Non-empirical peak shape methods based on the physical model of the one trap one recombination center model.

Any experimental Thermoluminescent (TL) glow-peak contains the activation energy information of its corresponding energy level within the band gap in insulating materials. The theory of peak shape methods (PSM) correlates the macroscopic geometrical characteristics of a single TL peak with activation energy of the level responsible for the TL peak by assuming that the area under a TL peak can be approximated by the area of a triangle. In this way the geometrical characteristics becomes the measure of the activation energy. In the present work new PSM expressions are derived, which are not empirical as the existing ones but are based of the physical model of one trap one recombination (OTOR) center. Three cases are considered. (I) Delocalized OTOR for re-trapping probability smaller than the recombination probability. (II) Delocalized OTOR for re-trapping probability greater than recombination probability. (III) Localized transitions OTOR model. The system of differential equations of each case model were solved analytically using the Lambert W function (or equivalently the Wright ω function). Then the resulted analytical expressions of TL intensity as a function of temperature were used to derive new PSM. The new PSM from all cases are formally exactly the same, having, however, strong differentiation in their coefficients. The functionality of the new expressions is tested and its comparison with pre-existing PSM is performed.

On the Need for Deconvolution Analysis of Experimental and Simulated Thermoluminescence Glow Curves.

Simulation studies of thermoluminescence (TL) and other stimulated luminescence phenomena are a rapidly growing area of research. The presence of competition effects between luminescence pathways leads to the complex nature of luminescence signals, and therefore, it is necessary to investigate and validate the various methods of signal analysis by using simulations. The present study shows that in simulations of luminescence signals originating from multilevel phenomenological models, it is not possible to extract mathematically the individual information for each peak in the signal. It is further shown that computerized curve deconvolution analysis is the only reliable tool for extracting the various kinetic parameters. Simulation studies aim to explain experimental results, and therefore, it is necessary to validate simulation results by comparing with experiments. In this paper, testing of simulation results is performed using two methods. In the first method, the influence of competition effects is tested by comparing the input model parameters with the output values from the deconvolution analysis. In the second method, the agreement with experimental results is tested using the properties of well-known glow peaks with very high repeatability among TL laboratories, such as the 110 °C glow peak of quartz.

Thermoluminescence glow-curve deconvolution using analytical expressions: A unified presentation.

This study provides a unified presentation of thermoluminescence (TL) glow-curve deconvolution within the framework of the open source R package "tgcd", according to various analytical expressions that describe first-, second-, general-, and mixed-order kinetics as well as the recently developed semi-analytical expressions that derive from the one trap-one recombination center (OTOR) model that utilizes the Lambert W function or the Wright Omega function. We provide a comprehensive, flexible, convenient, and openly accessible program to analyze TL glow curves according to different models and expressions. The consistency of kinetic parameters determined using different model expressions was assessed using measured TL glow curve of CaF2:Dy. The performance of the computerized glow curve deconvolution (CGCD) method was also tested using simulated glow curves. Results revealed the benefits of comparing kinetic parameters determined from different model expressions and those obtained using experimental TL evaluation methods to assess the reliability of deconvolution results. The accuracy of the CGCD method is dependent upon both the model expressions used and the intrinsic trapping parameters of the TL material.

Study of dental zirconia reinforced lithium silicate for its use as a personal accidental dosimeter.

A recently introduced material for dental restorations, Zirconia reinforced Lithium Silicate (ZLS), is examined for its properties, in order to be used as a personal accidental thermoluminescence dosimeter. For this purpose, its main thermoluminescence characteristics are studied, such as its sensitivity, signal reproducibility, fading, dose response and lower detectable dose limit. Furthermore, the material is characterized by means of microscopic, spectroscopic and crystallographic techniques. The results propose that ZLS is promising to be used as a personal accidental thermoluminescence dosimeter for post-irradiation detection, with single aliquot protocols.

Stimulated luminescence emission: From phenomenological models to master analytical equations.

This paper reviews developments in phenomenological models of stimulated luminescence phenomena. A set of five master equations is presented, which describe a wide variety of stimulated luminescence signals: thermoluminescence, isothermal luminescence, optically stimulated luminescence and infrared stimulated luminescence. Both delocalized and localized models are reviewed, and analytical solutions are presented for these models. The master equations are tested against the solutions of the differential equations in the models, as well by fitting experimental data for a variety of luminescencent dosimetric materials. Three out of the five master equations involve the Lambert W(z) function, thus establishing this function as the theoretical cornerstone of the phenomenological luminescence models. The applicability of the superposition principle is discussed, in connection with computerized curve deconvolution analysis.

Thermoluminescence characteristics of a chondrite (Holbrook) and an aubrite achondrite (Norton County) meteorites.

