Materials for thermoluminescent dosimetry: Current status and future trends

Studies and applications of thermoluminescence (TL) dosimetric materials are reviewed. It is shown that the properties of commercial TL dosimeters satisfy a set of stringent requirements. The search and development of storage materials with required TL properties is based on approaches that involve the evaluation of the luminescence light yield. The specific features required for the dosimetry of high-energy particles and fast and thermal neutrons are considered. The use of TL with deep traps in high-temperature dosimetry is discussed. Results of pioneering studies of TL in nanosized materials are briefly presented.     

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.     

Ultraviolet dosimetry using thermoluminescent phosphors-rate dependence

Intrinsic thermoluminescence response of various TL phosphors to ultraviolet radiation is found to be highly exposure rate dependent. The explanation lies in the nature of exciton assisted process in TL materials. TL phosphors should be employed for UV dosimetry with due caution.     

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.     

Semi-automatic scanning of tracks in plastics

Some irradiated saccharides emit light when dissolved in water. Glucose, xylose and mannose were selected as the most suitable materials for lyoluminescence dosimetry. Using ⁶⁰Co as a radiation γ-source, the performance of these materials has been evaluated from the point of view of sensitivity, stability against thermal annealing or exposure to light and their linear behaviour with doses up to 100 krads. Their lower limit, depending upon the apparatus used is about 100 rads. With trehalose 2H₂O and luminol solution, doses between 1 and 10⁶ were measured.

It appears that trapped free radicals are responsible for the light emission. An attempt has been made to correlate their esr spectra with their lyoluminescent behaviour. But the actual mechanism of light emission needs further investigation.     

Response of a track-etch-based LET-spectrometer to high-energy protons

The spectrometer of linear energy transfer (LET) was developed. It is based on the chemically etched polyallyldiglycolcarbonate (PADC) track-etch detector. LET spectra are estimated through track parameter determination and analysed by an automatic optical image analyser LUCIA G. Three PADC materials were used: 0.5 mm thick Page, 0.5 and 1 mm thick Tastrak; they were exposed to protons with energies up to 1000 MeV. Such energetic protons are generally not directly registrable in any of PADCs mentioned; the tracks observed correspond mostly to secondary particles created through nuclear interactions of primary protons. LET spectra permit to calculate the dose absorbed in the detector due to these secondary particles and to compare it with the ionization collision dose of primary protons. It is observed that the dose due to secondary particles represents a few percent of the ionization collision dose. Their ratio varies slightly with proton energy, and some differences between the three PADCs used were also observed. The importance of results obtained for on-board spacecraft dosimetry is analysed and discussed.     

An application of artificial neural intelligence for personal dose assessment using a multi-area OSL dosimetry system

Significant advances have been made in recent years to improve measurement technology and performance of phosphor materials in the fields of optically stimulated luminescence (OSL) dosimetry. Pulsed and continuous wave OSL studies recently carried out on alpha-Al2O3:C have shown that the material seems to be the most promising for routine application of OSL for dosimetric purposes. The main objective of the study is to propose a new personal dosimetry system using alpha-Al2O3:C by taking advantage of its optical properties and energy dependencies. In the process of the study, a new dose assessment algorithm was developed using artificial neural networks in hopes of achieving a higher degree of accuracy and precision in personal OSL dosimetry system. The original hypothesis of this work is that the spectral information of X- and gamma-ray fields may be obtained by the analysis of the response of a multi-element system. In this study, a feedforward neural network using the error back-propagation method with Bayesian optimization was applied for the response unfolding procedure. The validation of the proposed algorithm was investigated by unfolding the 10 measured responses of alpha-Al2O3:C for arbitrarily mixed photon fields which range from 20 to 662 keV.     

Dosimertry characteristics and performance comparisons: Environmental radiophotoluminescent glass dosemeters versus thermoluminescent dosemeters

This paper describes the dosimetry characteristic comparison of environmental radiophotoluminescent glass dosemeter (RPLGD) and thermoluminescent dosemeter (TLD) systems employed at the Institute of Nuclear Energy Research (INER, Taiwan). The luminescence centers of TLD disappeared by reading process, and repetition of measurement is impossible. RPLGDs can be repeatedly read and keep the luminescence centers for a long time. The RPLGD fading is about 1% within 30 days after being exposed to ionizing radiation. Environmental cumulative doses measured by a RPLGD and a TLD were compared at the same monitoring points of INER during two years. The sensitivity of TLD decreased with gradual loss due to fading at higher temperatures. The difference between results obtained by RPLGD and TLD is discussed mainly with respect to the dependence on the ambient temperature. In addition, this research also refers to the American National Standard Institute (ANSI) Draft Standard N13.29 (1996) to organize the environmental dosimetry performance tests of the INER's RPLGDs and the TLDs. The results mean that both kinds of dosemeters can meet the performance test criteria. An accreditation procedure for the institutes which provide the environmental dosimetry services in Taiwan was suggested based on the comparison results of these two dosimetry systems.     

