DEVELOPMENTS IN THE USE OF THERMOLUMINESCENCE AND OPTICALLY STIMULATED LUMINESCENCE FROM MOBILE PHONES IN EMERGENCY DOSIMETRY.

Proposed physical dosimetry methods for emergency dosimetry in radiological, mass-casualty incidents include both thermoluminescence (TL) and optically stimulated luminescence (OSL). Potential materials that could feasibly be used for TL and OSL dosimetry include clothing, shoes and personal accessories. However, the most popular target of study has been personal electronics, especially different components from smartphones. Smartphones have been a focus because they are widely available and, in principle, may be viewed as surrogates for commercial TL or OSL dosimeters. The components of smartphones that have been studied include surface mount devices (such as resistors, capacitors and inductors) and glass materials, including front protective glass, display glass and (with more modern devices) back protective glass. This paper reviews the most recent developments in the use of TL and OSL with these materials and guides the way to future, and urgently needed, research.

AN ADVANCE IN EPR DOSIMETRY WITH NAILS.

Olive oil is proposed as a medium for storage of nails in the time between nail harvesting and electron paramagnetic resonance (EPR) measurements to minimise the decay of the radiation-induced EPR signals (RIS). The behaviours of three main EPR signals, namely, RIS, mechanically induced and the background signals (MIS and BG, respectively), were studied for storage in olive oil. The properties of the MIS and BG signals were very similar to those previously observed for the storage in a vacuum. The RIS singlet slightly increased during the first day of storage and then remained practically unchanged at least for 6 days. Dose recovery test revealed that doses at the level 2 Gy may be reconstructed with an accuracy of about ±20%.

A COMPARATIVE STUDY OF EPR AND TL SIGNALS IN GORILLA® GLASS.

Electron Paramagnetic Resonance (EPR) and Thermoluminescence (TL) signals have been studied in samples of Gorilla® Glass (GG) from different smartphones as well as some online stores and vendors. Background, radiation-induced and ultraviolet-induced signals were compared between the samples. Significant variability of both EPR and TL signals (in shape and intensity) was observed between samples from different screens as well as over the surface of the same screen, from the same phone. Both the EPR and TL background signals appear to be due to UV exposure during phone manufacture; some phones have higher EPR and TL signals around the edge of the screen, indicating more UV exposure at the edge than in the center. EPR and TL signals in the same GG samples appear correlated: they decayed over the same temperature region; and both hole- and electron-related EPR and TL signals were made up of stable and unstable components (at room temperature).

A COMPARISON OF DIFFERENT SPECTRA DECONVOLUTION METHODS USED IN EPR DOSIMETRY WITH GORILLA® GLASSES.

Two different spectra deconvolution methods have been compared on samples of Gorilla® Glass (GG) irradiated in the dose range 0-20 Gy and measured with X-band EPR. The first method used a matrix deconvolution procedure using sample-specific sets of reference signals. The second method used a 'universal' set of eight reference signals (due to five electron centers, two hole centers and a background) to fit EPR spectra from any GG sample. Dose-responses curves were constructed for each individual reference signal. These were then used to test reconstruction of a laboratory-administered dose of 2 Gy. For the matrix method, the values of the reconstructed and nominal doses were within ± 20% after averaging measurements from three aliquots of each sample. For the universal method, the most promising results were obtained with E1, E4 and H1 signals. The fitting failed for one sample, due to dominance of the background signal.

Emergency EPR and OSL dosimetry with table vitamins and minerals.

Several table vitamins, minerals and L-lysine amino acid have been preliminarily tested as potential emergency dosemeters using electron paramagnetic resonance (EPR) and optically stimulated luminescence (OSL) techniques. Radiation-induced EPR signals were detected in samples of vitamin B2 and L-lysine while samples of multivitamins of different brands as well as mineral Mg demonstrated prominent OSL signals after exposure to ionizing radiation doses. Basic dosimetric properties of the radiation-sensitive substances were studied, namely dose response, fading of the EPR or OSL signals and values of minimum measurable doses (MMDs). For EPR-sensitive samples, the EPR signal is converted into units of dose using a linear dose response and correcting for fading using the measured fading dependence. For OSL-sensitive materials, a multi-aliquot, enhanced-temperature protocol was developed to avoid the problem of sample sensitization and to minimize the influence of signal fading. The sample dose in this case is also evaluated using the dose response and fading curves. MMDs of the EPR-sensitive samples were below 2 Gy while those of the OSL-sensitive materials were below 500 mGy as long as the samples are analyzed within 1 week after exposure.

Emergency EPR dosimetry technique using vacuum-stored dry nails.

