EPR tooth dosimetry of SNTS area inhabitants

doi:10.1016/j.radmeas.2007.05.007

Radiation Measurements

Volume 42, Issues 6–7, July–August 2007, Pages 1037-1040

https://doi.org/10.1016/j.radmeas.2007.05.007 Get rights and content

Abstract

The determination of external dose to teeth of inhabitants of settlements near the Semipalatinsk Nuclear Test Site (SNTS) was conducted using the EPR dosimetry technique to assess radiation doses associated with exposure to radioactive fallout from the test site. In this study, tooth doses have been reconstructed for 103 persons with all studied teeth having been formed before the first nuclear test in 1949. Doses above those received from natural background radiation, termed “accident doses”, were found to lie in the range from zero to approximately 2 Gy, with one exception, a dose for one person from Semipalatinsk city was approximately 9 Gy. The variability of reconstructed doses within each of the settlements demonstrated heterogeneity of the deposited fallout as well as variations in lifestyle. The village mean external gamma doses for residents of nine settlements were in the range from a few tens of mGy to approximately 100 mGy.

Introduction

The accuracy of retrospective dosimetry for inhabitants of the Semipalatinsk area remains a topical problem. Estimates of absorbed dose in the same settlements of this region obtained using various techniques (i.e. EPR dosimetry with teeth, luminescence dosimetry with quartz, and analytical dose reconstruction based on measurements of exposure rate or ¹³⁷Cs ground deposition) may vary several fold (Bailiff et al., 2004, Ivannikov et al., 2006, Stepanenko et al., 2006b). Furthermore, even for the same technique (e.g. model-based dose reconstruction), the estimated doses within a settlement may differ significantly (Stepanenko et al., 2006a). The village of Dolon is a good example, where reported estimates from different techniques cover the range from 0.1 to 2 Gy. This large range highlights the need for additional measurements with high-precision dosimetric techniques and subsequent improvement to the calibration aspects of the calculation techniques.

EPR dosimetry with tooth enamel is known as one of the most accurate and reliable dosimetric techniques (Chumak et al., 1999, IAEA, 2002). Its distinct advantage is that the accident doses are derived from physical measurements of human tissues. This is especially important for a non-uniformly contaminated area, e.g. the various villages around the SNTS, where fallout clouds from individual nuclear tests varied considerably in their directions of travel and the amount of fallout deposited (Gordeev et al., 2006).

The goal of the present study was the reconstruction of accident doses for SNTS area inhabitants using EPR measurements of teeth. The purpose of the measurements is to support an ongoing epidemiologic study presently being conducted by the US National Cancer Institute (NCI).

Section snippets

Phases of study

EPR measurements were made in two phases (2002 (see Desrosiers, 2003) and in 2005) at the US National Institute of Standards and Technology (NIST) and the Ukrainian Scientific Center for Radiation Medicine. Doses for 103 persons from nine settlements were reconstructed using EPR measurements. While similar equipment was used, there were modest differences in techniques and spectra interpretation procedures.

Teeth

Seventy-two teeth (both molars and front teeth) were measured in 2002 and 32 molars were

Results and discussion

Seventy-six lateral teeth and 27 front teeth were measured from 103 inhabitants of eight villages and one city near to the SNTS. Summary statistics of the accident doses reconstructed by EPR methods, as described earlier, are presented in Table 1.

A comparison of dose estimates to lateral teeth, stratified by village of residence at the time of tooth extraction, distinguished two groups based on similar median doses. One group was defined by village-median doses in the range of 30–60 mGy

Conclusions

External doses to teeth from exposure to residual fallout radioactivity from the SNTS were determined by the EPR technique for inhabitants of nine settlements located near to the Semipalatinsk nuclear test site. The nuclear tests-related doses ranged from zero up to approximately 2 Gy, excluding one case of about 9 Gy that in all likelihood was the result of radiotherapy as a medical treatment.

A high variability among teeth from within each village was found while differences between village

Acknowledgments

This work was supported by the US National Cancer Institute and the National Institute of Allergy and Infectious Diseases, Program on Medical Countermeasures Against Radiological and Nuclear Threats (NIAID agreement #Y2-AI-5077 and NCI agreement #Y3-CO-5117). The authors want to thank Dr. Boris Gusev (Kazakh Research Institute for Radiation and Medical Ecology) for providing tooth samples that were used for EPR analysis.

