Vasilis Pagonis

Thermally and optically stimulated luminescence : a simulation approach

About the Authors . Preface. Acknowledgements. 1 Introduction. 1.1 The Physical Mechanism of TL and OSL Phenomena. 1.2 Historical Development of TL and OSL Dosimetry. 1.3 Historical Development of Luminescence Models. 2 Theoretical Basis of Luminescence Phenomena. 2.1 Energy Bands and Energy Levels in Crystals. 2.2 Trapping Parameters Associated with Impurities in Crystals. 2.3 Capture Rate Constants. 2.4 Thermal Equilibrium. 2.5 Detailed Balance. 2.6 Arrhenius Model. 2.7 Rate Equations in the Theory of Luminescence. 2.8 Radiative Emission and Absorption. 2.9 Mechanisms of Thermal Quenching in Dosimetric Materials. 2.10 A Kinetic Model for the Mott Seitz Mechanism in Quartz. 2.11 The Thermal Quenching Model for Alumina by Nikiforov et al. 3 Basic Experimental Measurements. 3.1 General Approach to TL and OSL Phenomena. 3.2 Excitation Spectra. 3.3 Emission Spectra. 3.4 Bleaching of TL and OSL. 4 Thermoluminescence: The Equations Governing a TL Peak. 4.1 Governing Equations. 4.2 One Trap-One Recombination Center (OTOR) Model. 4.3 General-order Kinetics. 4.4 Mixed-order Kinetics. 4.5 Q and P Functions. 4.6 Localized Transitions. 4.7 Semilocalized Transition (SLT) Models of TL. 5 Basic Methods for Evaluating Trapping Parameters. 5.1 The Initial-rise Method. 5.2 Peak-shape Methods. 5.3 Methods of Various Heating Rates. 5.4 Curve Fitting. 5.5 Developing Equations for Evaluating Glow Parameters. 5.6 The Photoionization Cross Section. 6 Additional Phenomena Associated with TL. 6.1 Phosphorescence Decay. 6.2 Isothermal Decay of TL Peaks. 6.3 Anomalous Fading and Anomalous Trapping Parameters of TL. 6.4 Competition Between Excitation and Bleaching of TL. 6.5 A Model for Mid-term Fading in TL Dating Continuum of Traps. 6.6 Photo-transferred Thermoluminescence (PTTL). 6.7 TL Response of Al2O3:C to UV Illumination. 6.8 Dependence of the TL Excitation on Absorption Coefficient. 6.9 TL Versus Impurity Concentration Concentration Quenching. 6.10 Creation and Stabilization of TL Traps During Irradiation. 6.11 Duplicitous TL Peak due to Release of Electrons and Holes. 6.12 Simulations of the Duplicitous TL Peak. 7 Optically Stimulated Luminescence (OSL). 7.1 Basic Concepts of OSL. 7.2 Dose Dependence of OSL Basic Considerations. 7.3 Numerical Results of OSL Dose Dependence. 7.4 Simulation of the Dose-rate Dependence of OSL. 7.5 The Role of Retrapping in the Dose Dependence of POSL. 7.6 Linear-modulation OSL (LM-OSL). 7.7 Unified Presentation of TL, Phosphorescence and LM-OSL. 7.8 The New Presentation of LM-OSL Within the OTOR Model. 7.9 TL-like Presentation of CW-OSL in the OTOR Model. 7.10 Dependence of Luminescence on Initial Occupancy OTOR Model. 7.11 TL Expression Within the Unified Presentation. 7.12 Pseudo LM-OSL and OSL Signals under Various Stimulation Modes. 7.13 OSL Decay and Stretched-exponential Behavior. 7.14 Optically Stimulated Exoelectron Emission. 7.15 Simulations of OSL Pulsed Annealing Techniques. 8 Analytical and Approximate Expressions of Dose Dependence of TL and OSL. 8.1 General Considerations. 8.2 Competition During Excitation. 8.3 Competition During Heating. 8.4 The Predose (Sensitization) Effect. 8.5 Sensitization and De-sensitization in Quartz. 8.6 Dose-rate Dependence. 8.7 Sublinear Dose Dependence of TL and LM-OSL in the OTOR System. 8.8 Dose-dependence and Dose-rate Behaviors by Simulations. 8.9 Simulations of the Dose-rate Effect of TL. 8.10 Nonmonotonic Dose Dependence of TL and OSL. 8.11 Nonmonotonic Dose Dependence of TL Simulations. 8.12 Nonmonotonic Effect of OSL Results of Simulations. 9 Simulations of TL and OSL in Dating Procedures. 9.1 The Predose Effect in Quartz. 9.2 Simulation of Thermal Activation Characteristics in Quartz. 9.3 The Bailey Model for Quartz. 9.4 Simulation of the Predose Dating Technique. 9.5 The Single Aliquot Regenerative Dose (SAR) Technique. 9.6 Thermally Transferred OSL (TT-OSL). 10 Advanced Methods for Evaluating Trapping Parameters. 10.1 Deconvolution. 10.2 Monte-Carlo Methods. 10.3 Genetic Algorithms. 10.4 Application of Differential Evolution to Fitting OSL Curves. 11 Simultaneous TL and Other Types of Measurements. 11.1 Simultaneous TL and TSC Measurements Experimental Results. 11.2 Theoretical Considerations. 11.3 Numerical Analysis of Simultaneous TL-TSC Measurements. 11.4 Thermoluminescence and Optical Absorption. 11.5 Simultaneous Measurements of TL and ESR (EPR). 11.6 Simultaneous Measurements of TL and TSEE. 12 Applications in Medical Physics. 12.1 Introduction. 12.2 Applications of Luminescence Detectors in Medical Physics. 12.3 Examples of in-vivo Dosimetric Applications. 12.4 Radioluminescence. 13 Radiophotoluminescence. 13.1 Development and Use of RPL Materials. 13.2 The Simplest RPL Model. 14 Effects of Ionization Density on TL response. 14.1 Modeling TL Supralinearity due to Heavy Charged Particles. 14.2 Defect Interaction Model. 14.3 The Unified Interaction Model. 15 The Exponential Integral. 15.1 The Integral in TL Theory. 15.2 Asymptotic Series. 15.3 Other Methods. Previous Books and Review Papers. Appendix A Examples. A.1 Simulation of OSL Experiments Using the OTOR Model. A.2 Simulation of OSL Experiments Using the IMTS Model. A.3 Simulation of TL Experiment Using the Bailey Model. References. Author Index. Subject Index.