Human finger- and toenails have been tested with an X-band EPR technique for different conditions of nail storage. The main radiation-induced signal at g=2.005 demonstrated good stability if the samples were stored in a vacuum at room temperature after nail harvesting and irradiation. On the basis of this phenomenon, a new protocol is proposed to use the nails as possible emergency EPR dosimeters. The dosimetry protocol was tested on laboratory-exposed samples and demonstrated the ability to recover doses in the region 0-10 Gy with an estimated uncertainty of approximately 0.3-0.4 Gy for doses in the range < 2 Gy, increasing to 0.6-0.7 Gy for doses in the range 5-10 Gy.

INTEGRATED CIRCUITS FROM MOBILE PHONES AS POSSIBLE EMERGENCY OSL/TL DOSIMETERS.

In this article, optically stimulated luminescence (OSL) data are presented from integrated circuits (ICs) extracted from mobile phones. The purpose is to evaluate the potential of using OSL from components in personal electronic devices such as smart phones as a means of emergency dosimetry in the event of a large-scale radiological incident. ICs were extracted from five different makes and models of mobile phone. Sample preparation procedures are described, and OSL from the IC samples following irradiation using a (90)Sr/(90)Y source is presented. Repeatability, sensitivity, dose responses, minimum measureable doses, stability and fading data were examined and are described. A protocol for measuring absorbed dose is presented, and it was concluded that OSL from these components is a viable method for assessing dose in the days following a radiological incident.

Emergency Dose Estimation Using Optically Stimulated Luminescence from Human Tooth Enamel.

Human teeth were studied for potential use as emergency Optically Stimulated Luminescence (OSL) dosimeters. By using multiple-teeth samples in combination with a custom-built sensitive OSL reader, (60)Co-equivalent doses below 0.64 Gy were measured immediately after exposure with the lowest value being 27 mGy for the most sensitive sample. The variability of OSL sensitivity, from individual to individual using multiple-teeth samples, was determined to be 53%. X-ray and beta exposure were found to produce OSL curves with the same shape that differed from those due to ultraviolet (UV) exposure; as a result, correlation was observed between OSL signals after X-ray and beta exposure and was absent if compared to OSL signals after UV exposure. Fading of the OSL signal was "typical" for most teeth with just a few of incisors showing atypical behavior. Typical fading dependences were described by a bi-exponential decay function with "fast" (decay time around of 12 min) and "slow" (decay time about 14 h) components. OSL detection limits, based on the techniques developed to-date, were found to be satisfactory from the point-of-view of medical triage requirements if conducted within 24 hours of the exposure.

Optically stimulated luminescence (OSL) of tooth enamel and its potential use in post-radiation exposure triage.

Optically stimulated luminescence (OSL) properties of dental enamel are discussed with a view to the development of an in vivo dose assessment technique for medical triage following a radiological/nuclear accident or terrorist event. In the OSL technique, past radiation exposure is assessed by stimulating the sample with light of one wavelength and monitoring the luminescence at another wavelength, under the assumption that the luminescence originates from the recombination of radiation-induced charges trapped at metastable defects in the enamel and that the intensity of the luminescence signal is in proportion to the absorbed radiation dose. Several primary findings emerged from this research: (a) sensitivities varied considerably between different teeth and also between fragments of the same tooth, (b) OSL signals were found to decay rapidly during the first 12 h after irradiation and more slowly afterward, (c) the fading rate of the luminescence signal varied between fragments, and (d) blue light stimulation yields greater sensitivity than infra-red stimulation, while the OSL signal obtained with a high-intensity pulsed green-light laser was found not to be correlated with the radiation dose. Significant challenges remain to developing a practical in vivo technique, including the development of calibration procedures and lowering minimum detectable doses.

Optically stimulated luminescence (OSL) dosimetry in medicine.

This paper reviews fundamental and practical aspects of optically stimulated luminescence (OSL) dosimetry pertaining to applications in medicine, having particularly in mind new researchers and medical physicists interested in gaining familiarity with the field. A basic phenomenological model for OSL is presented and the key processes affecting the outcome of an OSL measurement are discussed. Practical aspects discussed include stimulation modalities (continuous-wave OSL, pulsed OSL and linear modulation OSL), basic experimental setup, available OSL readers, optical fiber systems and basic properties of available OSL dosimeters. Finally, results from the recent literature on applications of OSL in radiotherapy, radiodiagnostics and heavy charged particle dosimetry are discussed in light of the theoretical and practical framework presented in this review. Open questions and future challenges in OSL dosimetry are highlighted as a guide to the research needed to further advance the field.

Optically Stimulated Luminescence (OSL) of dental enamel for retrospective assessment of radiation exposure.

