Retrospective and emergency dosimetry in response to radiological incidents and nuclear mass-casualty events: A review

This paper reviews recent research on the application of the physical dosimetry techniques of electron paramagnetic resonance (EPR) and luminescence (optically stimulated luminescence, OSL, and thermoluminescence, TL) to determine radiation dose following catastrophic, large-scale radiological events. Such data are used in dose reconstruction to obtain estimates of dose due to the exposure to external sources of radiation, primarily gamma radiation, by individual members of the public and by populations. The EPR and luminescence techniques have been applied to a wide range of radiological studies, including nuclear bomb detonation (e.g., Hiroshima and Nagasaki), nuclear power plant accidents (e.g., Chernobyl), radioactive pollution (e.g., Mayak plutonium facility), and in the future could include terrorist events involving the dispersal of radioactive materials. In this review we examine the application of these techniques in ‘emergency’ and ‘retrospective’ modes of operation that are conducted on two distinct timescales. For emergency dosimetry immediate action to evaluate dose to individuals following radiation exposure is required to assess deterministic biological effects and to enable rapid medical triage. Retrospective dosimetry, on the other hand, contributes to the reconstruction of doses to populations and individuals following external exposure, and contributes to the long-term study of stochastic processes and the consequential epidemiological effects. Although internal exposure, via ingestion of radionuclides for example, can be a potentially significant contributor to dose, this review is confined to those dose components arising from exposure to external radiation, which in most studies is gamma radiation.The nascent emergency dosimetry measurement techniques aim to perform direct dose evaluations for individuals who, as members of the public, are most unlikely to be carrying a dosimeter issued for radiation monitoring purposes in the event of a radiation incident. Hence attention has focused on biological or physical materials they may have in their possession that could be used as surrogate dosimeters. For EPR measurements, in particular, this includes material within the body (such as bone or tooth biopsy) requiring invasive procedures, but also materials collected non-invasively (such as clippings taken from finger- or toenails) and artefacts within their personal belongings (such as electronic devices of which smart phones are the most common). For luminescence measurements, attention has also focused on components within electronic devices, including smartphones, and a wide range of other personal belongings such as paper and other polymer-based materials (including currency, clothing, bank cards, etc.). The paper reviews progress made using both EPR and luminescence techniques, along with their current limitations.For the longer-established approach of retrospective dosimetry, luminescence has been the most extensively applied method and, by employing minerals found in construction materials, it consequently is employed in dosimetry using structures within the environment. Recent developments in its application to large-scale radiation releases are discussed, including the atomic bomb detonations at Hiroshima and Nagasaki, fallout from the Chernobyl reactor and atmospheric nuclear bomb tests within the Semipalatinsk Nuclear Test Site and fluvially transported pollution within the Techa River basin due to releases from the Mayak facility. The developments made in applying OSL and TL techniques are discussed in the context of these applications. EPR measurements with teeth have also provided benchmark values to test the dosimetry models used for Chernobyl liquidators (clean-up workers), residents of Semipalatinsk Nuclear Tests Sites and inhabitants of the Techa River basin.For both emergency and retrospective dosimetry applications, computational techniques employing radiation transport simulations based on Monte Carlo code form an essential component in the application of dose determinations by EPR and OSL to dose reconstruction problems. We include in the review examples where the translation from the physical quantity of cumulative dose determined in the sampled medium to a dose quantity that can be applied in the reconstruction of dose to individuals and/or populations; these take into account the source terms, release patterns and the movements of people in the affected areas. One role for retrospective luminescence dosimetry has been to provide benchmark dose determinations for testing the models employed in dose reconstruction for exposed populations, notably at Hiroshima and Nagasaki. The discussion is framed within the context of the well-known radiation incidents mentioned above.     

TL/OSL properties of crystalline inclusions from heavy,barytes loaded,concrete

In the present work, we report the luminescence data obtained from heavy, barytes loaded, concrete containing many crystalline inclusions, extracted from a shielding block located at CERN. The use of both Thermoluminescence (TL) and Optically Stimulated Luminescence (OSL) signals, resulting from a specific trap at about 200 °C, is investigated for retrospective dosimetry purposes. By applying thermal cleaning experiments the TL signal of interest was isolated. Basic TL and OSL properties as thermal and optical stability, repeatability and mainly the linearity of the TL and OSL signals as a function of beta dose were investigated. The implications of all these luminescence properties to retrospective dosimetry are also briefly discussed.     

