Optically Stimulated Luminescence Signal Research Articles

The variability of single grain quartz luminescence properties investigated using EMCCD imaging

Optically stimulated luminescence (OSL) signals from individual quartz grains are frequently used for equivalent dose and age determination in luminescence dating. Typically, signals from individual grains are stimulated with a focussed solid-state laser and detected via a photomultiplier tube. In contrast to the light-emitting diodes (LEDs) usually used when stimulating multiple-grain aliquots, the laser has a much higher stimulation power density. An absolute value for the effective stimulation power cannot easily be quantified, and the power delivered to each grain cannot be considered consistent throughout a measurement sequence. Both intra- and inter-sample variability in single grain luminescence signals parameters such as dose response form, decay rate, and sensitivity have long been recognised, however there remains uncertainty over how much of this variability is intrinsic to quartz grains or whether some should be attributed to variation in the effective stimulation power associated with the laser system. To better characterise intrinsic variability of single quartz OSL signals, an electron multiplier charge coupled device (EMCCD) attachment for the Risø reader was used for detecting and imaging luminescence signals. Whilst the EMCCD system currently offers a lower detection sensitivity when compared to the laser system, the ability to use LEDs for stimulation of the OSL signal circumvents the power variability associated with the laser system and allows an investigation of intrinsic variability to be made. In this paper, signal intensity and the composition of components in single grain luminescence signals are considered, and curve deconvolution is undertaken to calculate photo ionisation cross-sections for single grain quartz signals. For the samples considered, intra-sample variability in these characteristics is observed in single grain quartz luminescence signals imaged using an EMCCD.

A preliminary study of the radioluminescence and optically stimulated luminescence of CaF2:Ce,Dy phosphor

The aim of this work was to study the radioluminescence (RL) and optically stimulated luminescence (OSL) properties of CaF2:Ce,Dy. For this purpose, samples of CaF2:0.4 mol% Ce,0.4 mol% Dy in pellet form were used. Experimental results have shown that the inclusion of Ce and Dy in this phosphor provides a good OSL sensitivity in a wide dose range from 0.022 up to 126 Gy. Besides, a minimum detectable dose of 0.01 Gy and an OSL fading of approximately 30% after 20 h of storage in darkness were found. Finally, the RL and OSL signals of CaF2:Ce,Dy are compared with those of the commercial TLD-200 (CaF2:Dy) dosimeter.

Luminescence characterization of Ce and Gd doped MgB4O7 phosphors

This paper presents the results of the structural and luminescence characterization of Ce3+ and Gd3+ doped MgB4O7 powders produced by the solid-state synthesis technique. The phase composition of the samples was confirmed by X-ray Diffraction (XRD) method. Morphological characterization using a Scanning Electron Microscope (SEM) revealed a regular surface morphology with spherical/cylindrical grains. The luminescent properties were examined by measuring the RL emission spectra, Optically Stimulated Luminescence (OSL) decay signal, and Thermoluminescence (TL) glow curve. The correlation between luminescence intensity and concentration quenching of the prepared phosphor was investigated. The results show a maximum luminescence efficiency when the synthesis of MgB4O7:Ce,Gd was carried out using contents of 0.1 wt% Ce3+ and 3 wt% Gd3+. The data shows that at the heating rate of 5 °C/s, MgB4O7:Ce0.1%,Gd3% exhibits five TL peaks: two rapidly decaying peaks at about 80 °C and 110 °C, a shoulder peak at 180 °C, a high sensitivity peak at 235 °C TL and another shoulder peak at 320 °C (temperatures are approximate). The step annealing patterns suggest that the origin of the OSL signal is associated with the TL traps located between 180 and 235 °C. The kinetic parameters using various heating rate (VHR) technique, Tm-Tstop assisted extended initial rise method (IRM) and computerized glow curve deconvolution (CGCD) method were obtained and compared. The phosphor showed the dose linearity up to 10 Gy beta dose with a slight supralinearity for higher doses and the minimum detectable dose value of 743.1 ± 11 μGy. Fading and reusability studies of MgB4O7:Ce0.1%,Gd3% further confirmed the phosphor suitability for radiation dosimetry.