This paper briefly reviews the optically stimulated luminescence (OSL) properties of dental enamel and discusses the potential and challenges of OSL for filling the technology gap in biodosimetry required for medical triage following a radiological/nuclear accident or terrorist event. The OSL technique uses light to stimulate a radiation-induced luminescence signal from materials previously exposed to ionizing radiation. This luminescence originates from radiation-induced defects in insulating crystals and is proportional to the absorbed dose of ionizing radiation. In our research conducted to date, we focused on fundamental investigations of the OSL properties of dental enamel using extracted teeth and tabletop OSL readers. The objective was to obtain information to support the development of the necessary instrumentation for retrospective dosimetry using dental enamel in laboratory, or for in situ and non-invasive accident dosimetry using dental enamel in emergency triage. An OSL signal from human dental enamel was detected using blue, green, or IR stimulation. Blue/green stimulation associated with UV emission detection seems to be the most appropriate combination in the sense that there is no signal from un-irradiated samples and the shape of the OSL decay is clear. Improvements in the minimum detection level were achieved by incorporating an ellipsoidal mirror in the OSL system to maximize light collection. Other possibilities to improve the sensitivity and research steps necessary to establish the feasibility of the technique for retrospective assessment of radiation exposure are also discussed.

Low temperature radioluminescence of LiF:Mg,Cu,P.

Low temperature radioluminescence spectra of LiF, variously co-doped with Mg, Cu and P, show highly unusual temperature dependencies which resemble thermoluminescence data. The signals include intense peaks and a relatively weak continuous background. One peak occurs below 30 K, together with a major peak near 125 K. The signals are highly sensitive to the dopants and slightly sensitive to X-ray dose rate. The role of donor acceptor pairs and the perturbations from intrinsic defects formed by ionisation can be used to describe all the observations. The 290 nm emission band is linked to H center annealing.

A system to irradiate and measure luminescence at low temperatures.

We have developed a system to irradiate samples and record radioluminescence (RL), optically stimulated luminescence (OSL), and thermoluminescence (TL) at temperatures ranging from -150 degrees C to 200 degrees C. The system consists of a cryostat, an irradiation/stimulation unit fitted with an X-ray tube (40 kV Moxtek) and a quartz window for optical stimulation, and a detection unit that utilises a photomultiplier tube and an interchangeable filter pack. Experiments have been conducted with quartz and albite (a feldspar). TL and OSL experiments show that several optically sensitive trapping states are stable below -50 degrees C. In addition, an increase in OSL is seen as the OSL stimulation temperature is lowered below -50 degrees C, and an increase in RL is apparent as the temperature is lowered during irradiation. This indicates that not only are optically sensitive low temperature traps present but that luminescence becomes more efficient at low temperatures.

In situ long-term monitoring system for radioactive contaminants.

A long-term in situ subsurface instrument for monitoring radioactive contaminant plumes, as an alternative to soil analysis, is described. A portable, laser-based reader optically stimulates luminescence from sensors, each containing an Al2O3:C dosemeter. The sensors, designed for placement at various subsurface locations around a waste site, are allowed to accumulate dose for a predetermined time that is based on the instrument's minimum detectable dose (MDD). The reader is then attached to the sensor by fibre optic cable to read the accumulated dose; an increase above natural background levels indicating the presence of leaked radioactivity. Based on an MDD of 5 microGy, it is shown that the sensor can measure soil concentrations of 1.85 Bq cm(-3) after an exposure time of 50 h for 137Cs and 67 h for 90Sr/90Y. Discrimination between beta and gamma radiation is possible using an end cap placed over one of the two paired sensors, allowing simultaneous measurement of 137Cs and 90Sr/90Y in a mixed field. The monitor system represents a substantial improvement over quarterly soil sampling because of a greatly increased measurement frequency and the ability to perform measurements reproducibly.

A real-time, high-resolution optical fibre dosemeter based on optically stimulated luminescence (OSL) of KBr:Eu, for potential use during the radiotherapy of cancer.

A real-time optically stimulated luminescence (OSL) dosimetry system for potential in vivo use during radiotherapy treatments is proposed. Single-crystal europium-doped KBr samples were grown in a Bridgman furnace, and characterised using optical absorption techniques. An algorithm for the processing of the OSL signal was defined for use in real-time measurements, and its performance was studied on data obtained with a home-built reader, using optical-fibre-coupled dosemeters. OSL dose-response, fading properties and temperature dependence of the signal were investigated in correlation with the concentration of Eu(2+) dopant in the sample.

The use of optically stimulated luminescence from AL2O3:C in the dosimetry of high-energy heavy charged particle fields.

