Al2O3单晶的热释光和光释光特性

研究了纯α-Al₂O₃单晶的热释光发光曲线和三维发光谱，以及光释光衰变曲线，对它们的发光机理和剂量学特性进行了分析和讨论.实验观察到α-Al₂O₃单晶β射线照射后立即测量的热释光发光曲线，有峰温为76℃和207℃两个发光峰.经γ射线照射数小时后测量的三维发光谱，只有峰温207℃波长为416 nm发光峰，它与α-Al₂O₃:C晶体的发光波长基本相同，是受热激发到导带的电子与F< 关键词： 2O₃')" href="#">α-Al₂O₃ 三维发光谱 TL/OSL剂量响应     

Thermoluminescence glow curve involving any extent of retrapping or any order of kinetics

Adirovitch set of equations has been modified to explain the mechanisms involved in thermoluminescence (TL) glow curve. A simple model is proposed which explains the occurrence of TL glow curve involving any extent of retrapping or any order of kinetics. It has been observed that the extents of recombination and simultaneous rewrapping decide the order of kinetics involved. TL decay parameters, order of kinetics and initial concentration of trapped electrons per unit volume are evaluated easily and conveniently. It has been observed that retrapping increases with increasing order of kinetics.     

Effects of 60Co gamma-ray irradiation on the optical properties of natural and synthetic quartz from 85 to 300 K

Optical absorption and luminescence measurements have been made between 85 and 300 K on natural and synthetic quartz during and after ⁶⁰Co gamma-ray irradiation. Absorption vs. dose curves can be resolved into the sum of a saturating exponential and a linear component. At 85 K the slope of the linear component is small, while at 300 K the linear term dominates the growth curves. The coloring induced by irradiation at 85 K decreased in a complex manner during anneal at a linear rate to 300 K. During this annealing process multiple-peak thermoluminescent (TL) glow curves were observed and recorded. The TL emission spectra are described accurately by single Gaussian-shaped bands, whereas the gamma-ray induced luminescence is comprised of several poorly resolved bands. All recorded TL glow curves are characterized by a set of four first order glow peaks between 150 and 220 K. The temperature dependence of radioluminescence intensity is described by a classical model in which a temperature-independent radiative transition competes with a thermally activated non-radiative process.     

Development of a new curve deconvolution algorithm for optically stimulated luminescence

A new computerized glow curve deconvolution (CGCD) algorithm for thermoluminescence(TL) and optically stimulated luminescence (OSL) is presented. The proposed approach can be adopted in a numerical curve fitting for obtaining the relevant trapping parameters of a set of glow data taken with both thermal and optical stimulation. This method is based on the one trap one recombination center (OTOR) model with minimal simplifying assumptions. To demonstrate the ability of the method, a new computer program has been developed and tested with some synthetic OSL data.     

Study of the glow curve structure of the minerals separated from black pepper (Piper nigrum L.)

The inorganic mineral fraction extracted from black pepper (Piper nigrum L.) has been analysed using a thermoluminescence (TL) method, investigating the glow curve structure, including an evaluation of the kinetic parameters. Different grain sizes, i.e. 10, 74, and 149 μm, were selected from commercial black pepper. The X-ray diffraction of the inorganic fraction shows that quartz is the main mineral present in it. The samples were exposed to 1–25 kGy doses by gamma rays of ⁶⁰Co in order to analyse the thermally stimulated luminescence response as a function of the delivered dose. The glow curves show a complex structure for different grain sizes of the pepper mineral samples. The fading of the TL signal at room temperature was obtained after irradiation, and it was observed that the maximum peaks of the glow curves shift towards higher values of the temperature when the elapsed time from irradiation increases. It seems that the fading characteristic may be related to a continuous trap distribution responsible for the complex structure of the glow curve. Similar glow curves structure behaviour was found under ultraviolet irradiation of the samples. The activation energy and the frequency factor were determined from the glow curves of different grain sizes using a deconvolution programme because of the evident complexity of the structure.     

Determination of thermoluminescence kinetic parameters of thulium doped lithium calcium borate

For the first time kinetic parameters of thulium doped Lithium calcium borate (LCB) Thermoluminescence (TL) material are reported here. Irradiated LCB:Tm³⁺ powder has revealed two intense TL glow peaks one at 510 (peak 1) and the other at 660 K (peak 2). Activation energy (E), frequency factor (s) and order of kinetics (b) of these peaks were determined by various heating rate (VHR), initial rise (IR), and peak shape (PS) methods. The trap depth and frequency factor determined for peaks 1 and 2 of LCB:Tm phosphor using VHR and IR methods are in good agreement. The average activation energy of peaks 1 and 2 obtained by these methods is 1.62 and 1.91 eV respectively. The frequency factors of peaks 1 and 2 are in the range of 10^13–16 and 10^12–14 sec⁻¹ respectively. The E and s values estimated using the glow peak shape dependent parameters are relatively less compared to the values obtained from other methods. The large difference in these values is due to the complex nature of the glow curves. The order of the kinetics process for complex glow curve peaks could not be assigned on the basis of shape parameters alone but T_m response on absorbed dose is to be considered for final confirmation. Glow peaks 1 and 2 of LCB:Tm³⁺ obey first and general order kinetics respectively.     