The build-up of the laboratory-generated dose-response curve and underestimation of equivalent dose for quartz OSL in the high dose region: A critical modelling study

The application of a regeneration procedure for optically stimulated luminescence (OSL) dating requires that the dose-response curve (DRC) of a natural sample is the same as that of a laboratory-generated one. However, the build-up of the laboratory-generated DRCs of quartz has been widely reported in the literature, i.e., the laboratory-generated DRCs are significantly higher than the natural counterparts in the high dose region (above 150 or 200 Gy). This results in severe underestimation of equivalent dose (D e ) for quartz OSL in the high dose region during the application of a single-aliquot regenerative-dose (SAR) protocol. However, the potential mechanism governing the build-up of the laboratory-generated DRC is still unclear. In this study, we performed a comprehensive investigation of the natural and laboratory-generated OSL signals and DRCs using a kinetic model for quartz. We compared the differences in charge concentrations between natural and laboratory-irradiated aliquots following irradiation and monitored the competition for holes and electrons during preheat and stimulation, for the natural, regenerative, and test dose cycles. In the course of the modelling, we could see the build-up of laboratory-generated DRCs, the underestimation of D e , and a double exponential saturation characteristic of the DRCs. We demonstrated a discrepancy in competition for electrons in the deep electron trap and recombination centres during stimulation between the natural, regenerative, and test dose cycles. The simulation results are directly relevant to quartz OSL D e determination using the SAR protocol and reveal the mechanisms responsible for the experimentally observed different behaviours between natural and laboratory-generated DRCs.

Standardized Dose–Response Curve (sDRC) Construction for OSL Dating of Quartz from Bohai Coast, NE China

The optically stimulated luminescence (OSL) dating method promises to provide reliable ages for various Quaternary archives. Coastal sedimentation in the Bohai Sea (northeastern China) since the Middle Pleistocene has been influenced by paleoenvironmental and sea-level change, of which dating has been restricted using the OSL dating approach in multiple investigations. In this study, to establish a robust OSL chronological framework of the Bohai coastal sediments more effectively, the regional standardized dose–response curve (sDRC) was constructed for quartz OSL dating in the Bohai Coast (NE China) using two existing approaches. The sDRC-determined equivalent doses are broadly in agreement with those using the individual DRC for each sample. Data used for DRC construction of the fine-grained (FG) quartz samples are less scattered than those of the coarse-grained (CG) quartz samples, probably due to the signal-averaging effect for the FG samples, while the OSL signal of the CG quartz samples might document provenance information that yield relatively scattered distribution. The two approaches used in this study yield identical sDRCs, indicating that both the methods are applicable for sDRC construction in the Bohai Sea.

Optically stimulated luminescence dating using quartz

Optically stimulated luminescence (OSL) signals from quartz can be used to determine when sedimentary archives were deposited. OSL dating uses the accumulation of energy stored in a crystal structure to measure time. This stored energy is absorbed from ionizing radiation, and is released (reset) by heat or daylight. The total specific energy (dose) absorbed since the last resetting is measured using OSL, and divided by the rate of storage (dose rate) to give the time elapsed from the last heating or daylight exposure. In this Primer, quartz OSL dating is introduced and the signal resetting processes outlined. We describe the origins and quantification of the dose rate and the daylight-sensitive OSL signal most appropriate to dose estimation. The most widely used dose measurement method is then discussed, together with quality-control procedures. A broad set of geological and archaeological studies are used to illustrate the wide range of potential applications, and we describe the challenges arising from different deposition environments and summarize evidence for the precision and accuracy of published ages. Uncertainties and minimum reporting are discussed together with methodological limitations, particularly when applied to young and old sediments. Finally, we highlight the anticipated future developments in the field.

Retrospective physical dosimetry in the Czech Republic: an overview of already established methods and recent research