Characterization of the gafchromic EBT3 films for dose distribution measurements in stereotactic radiotherapy

Radiochromic film dosimetry is a promising technique, but at this time there are some artefacts, including non-uniformity, energy dependence and scanner artefacts. Accurate dosimetry with radiochromic films requires characterizing the film as well as the scanning and analysis procedures. In this work, the performance of the EBT3 films in combination with the EPSON Dual Lens Perfection V700 scanner for dose distribution measurements in stereotactic radiotherapy has been evaluated. It has been shown that it was necessary to perform 20 blank scans to obtain the stability of the scanner. In order to reduce the uncertainties due to the non-uniformity of the scan field, it was then decided to use the 12 × 12 cm² central part of the scanner bed. Regarding EBT3 films, intra-sheet and inter-sheet uniformity of unexposed EBT3 films in terms of pixel value has been found to be respectively 0.27% (1 SD) and 0.15% (1 SD). No significant energy dependence has been observed above 30 keV and no angular dependence has been found.     

EURADOS intercomparisons for individual monitoring services: Results of the 2012 whole body intercomparison

In 2008, EURADOS (the European Radiation Dosimetry Group) started to organise a self-sustained programme of regular intercomparisons with the aims of encouraging and facilitating the participation of individual monitoring services (IMS) in intercomparisons. To date, three intercomparisons for whole body dosemeters (IC2008, IC2010 and IC2012) and one for extremity dosemeters (IC2009) have been carried out. This paper presents the recent results of the 2012 intercomparison for whole body dosemeters. At the 2012 intercomparisons 75 institutes with 87 dosimetry systems (most passive) participated from 28 European and 2 non-European countries. For the irradiations a number of different reference photon radiation qualities (x-ray and nuclide sources) were used. The results show that 90% of all systems fulfil the general performance criteria from ISO 14146. The paper gives a comprehensive overview on the performance of various European dosimetry services and the influence of the dosemeter type and detector material on the resulting response values.     

Coded waveforms for optimised air-coupled ultrasonic nondestructive evaluation

This paper investigates various types of coded waveforms that could be used for air-coupled ultrasound, using a pulse compression approach to signal processing. These are needed because of the low signal-to-noise ratios that are found in many air-coupled ultrasonic nondestructive evaluation measurements, due to the large acoustic mismatch between air and many solid materials. The various waveforms, including both swept-frequency signals and those with binary modulation, are described, and their performance in the presence of noise is compared. It is shown that the optimum choice of modulation signal depends on the bandwidth available and the type of measurement being made.     

Dosimetric properties of natural quartz grains extracted from fired materials

The paper describes an examination of the dosimetric properties of natural quartz grains extracted from ancient fired materials. Eleven samples of different origin were tested for their TL and GLSL (green light stimulated luminescence) sensitivities within the mGy dose range. Very promising results were obtained showing the possibility of measuring the doses of around 10 mGy with 1% precision using GLSL or TL and using the single aliqout technique for natural quartz as a dosimeter. The lowest detectable dose was estimated to be lower than 500 μGy. The results obtained indicate that natural quartz grains from selected materials could be used for the dosimetry of environmental gamma radiation for the purposes of paleodosimetric dating methods as well as for accident dosimetry.     

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.     

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.     

Non-contact measurement of the electric field shielding performance and the resistivity of layer materials

An approach is described to measure the electric field shielding performance of materials as a function of frequency. This provides a broader appreciation of the performance of materials than is available from standard energy transfer type measurements. Materials that include metallic conducting components show little variation of shielding performance with frequency, whereas the performance of resistive materials falls away with increasing frequency. It is shown that the variation of attenuation with frequency relates to the resistivity on or within the material. This has particular practical relevance to the risk of occurrence of damaging or incendive electrostatic discharges from charged material surfaces.     