Luminescence techniques: instrumentation and methods

This paper describes techniques, instruments and methods used in luminescence dating and environmental dosimetry in many laboratories around the world. These techniques are based on two phenomena – thermally stimulated luminescence and optically stimulated luminescence. The most commonly used luminescence stimulation and detection techniques are reviewed and information is given on recent developments in instrument design and on the state of the art in luminescence measurements and analysis.     

Using the OSL single-aliquot regenerative-dose protocol with quartz extracted from building materials in retrospective dosimetry

We report on the application of the single-aliquot regenerative-dose (SAR) protocol to the optically stimulated luminescence signal from quartz extracted from fired bricks and unfired mortar in retrospective dosimetry. The samples came from a radioactive materials storage facility, with ambient dose rates of about 0.1 mGy/h. A detailed dose-depth profile was analysed from one brick, and compared with dose records from area TL dosemeters. Small-aliquot dose-distributions were analysed from the mortar samples; one associated with the exposed brick, and one from a remote site exposed only to background radiation. We conclude that unfired materials have considerable potential in retrospective dosimetry.     

Luminescence properties of common glasses for application to retrospective dosimetry

Seventeen domestic and scientific glass specimens were investigated for thermoluminescence (TL) properties suitable for application to retrospective population dosimetry. Usefulness for retrospective dosimetry was initially judged by the presence of well-defined TL glow peaks and the absence of irradiation-independent luminescence. Of particular interest were TL glow peaks having relatively low trap depths, to prevent significant natural dose accumulation. Minimum useful trap lifetimes would be in the order of weeks. Surveys were undertaken to observe the TL and optically stimulated luminescence (OSL) behaviour of each sample. Most samples showed identifiable TL, with Pyrex in particular, and samples from a jar, a lampshade, and opaque blue beads all showing well-defined TL glow peaks with sensitivities that were not significantly affected by prior irradiation and heating of the sample. Kinetic analysis of these samples showed that their TL emission originates from traps with suitable stability for retrospective dosimetry. It is concluded that, while some glass samples show promising results, the inherent variability of an amorphous substance such as glass means that the suitability of each sample must be determined on a case-by-case basis.     

Advantages and disadvantages of luminescence dosimetry

Owing to their excellent dosimetric properties, luminescence detectors of ionizing radiation are now extensively applied in individual dosimetry services. The most frequently used personal dosemeters are based on Optically Stimulated Luminescence (OSL), radiophotoluminescence (RPL) or thermoluminescence (TL). Luminescence detectors have also found several applications in clinical dosimetry, especially around new radiation modalities in radiotherapy, such as Intensity Modulated Radiotherapy (IMRT) or ion beam radiotherapy. Requirements of luminescence detectors applied in individual and clinical dosimetry and some recent developments in luminescence of detectors and techniques leading to significant improvements of the functionality and accuracy of dosimetry systems are reviewed and discussed.     

An international perspective on radiological threats and the need for retrospective biological dosimetry of acute radiation overexposures

The widespread use of ionizing radiation sources (machine-generated or from the decay of radioactive materials) across many disciplines including medicine, industry, and academia, has led to hundreds of instances in which one or more persons received an acute radiation overexposure. Successful medical diagnosis and management of these victims rested in part on a rapid, accurate determination of absorbed dose, which in many cases must be retrospective, due to the paucity of useful dosimetry data. This has led to the development of a number of biological dosimetry techniques to determine absorb dose retrospectively. The frequency of these accidental overexposures, however, has failed to serve as the impetus for the development of a cadre of experts in this field and an expansion in the number and availability of centers to perform the more sophisticated analysis necessary to accurately determine absorbed dose. Meanwhile, the world has seen an increase in the number of lethal terrorist events with time and there is realistic concern that the perpetrators of these events strongly desire to employ the specter of acute radiation overexposure in the future to induce mass panic in their target population. To that end, if any of these organizations achieves success, the existing capacity for rapid, accurate retrospective determination of absorbed dose may be overwhelmed, resulting in sub-optimal outcomes for the victims of such an event and potential mismanagement of medical resources designated for their care. This paper reviews existing techniques for retrospective biological dosimetry and diagnosis in relation to past experiences with overexposures, explores potential malevolent overexposure scenarios, and examines the need for public authorities to enhance national capabilities in light of the growing risk of an incident that will result in multiple acute radiation overexposures.     