Purpose The threat of serious radiation exposures to members of the public from radiological incidents and nuclear events has led to intensive study of a number of emergency dosimetry techniques for purposes of triage. As such, a national laboratory of retrospective dosimetry was established in our institute. The purpose of this work is to provide a summary of the well-established and already implemented retrospective physical dosimetry techniques based on thermoluminescence (TL), optically stimulated luminescence (OSL) and neutron activation including their specifics. Moreover, we present some new results of the experimental work, in which we compared dosimetry potential of various dental repair materials and human teeth. Materials and methods At first, an overview of already established retrospective physical retrospective methods including their main features was compiled. As regards recent research, an experimental comparative study was performed under defined conditions. The materials used were aliquots prepared from both pure and repaired teeth and aliquots of unused dental ceramics of known type. Following irradiation, we compared TL and OSL curves of the materials. We also compared dosimetry characteristics of OSL signal as reproducibility, dose dependence and fading. Results After irradiation, the teeth aliquots of dental enamel and dentin exhibited very low OSL and TL signals compared with aliquots containing some dental repair materials or aliquots of pure dental ceramics. With a few exceptions, the OSL signal of dental enamel and dentin aliquots irradiated to 2 Gy was hardly distinguishable from OSL signal corresponding to unirradiated aliquots. In contrast, aliquots of teeth containing some dental repair material and aliquots of pure dental ceramics provided a well reproducible OSL signal exhibiting linear dose response. All the materials tested exhibited a significant fading of the OSL signal. The loss of OSL signal during the first 24 hours after irradiation was from 20 to 99% of its original value obtained immediately after the irradiation. Conclusions The already established physical methods of retrospective dosimetry use a spectrum of verified materials and techniques for dose assessment in the aftermath of serious radiological incidents and nuclear events. In the comparative study, we found that the dosimetry potential of teeth in natural state is much worse compared to teeth repaired with dental ceramics or dental cement fillings. Teeth restored with dental repair materials exhibited relatively favorable dosimetry characteristics. However, they can be usable for a dose reconstruction only on condition that the main practical problems connected with fading and optical bleaching were solved.

3D Dosimetry Based on LiMgPO4 OSL Silicone Foils: Facilitating the Verification of Eye-Ball Cancer Proton Radiotherapy.

A direct verification of the three-dimensional (3D) proton clinical treatment plan prepared for tumor in the eyeball, using the Eclipse Ocular Proton Planning system (by Varian Medical Systems), has been presented. To achieve this, a prototype of the innovative two-dimensional (2D) circular silicone foils, made of a polymer with the embedded optically stimulated luminescence (OSL) material in powder form (LiMgPO4), and a self-developed optical imaging system, consisting of an illuminating light source and a high-sensitive CCD camera has been applied. A specially designed lifelike eyeball phantom has been used, constructed from 40 flat sheet LMP-based silicone foils stacked and placed together behind a spherical phantom made by polystyrene, all to reflect the curvature of the real eyeball. Two-dimensional OSL signals were captured and further analyzed from each single silicone foil after irradiation using a dedicated patient collimator and a 58.8 MeV modulated proton beam. The reconstructed 3D proton depth dose distribution matches very well with the clinical treatment plan, allowing for the consideration of the new OSL system for further 3D dosimetry applications within the proton radiotherapy area.

Construction and use of rock-cut cisterns: a chronological OSL approach in the arid Negev Highlands, Israel

The Negev Highlands (Israel) are characterized by a rich settlement history over the last millennia. To sustain life in this arid environment, measures to collect and store water were introduced. Two types of installations to collect and store runoff water were built in the region: open reservoirs, and more elaborate subterranean rock-cut cisterns. This article focuses on the latter. Based on a few inscriptions found in rock-cut cisterns, it is assumed that the majority were constructed in the Hellenistic (Nabatean) to Byzantine period. To evaluate this age assessment, this study was carried out at the Borot Hazaz cisterns system, using optically stimulated luminescence (OSL) dating together with micromorphological analyses. Both were applied to sediments that were relocated during the cistern’s construction and usage and after the maintenance activities ended. Despite unfavourable conditions for resetting the OSL signal, including fluvial transport over short distances and sediment deposition by humans in large quantities, it was possible to reconstruct the life cycle of the cistern system. The present study places the construction of the system during the late Roman to Byzantine period, with utilization and long-term maintenance during the following centuries. Maintenance ceased at the Borot Hazaz cistern system gradually over the course of the last 500 years.

