Computerized Curve Deconvolution Analysis Research Articles

Detection of baby food sterilized with ionizing radiation using thermoluminescence

AbstractFood sterilization with ionizing radiation is a well-established technology, which is constantly extending to several products due to its numerous advantages. However, radiosterilization is prohibited to several food categories, such as baby food products since it could cause nutrient degradation of such foods with significant effects on the infants’ health. As a result, any governmental agency responsible for the detection of irradiated products should first focus on products consumed by babies/children. To this respect, the present work explores whether TL can be employed as a method for post-sterilization dosimetry on baby food, by studying the properties of their glass containers since they would be equally and jointly exposed to the ionizing radiation during the sterilization process. Two different reputable brands, i.e., Hipp® and Nestle®, are used for this purpose. Both glass containers exhibit a linear TL dose response for doses up to 3 kGy, while no sensitization of the main peaks is observed. Though their behavior is not very stable with time (strong fading) yet fading correction is possible. Dose recovery tests were successfully conducted, calculating the administered dose with high accuracy. A computerized curve deconvolution analysis (CCDA) was also performed revealing that all glow curves can be fitted with one peak of continuous trap distribution and three discrete-energy peaks, which also demonstrate a linear dose response over the range 50–3000 Gy. Thus, findings are very promising towards the post-sterilization dosimetry of baby food through their glass containers.

Thermoluminescence characterization and kinetic parameters of eyeglass lenses for applications in retrospective/accidental dosimetry

Many researchers study the luminescence properties of objects consisting of glass, aiming to applications for retrospective/accidental dosimetry. In this context, eyeglass lenses are used globally and be worn by large portion of the population. In a case of an accident with radiation release, they can be recovered to assess the exposure dose of the general population in the vicinity of the accident.The scope of the present study is to conduct, for the first time, a detailed study of the thermoluminescence properties of eyeglass lenses along with computerized curve deconvolution analysis which would shed light on the kinetics involved to explore their suitability as dosimeters. The dose range under study is between 0.1 and 16 Gy.Results, which appear independent of the chemical composition of the lenses, indicate that the glow curves of the eyeglass lenses have overlapping peaks, while an inherent signal (zero-dose) may also appear, probably produced during the manufacturing process. The materials do not exhibit sensitization effects, and they present linear dose response for doses up to 16 Gy. A dose recovery test predicts with high accuracy an “unknown” delivered dose. The remaining signal after one-month post-irradiation is sufficient for conducting post-radiation measurements.A computerized curve deconvolution analysis (CCDA) indicates the co-existence of at least two discrete-energy traps and one continuous-distribution trap. After the TL deconvolution of the glow curves, for all doses and all eyeglass lenses, the kinetic parameters were determined for all the components.A preliminary study is also conducted towards the elimination of the unwanted inherent signal. Hydrofluoric acid presents the most promising treatment method, among two chemical methods that were applied in the present work.The results of the current study enhance the potential use of the eyeglass lenses as dosimetric probes in the case of an accident that involves radiation release and exposure of the general population.

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 characterization of minerals extracted from dried oregano for retrospective and/or sterilization dosimetry

Silicate minerals extracted by dried herbs are broadly used for the determination of food products that are sterilized by means of radiation. At the same time, it is necessary to calculate the applied sterilization dose for these products, since there are certain pre-defined dose limits for the variant food categories.In addition, researchers seek for materials that can be used in retrospective/accidental dosimetry, in the cases that there is no available data from personal dosimeters. In this perspective, dried oregano is used worldwide and is a popular herb for most households.The purpose of this study is twofold; the evaluation of the extracted minerals for the assessment of the post-sterilization dose and the estimation of the accidental dose that certain population might have been exposed to. In order to succeed this purpose, a thorough characterization of the thermoluminescence (TL) properties of the silicate minerals was conducted. Two dose ranges were studied, for the two different applications mentioned above, namely a range between 0.050 and 4 kGy and a range between 1 and 20 Gy. ResultsData reveal that the glow curve of the silicate minerals has at least three overlapping peaks in the dosimetric spectrum. The material exhibits strong sensitization effects, which can be suppressed by including a sensitization correction within the applied protocols. All three peaks demonstrate linear dose response for doses up to 20 Gy, while for the range of 0.050 Gy–4 kGy a saturation curve is used for the fitting.An unknown delivered dose is successfully estimated by a dose recovery test, when the applied dose belongs to the lower dose range. The stability of the signal with respect to the storage time differs for the three peaks and the remaining signal is appreciable for 1 month post irradiation.Finally, a Computerized Curve Deconvolution Analysis (CCDA) was conducted, based on the equations of the general order kinetics. The TL glow curves of all doses were successfully deconvoluted using eight discrete-energy curves and the corresponding kinetic parameters were also calculated.The findings of the present study support the potential use of the silicate minerals, extracted by dried oregano for accidental/retrospective dosimetric applications.