Two-point method for kinetic analysis of a thermoluminescence glow peak

We present a method for the estimation of defect (trap) physical parameters from thermoluminescence (TL) glow peaks. In this method, the order of kinetics b is determined using two values of TL intensity each of which corresponds to the same temperature (T ₁) on two separate glow peaks of a phosphor. The two glow peaks are obtained from two aliquots of the phosphor irradiated to same dose but read out at different heating rates. The proposed method requires a minimum of only two data points in contrast to standard peak shape (PS) methods that require three points corresponding to three different temperatures on the same glow peak. Once the order of kinetics b is determined, the activation energy E is calculated by taking a second point (T ₂) on any one of the two glow peaks. The values of b and E thus obtained are used to evaluate the frequency factor S ^′′ and the number of trapped electrons before the heating begins n _o. The validity of the method was checked using two numerically generated glow peaks. For the two cases, the method reproduced the input values reasonably well. The method was also used to analyse two experimental glow peaks. The results obtained provide a reasonably good fit to the experimental data. The kinetic parameters calculated using the present technique are comparable to those calculated using PS and initial rise methods. Initial guesses can easily be obtained for E and S ^′′ using the present technique when a glow curve is to be deconvoluted with a model consisting of many unknown parameters with E and S″ inclusive.     

Thermally stimulated luminescence studies of undoped,Cu- and Mn-doped CaSO4 compounds

Thermally stimulated luminescence (TSL) of undoped and doped CaSO₄ with activators such as Cu and Mn has been investigated. The polycrystalline samples of undoped and doped CaSO₄ are prepared by the melting method. The formation of CaSO₄ compound is confirmed by X-ray diffraction and Fourier transform infrared studies. Scanning electron microscopic studies of CaSO₄ are also carried out.

The TSL glow curves of undoped CaSO₄, Cu- and Mn-doped CaSO₄ are studied. Comparison of the thermoluminescence (TL) intensity of the most intensive glow peak of Cu-doped CaSO₄ compound with that of undoped CaSO₄ shows that addition of Cu impurity in CaSO₄ compound enhances the TL intensity by about four times. However, the addition of Mn impurity to undoped CaSO₄ increases the TL intensity by about three times when compared with that of undoped CaSO₄. The TL-dose dependence of all three samples was studied and was observed to be almost linear in the studied range of irradiation time. Among the samples studied, namely undoped CaSO₄ and Cu- and Mn-doped CaSO₄, Cu-doped CaSO₄ is found to be the most sensitive. The trap parameters, namely order of kinetics (b), activation energy (E) and frequency factor (s) associated with the most intensive glow peaks of CaSO₄:Mn, CaSO₄:Cu and CaSO₄ phosphors were determined using the glow curve shape (Chen's) method.     

Investigation of the trap state of Sr2MgSi2O7: Eu2+, Dy3+ phosphor and decay process

The thermoluminescence glow curves of Sr₂MgSi₂O₇: Eu²⁺, Dy³⁺ phosphor were measured after various delay times. A single trap center is confirmed that conforms to a kinetics model with order greater than 1, leading to a suppression of TL intensity and a high temperature shift of the TL peak with longer delay times. A constant trap depth supports this phenomenon. Further, the decay curve of the afterglow and the change in initial trapped carrier concentration can be fitted using general-order kinetics and the fitting results show that the afterglow is close to a second-order kinetics process, which implies that most of the released carriers are retrapped.     

A preliminary approach to identify irradiated foods by thermoluminescence measurements

Thermoluminescence (TL) is one of the physical methods for the identification of irradiated foods. Among the currently developed methods, TL is the most widely used method for the identification of irradiated foods. However, in order to use this method, silicate minerals should be isolated from food samples. The process for the isolation of silicate minerals is time consuming and laborious. In this work, we have investigated the applicability of the TL method using iron-containing minerals instead of silicate minerals. In the TL analyses of dried spices, TL glow curves of iron-containing minerals showed maximum temperatures between 150 and 250 °C which were the same as those of silicate minerals. The process for the mineral separation of the proposed method is simple, fast, easy, and reliable. Moreover, the analysis results including TL ratio have not shown significant differences compared with the silicate minerals method. As a result, the TL measurements using the iron-containing minerals could be an excellent method for the identification of the irradiated foods, including dried spices.     

Thermoluminescence in two varieties of jadeite: Irradiation effects and application to high dose dosimetry

The thermoluminescence properties of white (WJ) and green (GJ) mineral jadeite have been investigated with a view to be of use in high dose dosimetry. WJ presented glow curve with 110, 190 and 235 °C peaks. All these peaks grow with radiation dose. The glow curve of GJ the green variety has TL peaks at 140, 210, 250 and 330 °C. We also observed that there is a difference between the TL glow curves for both samples, irradiated with gamma and electron. As expected the green jadeite can be used for measurement of dose as high as 50 kGy.