The present study constitutes the first part of a meteorite project, currently in progress, towards the full and thorough dosimetric study (TL and OSL) of two different meteorites of recent fall, Norton County and Holbrook. Both meteorites exhibit strong TL sensitivity, linear dose response and no saturation for doses up to 2kGy. However, the two meteorites exhibited a very dissimilar TL glow curve and behaviour regarding sensitization and fading. Notably, the Norton County aubrite achondrite was found to exhibit a strong fading of the high-temperature peak (~300°C), attributed to anomalous fading, whereas Holbrook did not seem to show signs of anomalous fading. Since quantitative conclusions regarding the thermal and irradiation history of meteorites, require knowledge of the detailed peak structure of the glow curve and deeper understanding of the trapping mechanism, the glow curves, after irradiation in the range 10-2000Gy, were deconvoluted using general order kinetics. The fitting parameters extracted point towards complex non-strictly first order mechanisms with a multitude of traps acting very differently. All the above, combined with future OSL measurements, currently in progress, are expected to shed light on the nature of the involved traps in both phenomena (energy depth, light-resistance etc), which would allow to extract more concrete conclusions about their history.

Component resolved bleaching study in natural calcium fluoride using CW-OSL, LM-OSL and residual TL glow curves after bleaching.

Natural calcium fluoride has been commonly used as thermoluminescence (TL) dosimeter due to its high luminescence intensity. The aim of this work includes attempting a correlation between specific TL glow curves after bleaching and components of linearly modulated optically stimulated luminescence (LM-OSL) as well as continuous wave OSL (CW-OSL). A component resolved analysis was applied to both integrated intensity of the RTL glow curves and all OSL decay curves, by using a Computerized Glow-Curve De-convolution (CGCD) procedure. All CW-OSL and LM-OSL components are correlated to the decay components of the integrated RTL signal, apart from two RTL components which cannot be directly correlated with either LM-OSL or CW-OSL component. The unique, stringent criterion for this correlation deals with the value of the decay constant λ of each bleaching component. There is only one, unique bleaching component present in all three luminescence entities which were the subject of the present study, indicating that each TL trap yields at least three different bleaching components; different TL traps can indicate bleaching components with similar values. According to the data of the present work each RTL bleaching component receives electrons from at least two peaks. The results of the present study strongly suggest that the traps that contribute to TL and OSL are the same.

Preliminary thermoluminescence investigation of commercial pharmaceutical glass containers towards the sterilization dosimetry of liquid drugs.

Drug sterilization with ionizing radiation is a well-established technology, which is constantly extending to several products due to its numerous advantages, since it allows the heat-free sterilization of heat-sensitive pharmaceutical preparations. In a previous study, the possibility to identify irradiated solid-state drugs by means of OSL and TL was examined with very promising findings. In the same respect, the present work aims, for the first time to the authors' best knowledge, to explore whether TL can be employed as a method for post-sterilization dosimetry on commercial liquid-state drugs, by studying the properties of their glass containers. Two different types of glass containers (bottle and ampoule) of two widely used liquid drugs, i.e., Hexalen® and Voltaren®, are used for this purpose. Both glass containers exhibit a linear TL dose response for doses up to 6kGy with a stable behavior through time, while no significant sensitization of the main peaks is observed. Thus, preliminary findings are very promising towards the post-sterilization dosimetry of liquid drugs and the use of the containers of commercial liquid drugs for normal and/or accidental dosimetry.

A cleaning method to minimize contaminant luminescence signal of empty sample carriers using off-the-shelf chemical agents.

Signals acquired during thermoluminescence or optically stimulated luminescence measurements must be completely free of any spurious and/or contamination signals to assure the credibility of the results, especially during exploratory research investigating the luminescence behavior of new materials. Experiments indicate that such unwanted signals may also stem from new (unused) and used empty sample carriers, namely cups and discs, which are widely used for such measurements, probably due to contamination from a fluorite and/or silica-related source. Fluorite and/or silicone oil appear to be the most likely sources of contamination, thus, their removal, along with any other possible source that exhibits undesirable luminescence behavior, is necessary. Conventional cleaning methods fail to eliminate such contaminants from empty cups and discs. In this work a new cleaning method is proposed incorporating off-the-shelf chemical agents. Results of thermoluminescence measurements highlight the efficiency of the new cleaning process, since it can completely remove any observed contaminants from both new and used sample carriers, of various shapes and/or materials. Consequently their signal is minimized even at relatively high beta-doses, where it is prominent, resulting in a clean and only sample-attributed signal.

Preliminary thermoluminescence and optically stimulated luminescence investigation of commercial pharmaceutical preparations towards the drug sterilization dosimetry.

Drug sterilization with ionizing radiation is a well-established technology and is gaining ground the last decades due to its numerous advantages. Identification of irradiated drugs would be interesting and, in this respect, the present work aims, for the first time to the authors' best knowledge, to explore whether OSL and TL can be employed as methods for post-sterilization dosimetry on commercial drugs, i.e., as tools for the detection of irradiated drugs. Five widely used drugs, i.e., Daktarin(®), Aspirin(®), Panadol(®), Brufen(®) and Procef(®), are used for this purpose. Preliminary findings are very promising towards the post-sterilization dosimetry and the use of commercial drugs for normal and/or accidental dosimetry.