A non-destructive, high-sensitivity, emergency dosimetry method using OSL from protective back-glasses from smartphones

A non-destructive, high-sensitivity, dose-reconstruction method is proposed and tested using optically stimulated luminescence (OSL) from protective back-glasses from modern smartphones. A custom-made OSL reader, capable of accommodating the entire phone, has been built for this purpose and preliminary results are reported. The back-glass is stimulated using several light-emitting diodes (LEDs) while a radiation-induced OSL signal is detected with a high-sensitivity photomultiplier tube. A set of appropriate filters is used for separation of stimulation and emission light. The sensitivity of the system was tested for different wavelengths (colors) of stimulation light. A maximum sensitivity was observed using so-called Royal Blue LEDs, with stimulation centered at a wavelength of 447.5 nm. The following dosimetric properties have been studied: (1) background and radiation-induced OSL curves; (2) dose-response curves for several back-glasses from different phones and the corresponding values of the minimum detectable doses; and (3) fading of the OSL signal with time after irradiation. Background (BG) OSL signals were negligible in all tested phones except one (an iPhone 11), in which the BG signal was equivalent to a dose of ~157 mGy. However, the BG OSL had a different decay-curve shape compared to that of the radiation-induced signal (RIS). This difference in shape allows the two signals to be distinguished and separated. Strong, radiation-induced OSL signals were observed in all glasses after irradiation, but with significant variability in sensitivity among the different phones. The dose-response relationships for all phones were linear in the range 0–2.7 Gy when the OSL signals were measured at the same effective time after irradiation. Values of the minimum detectable doses were in the range 0.2–4.3 mGy for the different phones when measured 3 min after exposure. Fading of the OSL signal was observed for storage times up to 11 days after irradiation and was best-fitted by a power function. Dose recovery tests were carried out on two phones intentionally exposed to a dose of 266 mGy and their OSL measured 6 and 7 days, respectively, after irradiation. During these periods the phones were kept in their original cases but were used as usual for calls, messages, internet surfing, etc. Fading-corrected OSL doses were determined to be 199 mGy and 220 mGy, respectively, which are within 25% of the nominal value.

Luminescence dating of holocene siliciclastic sediments in eastern Dahomey Basin, southwestern Nigeria

Several attempts at reconstructing geological settings and palaeoclimatic changes of the siliciclastic deposits of the Dahomey Basin, SW Nigeria, using relative age dating and correlation methods, have resulted in serious discrepancies on the ages. Therefore, a chronology framework established by an absolute age dating method is requisite to constrain the geological interpretation. This research focuses on quartz optically stimulated luminescence (OSL) dating of the upper siliciclastic sediments to help bridge the lacuna that arose from previous relative geologic dating. Ten sub-surface sediment samples were collected from the eastern part of the basin, and quartz OSL dating using single-aliquot regenerative-dose protocol was conducted for all the samples. The OSL signals appear well bleached prior to deposition and the OSL ages are reliable and robust. Through the application of OSL, the age framework of the uppermost part of sediments in the study area was established. The OSL dating results revealed that these depositional periods fall within the Holocene and are concentrated during two groups: 3.52 ka–1.55 ka, and 0.64 ka–0.05 ka. The samples with ages of 3.52 ka–1.55 ka distribute in the belt-like inland zone approximately parallel to the coastline. This deposition episode appears to be caused by the decrease in relative sea level during late Holocene. Thus, this study sheds light on the understanding past coast dynamics in the region.

Optically stimulated luminescence dosimetry on mobile phone back protective glass

Protective glasses from the back of modern smartphones were tested as potential emergency dosimeters using optically stimulated luminescence (OSL). The glasses were shown to exhibit several favorable dosimetric properties including a strong sensitivity to radiation, a linear dose-response relationship from 0.1 to 8 ​Gy, a 3% reproducibility, and a minimum detectable dose in the low tens of milligray, even after significant fading. The OSL signal was observed to lose ~78% and ~90% of the original intensity over 1 ​h and 1 week, respectively; however, a fading curve was developed to correct for any such signal loss. A dose-recovery test demonstrated that reconstructed doses were capable of accuracies within 20%.

The Oyambre coastal terrace: a detailed sedimentary record of the Last Interglacial Stage in northern Iberia (Cantabrian coast, Spain).