Applicability of the Zimmerman predose model in the thermoluminescence of predosed and annealed synthetic quartz samples

Abstract The “110°C” thermoluminescence (TL) peak of unfired synthetic quartz is known to exhibit a highly superlinear growth with absorbed dose. In this paper, it is shown that the well-known Zimmerman predose model can explain recent experimental results on the superlinearity of annealed synthetic quartz, as well as experimental results on the superlinearity of heavily predosed samples at room temperature. In the case of the predosed samples, the simulation solves the kinetic rate equations for the various stages in the experimental TL predose process. The results of the simulation explain the behavior of the TL versus dose curves at different predoses, as well as the detailed behavior of the superlinearity coefficient k as a function of the predose amount. In the case of the annealed samples, the simulation solves the kinetic equations for different values of the initial concentration of holes in the recombination center. The results of the simulation explain the behavior of the TL versus dose curves at different annealing temperatures, as well as the detailed behavior of the superlinearity coefficient k in each of the two distinct superlinearity regions. The simulation also produces the correct order of magnitude for the large sensitivity changes of the TL intensity observed in both sets of experiments.

A model for non-monotonic dose dependence of thermoluminescence (TL)

In the applications of thermoluminescence (TL) in dosimetry and archaeological and geological dating, a desirable dose dependence of TL intensity is a monotonically increasing function, preferably linear. It is well known that in many dosimetric materials, nonlinear dependence is observed. This may includ eas uperlineardependence at low doses and/or sublinear dose dependence at higher doses, where the TL intensity approaches saturation. In quite a number of materials, non-monotonic dose dependence has been observed, namely, the TL intensity reached a maximum value a ta certain dose and decreased at higher doses. This effect is sometimes ascribed to ‘radiation damage’ in the literature. In the present work we show, both quasi-analytically and by using numerical simulation, that such dose dependence may result from a simple energy level scheme of at least one kind of trapping state and two kinds of recombination centres. One does not necessarily have to assume a destruction of trapping states or recombination centres at high doses. Instead, the main concept involved is that of competition which takes place both at the excitation stage and the readout stage during the heating of the sample. This may explain the fact that the phenomenon in question, although very often ignored, is rather common. Cases are identified in which competition during excitation dominates, and others in which competition during read-out dominates.

Modelling thermal transfer in optically stimulated luminescence of quartz

A previously published kinetic model for the production of luminescence signals in quartz is used to investigate the production of thermally transferred optically stimulated luminescence (TT-OSL) signals. This paper provides a mathematical description of the thermal transfer mechanism for two different phenomena that have been observed in previously published experiments (Aitken and Smith 1988 Quat. Sci. Rev. 7 387–93). The starting point is the model proposed by Bailey (2001 Radiat. Meas. 33 17–45). The numerical values of some of the parameters are varied so that they match the experimental data. The effect caused by varying these values is investigated. The first of these phenomena takes place after storing optically bleached samples at room temperature; this involves the traps responsible for the 110 ◦ C thermoluminescence (TL) peak of quartz acting as a refuge trap. The second phenomenon concerns OSL signals that are induced by heating the samples after the bleaching of the OSL signal and involves a putative TL peak at ∼230 ◦ C associated with the refuge trap; specifically, the paper presents a simulation of the temperature dependence of the OSL signal measured by successively heating the quartz samples to higher temperatures up to ∼400 ◦ C.