Retrospective dosimetry using Japanese brick quartz: A way forward despite an unstable fast decaying OSL signal

Quartz extracted from heated bricks has been previously suggested for use in dose estimation in accident dosimetry, but this technique has never been applied before to Japanese quartz which often has unusual OSL characteristics. In this study the optically stimulated luminescence (OSL) characteristics of quartz extracted from a Japanese commercial red brick produced by Mishima – Renga – Seizoujyo Co. are studied. These companies are based in the Aichi Prefecture (capital Nagoya), which accounts for about half of the red brick production in Japan. A comparison of TL (thermoluminescence) and OSL signals has been carried out towards identification of common source traps. It is observed that OSL from Japanese brick quartz shows unusual luminescence characteristics; in particular, the initial fast decaying OSL signal contains a dominant (>90%) thermally unstable component related to the 85 °C TL peak, which necessitates a prior heat treatment. A single-aliquot regenerative-dose (SAR) protocol is developed and tested using thermal treatments intended to isolate a stable dosimetric signal. A minimum detection limit of ～65 mGy is then estimated using this protocol. Following irradiation using ⁶⁰Co and ¹³⁷Cs, dose–depth profiles were measured on two different commercial brick types (Mishima – Renga – Seizoujyo Co. and Hase – Renga Co.) with 5 Gy and 10 Gy surface doses. The profiles derived from the two sources were readily distinguishable. It is concluded that the OSL signals from the two types of Japanese brick quartz examined here can be used to derive precise estimates of accident dose, and, possibly to distinguish between sources of gamma radiation in a nuclear accident.To our knowledge, this is the first report on the existence of an unstable fast decaying OSL signal in quartz derived from bricks, and demonstrates a way forward with such samples in retrospective dosimetry.     

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.     

Study of TSL and OSL properties of dental ceramics for accidental dosimetry applications

Interest is increasing in the development of new methodologies for accidental dose assessment, exploiting the luminescence and dosimetric properties of objects and materials which can be usually found directly on exposed subjects and/or in the contaminated area.In this work, several types of ceramics employed for dental prosthetics restoration, including both innovative materials used as sub-frames for the construction of the inner part of dental crowns (core), and conventional porcelains used for the fabrication of the external layer (veneer), were investigated with regard to their thermally and optically stimulated luminescence (TSL and OSL respectively) properties, in view of their potential application in accidental dosimetry.The sensitivity to ionizing radiation proved to strongly depend on the type and brand of ceramic, with minimum detectable dose ranging from few mGy up to several tens of mGy. A linear dose–response was observed for most of the samples. However, the luminescence signals were characterised by a significant fading, which has to be taken into account for a reliable accidental dose assessment after a radiation exposure event.     

EPR spectroscopy of radiation-induced centers in tooth enamel and its application for retrospective dosimetry in chernobyl case

A specific EPR tooth enamel dosimetry is discussed which appears to have genuine utility in retrospective dosimetry. The sample preparation technology, digital form of the native background and radiation-induced signals, and their separation from the experimentally observed spectrum are discussed. The possibility of dose estimation from the single initial EPR spectrum of randomly irradiated teeth and the uncertainty of such evaluation are discussed. The method has been used for dose reconstruction of a group of people irradiated due to the Chernobyl accident, and some results are presented.     

Insect wings as retrospective/accidental/forensic dosimeters: An optically stimulated luminescence investigation

Estimation of the radiation released during nuclear accidents or radiological terrorist events is imperative for the prediction of health effects following such an exposure. In addition, in several cases there is a need to identify the prior presence of radioactive materials at buildings or sites (nuclear forensics). To this direction, several materials have been the research object of numerous studies the last decade in an attempt to identify potentially new retrospective/accidental/forensic dosimeters.However, the studies targeting biological materials are limited and their majority is mainly focused on the luminescence behavior of human biological material. Consequently, the use of such materials in retrospective dosimetry presumes the exposure of humans in the radiation field. The present work constitutes the first attempt to seek non-human biological materials, which can be found in nature in abundance or in/on other living organisms. To this end, the present work investigates the basic optically stimulated luminescence behavior of insect wings, which exhibit several advantages compared to other materials. Insects are ubiquitous, have a short life expectancy and exhibit a low decomposition rate after their death.Findings of the present study are encouraging towards the potential use of insects' wings at retrospective/accidental/forensic dosimetry, since they exhibit linear OSL response over a wide dose range and imperceptible loss of signal several days after their irradiation when they are kept in dark. On the other hand, the calculated lower detection limit is not low enough to allow their use as emergency dosimeters when individuals are exposed to non-lethal doses. In addition, wings exhibit strong optical fading when they are exposed to daylight and thus special care should be taken during the sampling procedure in order to use the wings as accidental/forensic dosimeters, by seeking (dead) insects in dark places, such as behind furniture, equipment or in air-shafts.Finally, a new single aliquot measurement protocol is also successfully tested on the wings for the dose estimation, while further work is in progress to validate it on other (heat-sensitive) materials as well.     