This paper presents two different approaches of quantifying the optically stimulated luminescence (OSL) response of Al(2)O(3):C to high-energy heavy charged particles (HCPs). The OSL efficiency of Al(2)O(3):C exposed to different HCPs is defined as the sensitivity of the material to HCPs normalised by the sensitivity to gamma. In this paper, we investigate the possibility of introducing a 'mean efficiency' eta(mean), which when used in conjunction with the total gamma dose D(gamma) measured for a mixed radiation exposure allows for the determination of the absorbed dose without the need to determine the individual contributions of different types of radiation to the OSL signal. We tested the hypothesis that information regarding the 'mean efficiency' eta(mean) is contained in the shape of the OSL decay curve, using several approaches in the analysis of the OSL data. This analysis was applied to various mixed field irradiations performed at the HIMAC facility, Chiba, Japan. The results of this analysis are discussed.

Experimental determination of the dose deposition profile of a 90Sr beta source.

Three different methods for characterising the dose deposition profile of a (90)Sr/(90)Y radioactive source are described: GAFChromic film dosimetry, Thermoluminescence (TL) and Optically Stimulated Luminescence (OSL). For the film measurements, GAFChromic film samples were stacked at different depths between polyethylene terephthalate (PET) foils. For TL, the thickness of a TLD-500 dosemeter was gradually reduced by polishing and the TL from chips of different thickness was used in conjunction with a mathematical model based on the exponential attenuation of dose inside the crystal to determine the decay constant for the dose-depth profile. Finally, an OSL reader with confocal stimulation / detection capabilities was used to map the two-dimensional dose distribution in TLD-500 dosemeters as a function of depth. The shapes of the dose deposition profiles obtained from all the investigated methods are in good agreement.

Radiation dosimetry for microbial experiments in the International Space Station using different etched track and luminescent detectors.

The laboratory of Microbiology at SCK.CEN, in collaboration with different universities, participates in several ESA programmes with bacterial experiments that are carried out in the International Space Station (ISS). The main objective of these programmes is to study the effects of space flight conditions such as microgravity and cosmic radiation on the general behaviour of model bacteria. To measure the radiation doses received by the bacteria, different detectors accompanied the microbiological experiments. The results obtained during two space flight missions are discussed. This dosimetry experiment was a collaboration between different institutes so that the doses could be estimated by different techniques. For measurement of the high linear energy transfer (LET) doses (>10 keV microm(-1)), two types of etched track detectors were used. The low LET part of the spectrum was measured by three types of thermoluminescent detectors ((7)LiF:Mg,Ti; (7)LiF:Mg,Cu,P; Al(2)O(3):C) and by the optically stimulated luminescence technique using Al(2)O(3):C detectors.

Progress towards a polymineral single-aliquot OSL dating procedure.

Published single-aliquot regenerative-dose (SAR) procedures for quartz use a 'cutheat' different from the pre-heat. In contrast, previous work has shown that the SAR procedure can be used to correct for sensitivity changes exhibited by feldspars if the cutheat is equal to the pre-heat. In this paper, a procedure that corrects for sensitivity changes in both quartz and feldspar is tested. The results indicate that for sedimentary quartz the cutheat can be equal to the pre-heat. Thus, it may be possible to develop one procedure to measure equivalent doses in a polymineral sample. We also tested several different optical stimulation methods. Using the infrared (IR)-stimulated signal from a post-IR blue-stimulated optically stimulated luminescence sequence extends the potential age range when using feldpathic materials. In addition, since the post-IR blue-stimulated signal from feldspar is much smaller than the blue-stimulated signal from quartz, the possibility exists of extracting a 'quartz signal' from a mixed mineral sample.

Near-real-time radiotherapy dosimetry using optically stimulated luminescence of Al2O3:C: mathematical models and preliminary results.

In this paper we report investigations aimed toward applying optically stimulated luminescence (OSL) of Al2O3:C for near-real-time medical dosimetry, especially in radiotherapy. The classical mathematical model normally used for the description of OSL phenomena was expanded to predict the behavior of the luminescence signal in the case when the OSL sample is simultaneously irradiated and optically stimulated. The predictions obtained were used to develop different measurement approaches and correction algorithms for the luminescence signals, thus enabling dose estimation from OSL during rather then after the irradiation procedure. Radiation probes with diameters of less than 1 mm, suitable for the envisioned in-vivo measurements were constructed by attaching small Al2O3:C crystals to optical fiber cables. The OSL fiber probes and a purpose-built, portable OSL stimulation and readout system were used to measure doses at speeds up to 1 data point every 3s, under irradiation at dose rates of the same order of magnitude as those found in conventional radiotherapy techniques. The corrected OSL signal was found to be proportional to the absorbed dose, and accurately followed sudden transitions in the irradiation dose rate.