Annealing effects on the thermoluminescence of synthetic calcite powder

Abstract We have studied the effect of annealing temperature on the nature and the kinetics of the thermoluminescence (TL) trapping centers of synthetic calcite. Samples of high purity calcite powder were annealed in air and in the temperature range 300–700°C. The samples were subsequently irradiated and the effect of the annealing on the TL of the samples was studied using several techniques. The energy values for the traps associated with the observed TL peaks were measured using the initial rise method and were used as input for a least-squares fit procedure, which expresses the TL glow curves as the sum of five individual peaks of general order kinetics. It was found that all the experimental TL glow curves for different annealing temperatures and various doses could be fitted to the same set of kinetic parameters E , s and b indicating that the annealing process probably does not change the nature of the trapping centers. The first- and second-glow TL growth curves were measured for four TL peaks and were fitted to equations of the form y = y ∞ (1 − exp(-β t )), where t is the irradiation time. The value of the growth constant, β, was found to be independent of the annealing temperature for at least two of the TL peaks studied and for annealing temperatures up to 600°C. The activation energy for the charge in sensitivity with annealing temperature was found using Arrhenius-type plots for each TL peak. Our results can be explained with an energy scheme similar to the one used in the predose model of quartz; according to this model the change of sensitivity to ionizing radiation observed after annealing is due to changes occuring within the luminescence centers while the trapping centers remain unaffected. Annealing in air for temperatures at or above 700°C caused a collapse in the TL sensitivity, in agreement with the energy scheme of the predose model.

Kinetic analysis of thermoluminescence glow curves in feldspar: evidence for a continuous distribution of energies

The thermoluminescence (TL) glow curves from feldspars have been the subject of numerous studies, because of their importance in luminescence dating and dosimetry. This paper presents new experimental TL glow curves in a plagioclase feldspar, measured using the Tmax-Tstop technique of glow curve analysis. Kinetic analysis of the experimental results is carried out for a freshly irradiated sample, as well as for a sample which has undergone optical treatment using infrared light for 100 s at 50°C. Application of the initial rise method of analysis indicates that the TL signals from both samples can be characterized by a continuous distribution of energy levels. By subtracting the TL glow curves measured at successive Tstop values, a series of TL glow curves is obtained which are analyzed using the empirical general order kinetics. It is found that all TL glow curves obtained by this subtractive procedure can be described accurately by the same general order parameter b ∼1.7. In a second attempt to analyze the same TL glow curves and possibly extract information about the underlying luminescence process, the shape of TL glow curves is analyzed using a recently proposed physical kinetic model which describes localized electronic recombination in donor-acceptor pairs. Within this model, recombination is assumed to take place via the excited state of the donor, and nearest-neighbor recombinations take place within a random distribution of centers. This recent model has been used recently to describe successfully several types of luminescence signals. This paper shows that it is possible to obtain good fits to the experimental data using either one of these two approaches.

Radioluminescence in Al2O3 : C – analytical and numerical simulation results

The phenomenon of radioluminescence (RL) has been reported in a number of materials including Al2O3 : C, which is one of the main dosimetric materials. In this work, we study RL using a kinetic model involving two trapping states and two kinds of recombination centres. The model has been previously used to provide a quantitative description of the thermoluminescence and optically stimulated luminescence processes in Al2O3 : C. Using appropriate sets of trapping parameters for the kinetic model, the RL signal along with the occupancies of the relevant traps and centres are simulated numerically. The set of differential equations is also solved analytically by assuming dynamic balance during sample irradiation. Analytical expressions are obtained for the concentrations of traps and centres in the material during irradiation with short irradiation pulses, by assuming that quasi-steady conditions hold during irradiation. Several experimentally observed characteristics of the RL signals are explained by using the model. Good quantitative agreement is found between the analytical expressions and the numerical solutions of the model for short irradiation pulses.

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.

Thermoluminescence study of annealing a geological calcite

Abstract Annealing of calcite prior to measuring second-glow TL growth curves is an important part of TL dating of calcite. That large changes in TL sensitivity to ionizing radiation are sometimes brought about by annealing is well documented. Annealing studies of two samples of a geological calcite revealed that TL peaks in the violet region of the spectrum (300–450 nm wavelength) and one in the orange region (≈590 nm) grew in sensitivity with annealing temperature up to some limiting temperature, depending on the TL peak. Upon annealing above this limiting temperature the peak disappeared. These effects were not reversible. The presence of an elevated CO 2 partial pressure in the annealing atmosphere enhanced the sensitivity of at least one violet TL peak, at ≈240°C.

Dissolution and subsequent re-crystallization as zeroing mechanism, thermal properties and component resolved dose response of salt (NaCl) for retrospective dosimetry

In the present study we report dosimetric properties of iodized salt aiming at using it as an accidental luminescent dosimeter. It was found that the very good sensitivity of its main dosimetric peak is strongly affected by thermal treatments. This is also the case for OSL emission. The sensitivity loss due to heating implies that caution should be exercised while applying single aliquot protocols for dose evaluation. The sequence of dissolution and subsequent re-crystallization was established to be an extremely effective zeroing mechanism for the TL signal. The linearity in the dose response was also monitored in the case of dissolved and subsequently re-crystallized salt. In the case of naturally occurring salt, zeroing of the TL signal due to dissolution as well as the linearity of dose response up to doses as large as 100 Gy were found to be very promising features for dating applications.