Dose rate measurements with a ruby-based fiber optic radioluminescent probe

Fiber optic radioluminescence dosimetry allows real-time dose rate measurements in complex, narrow geometries and at places of high dose rates, without exposing the operator or the susceptible electronics. The keys are the spatial separation of radiation sensitive probe and electronic processing system and their optical connection by a flexible light guide. The small probes are capable of measuring fields of high dose rate gradients and the sealed probe-tip qualifies for applications in the fluid milieu and even for in-vivo-dosimetry. One problem of fiber optic dosimetry is the generation of Cherenkov radiation and fiber luminescence in the irradiated light guide, the so called stem effect. Ruby (Al₂O₃:Cr) has a narrow radioluminescent emission at 694 nm and is a potential luminophor for fiber optic radioluminescence dosimetry. In this work the influence of the stem effect on our ruby-based fiber optic dosimetry system is examined. The behavior of ruby probes under irradiation up to 0.5 kGy, as well as their luminescence decay characteristics and the applicability for measurements in radiotherapeutic fields are investigated.     

Luminescence studies on rγ-ray-irradiated Dy3+-activated sodium chloride phosphor for radiation dosimetry

The lyoluminescence (LL), thermoluminescence and mechanoluminescence (ML) of a γ -ray-irradiated powder of NaCl:Dy (0.05–0.5 mol%) phosphor are reported in this paper. The nature of intensity variation of the respective luminescence spectra with different γ -ray doses and with different concentrations of Dy³⁺ doped in NaCl are found to be similar. The LL and ML intensities differed from each other, but their nature is found to be similar in a sublinear form up to a high dose (5.0 kGy) of γ -rays. Thus, the prepared phosphor may be useful for accidental radiation dosimetry up to a high dose (5.0 kGy) of γ -rays using the LL and ML techniques.     

On the use of OSL of chip card modules with molding for retrospective and accident dosimetry

The potential of optically stimulated luminescence of wire-bond chip card modules with molded encapsulations for retrospective and accident dosimetry is investigated. Contact-based and contactless modules were studied, the latter finding potential use in electronic documents (e.g. electronic passports, electronic identity cards). Investigations were carried out on intact as well as chemically prepared modules, extracting the filler material. Contact-based modules are characterized according to zero dose signal, correlation between OSL and TL, dose response and long-term signal stability. For prepared modules, the minimum detectable dose immediately after irradiation is 3 mGy and between 20 and 200 mGy for contact-based and contactless modules, respectively. Dose recovery tests on contact-based modules indicate that the developed methodology yields results with sufficient accuracy for measurements promptly after irradiation, whereas a systematic underestimation is observed for longer delay times. The reasons for this behaviour are as yet not fully understood.     

Limits of retrospective accident dosimetry by EPR and TL with natural materials

The radiation response of natural materials and domestic articles was investigated by EPR and TL to select suitable materials for retrospective dose assessment in accident dosimetry. The thermal stability and the influence of UV-exposure to the radiation-induced EPR centres were investigated. Based on a required precision of ±20% for dosimetry the lower limits of applicability of the materials were determined. The lowest dosimetry limits of 0.5 Gy were found using sugar, boiler scale and egg shells by EPR and 0.3 Gy by using TL with boiler scale. A list of materials found not to be applicable for retrospective radiation accident EPR dosimetry is also given.     