Use of commercial pharmaceutical drug (Daktarin®) for retrospective/accidental/forensic thermoluminescence dosimetry

Retrospective/accidental dosimetry seeks for materials that can be used as probes for the dose assessment by means of several methods when there is no dose data available (e.g. from personal dosimeters). In the same respect, researchers also seek materials appropriate for forensic purposes, which would allow to identify the prior presence of radioactive materials at buildings, sites or even vehicles.To this direction, several solid-state drugs, which are ubiquitous, have also been studied as probes for the dose estimation in emergency situations. However, due to their heat-sensitive character, measurements were possible only with OSL. The scope of the present work is to identify a heat-resistant drug (Daktarin) and conduct, for the first time, a detailed study of the thermoluminescence properties of it along with computerized curve deconvolution analysis which would shed light on the traps involved.Results indicate that the glow curve of Daktarin has at least three peaks that can be used for dosimetric purposes, since they exhibit linear dose response for doses up to 20 Gy, do not exhibit any sensitization, have high lifetime and their stability with time is good, since an appreciable signal remains unaffected even 3 months post irradiation. All the above were validated conducting dose recovery tests and successfully calculating the unknown delivered dose for various periods after the irradiation of the samples. The new findings are very supportive and point towards the efficient use of commercial pharmaceuticals as probes for retrospective/accidental/forensic dosimetry using thermoluminescence.

Post-sterilization radiation dosimetry of commercial pharmaceuticals using optically stimulated luminescence

Sterilization with gamma irradiation has been established as an acceptable method highly advantageous compared to other methods for the sterilization of several products, including pharmaceutical preparations. However, the effects of irradiated drugs on the consumer when they are introduced in the human body are still unknown. Thus, consumers should be aware if a drug has been irradiated and freely choose whether to consume it or not. Consequently, development of drug irradiation detection methods, useful for regulatory compliance purposes, is an active area of investigation.To this respect, new OSL measurements on five commercial solid drugs (Daktarin®, Aspirin®, Panadol®, Brufen® and Procef®) for radiation doses up to several kGy were conducted in order to investigate if the OSL method can identify irradiated drugs. Dose response study, computerized curve deconvolution analysis (CCDA), fading test and sterilization dose recovery test with the SARHS protocol were conducted to investigate the optically stimulated luminescence (OSL) characteristics of the drugs and the properties of the involved traps.Results indicate that all drugs have a linear dose range up to 1–2 kGy, while the entire dose range can perfectly be fitted with an exponential decay curve. Although the fading rate varies, an appreciable signal remains unaffected even 6 months post irradiation in all drugs. The CCDA revealed that the kinetics are of second order and that all drugs have a very fast component with a lifetime of approximately 0.3–5.6 s. The single aliquot regenerative protocol for the calculation of the equivalent dose in heat-sensitive materials exhibiting sensitization (SARHS), developed in a previous work, was also tested on the solid drugs. The SARHS, which can correct for the sensitization effect without involving any heating, but introducing an optical bleaching procedure between the repeated irradiation/stimulation cycles during the construction of the calibration curve, proved capable of calculating the sterilization dose of irradiated drugs.The new findings are very promising towards the post-sterilization dosimetry of solid drugs, rendering the OSL and the SARHS protocol capable of the detection and the determination of the radiation dose applied in irradiated drugs, after the fading factor has been estimated.