ABSTRACTA detailed study is presented of a 15.3‐m‐thick Pleistocene coastal terrace located on the Cantabrian coast (northern Spain). Stratigraphic, sedimentological, topographic and micropalaeontological information is combined with a chronology based on luminescence dating to characterize the deposits. The sedimentary succession records: (i) a basal transgressive system, consisting of a wave‐cut surface covered by a lower layer of beach gravels and upper beach pebbly sands; and (ii) a thicker upper highstand system (aggrading), comprising medium to very fine aeolian sands interbedded with thin palustrine muds. Luminescence dating involved a detailed sampling strategy (36 samples and two modern analogues) and the use of both quartz optically stimulated luminescence (OSL) and feldspar post‐infrared infrared stimulated luminescence single aliquot regeneration protocols; feldspar results were used to confirm the completeness of bleaching of the quartz OSL signal. The quartz OSL luminescence age–depth relationship shows significant dispersion, but nevertheless two rapid phases of deposition can be clearly identified: one at ~130 ka [Marine Oxygen Isotope Stage (MIS) 5] and one at ~100 ka (MIS 5c). The top of the succession is dated to ~70 ka. The MIS 5e marine maximum flooding surface is identified at an elevation of 6.85 m above mean seal level. This elevation provides evidence of a regional sea‐level highstand for this sector of the Cantabrian coast.

Variation of luminescence sensitivity, characteristic dose and trap parameters of quartz from rocks and sediments

We investigated the optically stimulated luminescence (OSL) and thermoluminescence (TL) characteristics of quartz from sediments and parent rocks across South America. OSL and TL sensitivities were compared with the characteristic dose of dose response curves. Additionally, we estimated electron trap parameters of quartz from sediments with contrasting OSL sensitivities. Our results show that the natural sensitivities of quartz OSL (initial 0.8 s) and TL (110 °C peak) are positively correlated and range over six and four orders of magnitude respectively. The corresponding characteristic doses range from around 30 Gy–3000 Gy for dose response curves described by a single exponential function. Quartz from igneous and metamorphic rocks and Andean short-transported sediments report low-sensitivity OSL and high characteristic dose. The studied initial OSL signal has significant contribution of medium and slow components in quartz from rocks and Andean short-transported sediments, while in quartz from Brazilian long-transported sediments, the initial OSL signal is dominated by the fast component. The trend of sensitivity increase and characteristic dose decrease is attributed to the relative contribution of medium and low components to the initial OSL emission. Regarding the electron trap parameters, high, medium and low sensitivity quartz has statistically similar values of the activation energy and the frequency factor, but both parameters have larger variations in medium and low sensitivity quartz.

Dose response features of quenched and reconstructed, TL and deconvolved OSL signals in BeO

Despite the fact that Beryllium oxide (BeO) has been suggested by several research groups as an alternative passive radiation detector and dosimetric material, various concerns about supralinear dose response features were raised for both thermoluminescence (TL) and optically stimulated luminescence (OSL) signals of this material. This paper presents a detailed dose response study on BeO, for two different experimental conditions, namely for (i) the TL signal following irradiation at room temperature (RT), 125 and 200 °C and (ii) the CW – OSL signal measured at three different measurement temperatures (RT, 100 and 220 °C), following two different preheating temperatures (Tpre = 100 and 220 °C). The selection of these temperatures is based on the TL glow curve structure for BeO. The analysis was performed using (a) the actual experimental luminescence signals which suffer thermal quenching, and (b) by using the reconstructed luminescence signals, after correcting for thermal quenching. Deconvolution was performed only for the OSL signals. Intense supralinearity features for both TL peaks and OSL components are reported. Reconstruction affects greatly the dose response features of all TL signals, enhancing supralinearity. The dose response linearity coefficient μ of the dominant OSL component C1 is found to be independent of the preheating temperature. This provides a strong argument for the fact that the charge associated with this component originates mainly from the trap responsible for the TL peak 3 in BeO with Tm beyond 300 °C. Based on our experimental results, the supralinearity features of BeO are attributed to competition for free electrons by electron traps. The results of the present study suggest that competition takes place during both the irradiation and heating stages of a dose response experiment in BeO. Finally, preheating at 220 °C and subsequent OSL measurement at 100 °C is highly recommended as the optimum configuration for BeO, not only for roughly linear dose response but also in order to minimize transfer effects.