Luminescence properties of α-Al2O3 dosimetric crystals exposed to a high-current electron beam

The spectra of pulsed cathodoluminescence (PCL) and thermoluminescence (TL) in TLD-500 detectors, which were exposed to a strong beam from a pulsed electron accelerator, have been studied. Additional bands in the PCL spectrum and new peaks in the TL curves, which are due to impurity ions, have been revealed. Luminescence bands of F- and F⁺-centers cannot be used in the dosimetry of strong electron beams using TLD-500 detectors because of the saturation of dose dependence and the decrease in the TL yield. It is shown that high doses from these beams can be measured by recording TL in the luminescence band of impurity titanium ions.     

Using optically stimulated electrons from quartz for the estimation of natural doses

A flow-through Geiger-Müller pancake electron detector attachment has been fitted to a standard Risø TL/OSL reader enabling optically stimulated electrons (OSE) to be measured simultaneously with optically stimulated luminescence (OSL). Using this detector, OSE and OSL measurements from natural quartz samples are studied to examine the possible use of OSE as a chronometer. First the relative variability in OSE and OSL growth curve shapes and the effect of preheat on these are presented, and from these curves, conclusions are drawn concerning the charge movement in natural quartz. Secondly, a dose recovery test shows that OSE can successfully recover a laboratory dose of 300 Gy given before any laboratory thermal treatment, for preheating temperatures between 160 and 260 °C. Furthermore, for the first time natural OSE decay curves are detected and these signals are used to estimate a burial dose using the single-aliquot regenerative-dose (SAR) procedure. Finally, a comparative study of the equivalent doses estimated using both OSE and OSL from 10 quartz samples are presented, and it is shown that OSE has a significant potential in retrospective dosimetry.     

Biological Dosimetry by the Triage Dicentric Chromosome Assay - Further validation of International Networking

Biological dosimetry is an essential tool for estimating radiation doses received to personnel when physical dosimetry is not available or inadequate. The current preferred biodosimetry method is based on the measurement of radiation-specific dicentric chromosomes in exposed individuals' peripheral blood lymphocytes. However, this method is labour-, time- and expertise-demanding. Consequently, for mass casualty applications, strategies have been developed to increase its throughput. One such strategy is to develop validated cytogenetic biodosimetry laboratory networks, both national and international. In a previous study, the dicentric chromosome assay (DCA) was validated in our cytogenetic biodosimetry network involving five geographically dispersed laboratories. A complementary strategy to further enhance the throughput of the DCA among inter-laboratory networks is to use a triage DCA where dose assessments are made by truncating the labour-demanding and time-consuming metaphase-spread analysis to 20 to 50 metaphase spreads instead of routine 500 to 1000 metaphase spread analysis. Our laboratory network also validated this triage DCA, however, these dose estimates were made using calibration curves generated in each laboratory from the blood samples irradiated in a single laboratory. In an emergency situation, dose estimates made using pre-existing calibration curves which may vary according to radiation type and dose rate and therefore influence the assessed dose. Here, we analyze the effect of using a pre-existing calibration curve on assessed dose among our network laboratories. The dose estimates were made by analyzing 1000 metaphase spreads as well as triage quality scoring and compared to actual physical doses applied to the samples for validation. The dose estimates in the laboratory partners were in good agreement with the applied physical doses and determined to be adequate for guidance in the treatment of acute radiation syndrome.     

Electron paramagnetic resonance radiation dosimetry in fingernails

There is now an increased need for accident dosimetry due to the increased risk of significant exposure to ionizing radiation from terrorism or accidents. In such scenarios, dose measurements should be made in individuals rapidly and with sufficient accuracy to enable effective triage. Electron paramagnetic resonance (EPR) is a physical method of high potential for meeting this need, providing direct measurements of the radiation-induced radicals, which are unambiguous signatures of exposure to ionizing radiation. For individual retrospective dosimetry, EPR in tooth enamel is a proven and effective technique when isolated teeth can be obtained. There are some promising developments that may make these measurements feasible without the need to remove the teeth, but their field applicability remains to be demonstrated. However, currently it is difficult under emergency conditions to obtain tooth enamel in sufficient amounts for accurate dose measurements. Since fingernails are much easier to sample, they can be used in potentially exposed populations to determine if they were exposed to life-threatening radiation doses. Unfortunately, only a few studies have been carried out on EPR radiation-induced signals in fingernails, and, while there are some promising aspects, the reported results were generally inconclusive. In this present paper, we report the results of a systematic investigation of the potential use of fingernails as retrospective radiation dosimeters.