Thermoluminescence properties of CaO powder obtained from chicken eggshells

Eggshell wastage has created serious problem in disposal of the food processing industry which has been triggered the thoughts of researchers to use wasted eggshells as good source of calcium. In the present work, calcium oxide (CaO) has been synthesized by combustion process in furnace (F–CaO) and microwave oven (M–CaO) using the source of chicken eggshells. The obtained F–CaO and M–CaO are characterized by XRD, SEM with EDX and thermoluminescence (TL) technique. XRD pattern of both the samples show cubic phase with crystallite size 45–52nm. TL glow curves are recorded for various gamma radiation dose (300–4000Gy). Two TL glows, a small peak at 424K and stronger peak at 597K are observed. TL response of M–CaO is 2.67 times higher than F–CaO sample. TL kinetic parameters are calculated by computerized curve deconvolution analysis (CCDA) and discussed.

TL and OSL studies of carbon doped magnesium aluminate (MgAl2O4:C)

The MgAl2O4:C has been synthesized by using two different methods by electron gun and vacuum assisted melting of MgAl2O4 in presence of graphite. The MgAl2O4:C phosphor thus developed by these two different methods have similar types of the TL/OSL defects with multiple overlapping TL glow peaks from 100°C to 400°C. The Computerized Curve De-convolution Analysis (CCDA) has been used to measure TL parameters such as thermal trap depth, frequency factor and order of kinetic associated with charge transfer process in TL phenomenon. The investigated TL/OSL results show that these two methods of incorporating carbon in MgAl2O4 have generated closely resemble the defects of similar types in MgAl2O4:C lattice. However, the MgAl2O4:C synthesized by electron gun shows relatively larger concentration of the TL/OSL defects as compared to MgAl2O4:C synthesized using vacuum assisted melting method. The photo-ionization cross-section (PIC) associated with fastest OSL component of MgAl2O4: C is found to be ∼ 0.5 times than that of fastest OSL component of commercially available dosimetric grade α-Al2O3:C. The MgAl2O4:C thus developed shows good dynamic OSL dose linearity from few mGy to 1Gy. This work reveals that MgAl2O4:C could be developed as potential tissue equivalent OSL / TL material.

Radiation dose response correlation between thermoluminescence and optically stimulated luminescence in quartz

The fast, linearly modulated optically stimulated luminescence (LM-OSL) component in quartz is the main dosimetric signal used for the dating applications of this material. Since the blue light stimulation (470nm, 40mWcm −2) time needed to obtain the fast LM-OSL component is less than 50s the electron trapping levels responsible for it are still highly populated. In this way an active radiation history is created which could play an important role in the dosimetric characteristics of the fast OSL signal. In the present work the dose response behavior of the fast OSL signal is investigated in quartz samples with an annealed radiation history and quartz samples possessing an artificial radiation history. A computerized curve de-convolution analysis of the LM-OSL curves for 50s stimulation time showed that it consists of three individual OSL components. The faster component C1 with peak maximum time around 5s has a linear dose response in virgin samples, which turns to a slight superlinearity as a function of the artificial radiation history. On the other hand the component C2 with peak maximum time at 12s is slightly superlinear which turns into strong superlinearity as a function of artificial radiation history. Finally, component C3 with peak maximum time at about 45s is strongly superlinear for both virgin samples and as a function of artificial radiation history. The implications to practical application are discussed.

Computerized curve deconvolution analysis for LM-OSL

The computerized curve deconvolution analysis (CCDA) technique is well known in the case of thermoluminescence (TL). In the present work we investigate the application of CCDA to the linear modulated optically stimulated luminescence curves (LM-OSL). We derive single LM-OSL peak equations which are based on variables which can be extracted directly from the experimental OSL curve, for both first order and general order LM-OSL peaks. The similarities and differences between TL and OSL CCDA analysis are discussed. The resolution of the technique is also examined in the cases of synthetic curves consisting of two or four constituent components. Finally a new experimental procedure is suggested which can be used to separate composite LM-OSL curves into their constituent components