Application of standardised growth curves in quartz OSL dating of lacustrine sediments on the Mongolian Plateau

The standardised growth curves (SGCs) can compensate for the drawbacks of the single-aliquot regenerative-dose (SAR) procedure, such as low utilization of time and instrument in the optically stimulated luminescence (OSL) dating. In this study, 12 sedimentary samples of 6 lakes from the Mongolian Plateau were selected and 90–125 μm coarse-grains quartz was extracted to establish SGCs. The results show that the OSL signals are mainly composed of a fast component, which is applicable for SAR procedure. The difference in the shape of the dose response curves (DRCs) limits the application of the standardised growth curve (SGC) for which the growth curves among the aliquots corrected by the test dose are scattered. The equivalent dose (De) estimated by the global standardised growth curve (gSGC) by the regenerative normalization (re-normalization) method is more consistent with the full SAR procedure, so the gSGC method is suitable for determining the De values on the regional scale of Mongolian Plateau. For different lacustrine sedimentary samples, the De values estimated by full SAR procedure and gSGC method are consistent for the doses of up to ~280 Gy. The discrepancy of growth curves may result from the sensibility changes of inter-cycle in SAR measurement and the recuperation, also we do not exclude the influence of feldspar inclusions.

Use of optically stimulated luminescence (OSL) in the detection of irradiated spices.

In this study, the validity of using the optically stimulated luminescence (OSL) technique as a scanning method for the detection of irradiated foodstuffs was investigated. Gamma-irradiated thyme, mint and clove samples were stimulated with a continuous wave blue light (CW-OSL) and their OSL signal sensitivity and stability properties were measured. While no OSL signal was observed for all non-irradiated spices, a significant increase in the intensity of OSL signals was noted for all samples after irradiation with 5kGy, 10kGy and 20kGy. It was also observed that the measured OSL signals were well above the background level even after one year of irradiation. It is therefore concluded that irradiated thyme, mint and clove samples can clearly be identified using the CW-OSL technique without any pre-treatment even one year after irradiation. This result indicates that, where spices contain sufficient silicate minerals, the CW-OSL technique could be used as a method for detecting irradiation.

Modeling the charge deposition in quartz grains during natural irradiation and its influence on the optically stimulated luminescence signal

The rate of charge deposition in quartz grains irradiated in natural conditions is computed by radiation transport modeling. Quartz luminescence models are modified with the addition of the resulting charge deposition term, and the influence of this process on the optically stimulated luminescence (OSL) signal is analyzed. The results indicate that the charge deposition occurring in the quartz grain during the time of residence within rock could lead to the depletion of trapped holes in the recombination centres. For the two different quartz models investigated here, complete depletion is expected to occur for rock ages between 500 Ma and 1100 Ma. It is predicted that for sedimentary quartz derived from such rocks, the OSL signal is dominated by the slow component. It was also found that the shape and saturation level of the natural sensitivity-corrected dose response curve (DRC) of quartz is affected by the charge deposition; specifically, a linear reduction of the saturation level with the age of the rock is observed.

Modelling the dependence of equivalent dose determined from a dose recovery test on preheating temperature: The intervention of shallow electron traps

In optically stimulated luminescence (OSL) dating, the performance of the single-aliquot regenerative-dose (SAR) protocol is commonly tested using a dose recovery test. The dependence of equivalent dose (De) determined in a dose recovery test on preheating temperature using quartz OSL was reported in previous studies which demonstrated that using a lower preheating temperature prior to the measurement of the test dose OSL response may result in serious underestimation of the recovered De. In this study, we simulate the variation of normalised sensitivity-corrected OSL signals as a function of cycle number and the dependence of the recovered De on preheating conditions, using a kinetic model consisting of four electron traps and two recombination centres. Experimentally observed phenomena are successfully reproduced using the model with a set of optimised kinetic parameters. We suggest that the intervention of shallow electron traps may play a significant role in affecting the accuracy of De determination. Relevant mechanisms are explained, and implications on dose measurements using the SAR protocol are discussed.

OSL with chips from US credit cards

Chips from credit cards issued by the major US banks have been tested with optically stimulated luminescence (OSL) as potential materials for use in emergency radiation dosimetry. The following dosimetric properties have been studied: (1) OSL decay curves from both irradiated and unirradiated samples; (2) dose-response characteristics of the OSL and values of minimum detectable doses; (3) fading of the OSL signal with time after irradiation. No OSL was detected in unexposed samples while prominent signals were observed after irradiation. It was found that the shape of the OSL signals can be fitted by a combination of an exponentially decaying function and a power function. The dose-response relationship was linear in the range 0–7 Gy if the OSL signals were measured at the same effective time after irradiation and normalized to the response to a test dose. Dose recovery tests demonstrated that the doses can be reconstructed with an accuracy ±20% if the OSL measurements are conducted within 7 days after exposure and the corresponding OSL doses are corrected for fading.