A novel dosimetry system for computed tomography using phototransistor

Computed tomography (CT) dosimetry normally uses an ionization chamber 100 mm long to estimate the computed tomography dose index (CTDI), however some reports have already indicated that small devices could replace the long ion chamber to improve quality assurance procedures in CT dosimetry. This paper presents a novel dosimetry system based in a commercial phototransistor evaluated for CT dosimetry. Three detector configurations were developed for this system: with a single, two and four devices. Dose profile measurements were obtained with them and their angular responses were evaluated. The results showed that the novel dosimetry system with the phototransistor could be an alternative for CT dosimetry. It allows to obtain the CT dose profile in details and also to estimate the CTDI in longer length than the 100 mm pencil chamber. The angular response showed that the one device detector configuration is the most adequate among the three configurations analyzed in this study.     

Non-destructive characterization of delaminated areas at interfaces between plies in carbon fiber/epoxy laminates with Foucault currents

Carbon fiber epoxy laminates are extensively used in the aerospace industry as they offer a combination of high performance with relatively low weight. However, damage may occur in these materials, either at the manufacturing level or during use, which may affect their structural integrity. Among the type of damage which may occur, delamination is a common defect which causes a reduction in compressive strength and thus limits the life of laminated composites. If undetected, delamination may propagate during use due to mechanical loads and in the worst case may cause fracture of the material. Therefore, delamination in composite materials needs to be efficiently detected and accurately quantified for safety and economic reasons. Because of their heterogeneity, multi-layered structure and anisotropy, the inspection of composite materials remains difficult with conventional NDT methods. A method making use of Foucault currents, and relying on the principle of electromagnetic induction, can be adapted for the detection and characterization of damage in composite materials. The use of Foucault currents in characterizing delaminated areas at interfaces between plies in carbon fiber/epoxy laminates is addressed in this paper. It is demonstrated that Foucault currents can accurately detect and quantify delamination in CFRP materials. Furthermore, the potential of this technique for monitoring defect propagation in composite materials is discussed.     

Gafchromic® film dosimetry for low energy X radiation

Recent developments have produced low energy X ray systems capable of providing a radiation dose to adequate volumes suitable for sterile inset programmes. To support the adoption of these new systems, the performance of the Gafchromic^® HD-810 dosimetry system previously used for gamma irradiation needed to be better understood at the lower photon energies. For low energy photons, the optical density of the irradiated Gafchromic HD-810 film dosimeters significantly depends on the material surrounding them. For example, if paper, Mylar^® or PVC is used to house the dosimeter during irradiation, the optical density can vary by as much as a factor of three or more for the same dose. This paper is an attempt to elucidate the performance of the Gafchromic HD-810 film dosimeters for such low energy X radiation (∼150 keV). Our data show that this behaviour can be explained by the fact that these materials have significantly different photon mass attenuation coefficient. This conclusion was reinforced with mathematical simulation using Monte Carlo modelling. We also show that with the different structure of another Gafchromic film dosimeter (MD-V2-55) this effect is virtually non-existent. An understanding of the behaviour of thin film dosimeters like Gafchromic HD-810 under radiation is crucial for reliable dosimetry. We hope that this work can also provide guidance in the use of other thin film dosimeters at similar low photon energies.     

Electron spin resonance (ESR) dating and ESR applications in quaternary science and archaeometry

The scope of application of ESR spectroscopy has greatly expanded with the advent of its widespread use in radiation exposure dating around 1980 and its use in retrospective dosimetry since the Chernobyl disaster in 1986. Few fields of study are of such breadth that they span topics as diverse as dating of human origins, volcanic activity, cave deposits and earthquakes, while also providing prognoses for radiation accident victims. Between 1945 and 1975 ESR was mainly used to define the nature of paramagnetic defects in crystalline and amorphous materials, which laid the foundation for its use in applied areas in Quaternary geology, archaeometry and accident dosimetry. This review chronicles the development of the use of ESR in applied science since 1975, with particular emphasis on the state of the art in the period 1987–1997. The first part of the review focuses mainly on the range of applications for datable materials: tooth enamel (Section 2), calcite (Section 3) and quartz (Sections 4–9), while the second part comprises the areas of retrospective dosimetry (Section 10) and new applications (Section 11). The review concludes (Appendix A) with an introduction to the physical basis and assumptions involved in ESR dating, and compilations of valuable reference works for students and workers in this field.     

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.