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Reflections on the future developments of research in retrospective physical dosimetry
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The radiation markers for dosimetry were required to be stable over the years and apparent at doses relevant for the stochastic effects, i.e., of the order of hundreds of mGy. Tooth enamel with EPR and construction bricks with TL/OSL, having these characteristics, were used to assess, respectively, the individual and environmental dose in survivors of atomic bomb attacks in Japan [17], in populations of villages and workers of the Mayak nuclear plant in the former Soviet Union [18,19], Chernobyl liquidators [20,21], and in nuclear testing sites at Semipalatinsk [22,23]. In parallel and since the early days, EPR and to a lesser extent TL have been applied in so-called small-scale events (International Atomic Energy Agency (IAEA) [24–29], with small number of individuals affected and short range release, which are actually those classified as IAEA INES levels 1–4 [30].
Electron paramagnetic resonance, thermoluminescence, and optically stimulated luminescence, with biological tissues and inert materials are well established physical methods for retrospective dosimetry in acute accidental exposures. The objective of this article is to provide a view of the questions still open, the current challenges and the needed solutions. As research on emergency response methods is encountering increasing difficulties in terms of financial and human resources in many countries, it is essential to identify the research priorities and pay attention to cost-effective research paths. The intention of the paper is to stimulate discussion in the scientific community and to encourage collaboration among laboratories toward goals that address the real needs in retrospective dosimetry for acute exposures.
ESR tooth enamel retrospective dosimetry quoted as spin numbers
2020, Radiation Measurements
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Through several intercomparison studies (Chumak et al., 1996; Wieser et al., 2000, 2005; 2006; Hoshi et al., 2007; Ivannikov et al., 2007; Fattibene et al., 2011), the method of ESR human tooth enamel dosimetry is now an established method so that an ISO international standard was published (ISO, 2013). When determining a retrospective dose of a sample of interest, the calibration method has been applied in most of the studies referred above as well as the additive dose method in some studies (Shishkina et al., 2016; Sholom et al., 2007; Ikeya et al., 1984). Currently, each laboratory working on ESR tooth enamel dosimetry using the calibration method has a set of standard samples of irradiated human tooth enamel.
Instead of using a set standard samples of irradiated tooth enamel, retrospective doses to tooth enamel can be estimated by ESR (electron spin resonance, or EPR) dosimetry with the spin numbers. The efficiency factor (the sensitivity to gamma ray dose) of the dosimetric CO₂⁻ ESR signal in tooth enamel was tentatively obtained, using a diluted tempol benzene solution, to be 8.73 × 10¹⁶ spin/J (spin/kg/Gy), being equivalent to a G value (a spin number formed per 100 eV of absorbed energy) of 1.40. When a dosimetric system in a laboratory is calibrated with a standard with known spin numbers such as tempol, retrospective ESR tooth enamel ESR dosimetry is done without a set of irradiated tooth enamel standard samples.
Retrospective and emergency dosimetry in response to radiological incidents and nuclear mass-casualty events: A review
2016, Radiation Measurements
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For some residents of Dolon, calculations of individual external doses were also performed (based on the data derived from individual questioning), which demonstrated a much better correlation with corresponding EPR doses. An average EPR dose 222 ± 131 mGy was obtained for 13 residents of Dolon by another research team (Sholom et al., 2007a). In that study, tooth doses were reconstructed for 103 people from 9 settlements with all studied teeth having been formed before the first nuclear test in 1949.
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.
EPR and OSL emergency dosimetry with teeth: A direct comparison of two techniques
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Tooth enamel is well established as a reliable Electron Paramagnetic Resonance (EPR) dosimeter. It was used for the dose reconstruction of A-bomb victims in Japan (Ikeya et al., 1984); Chernobyl Nuclear Power Plant liquidators in Ukraine and Russia (Chumak et al., 1999; Skvortsov et al., 2000); Mayak Nuclear Facility workers in Russia (Romanyukha et al., 1994); Techa river population in Russia (Romanyukha et al., 2001); and the Semipalatinsk Nuclear Test Site region population in Kazakhstan (Sholom et al., 2007). The main advantage of the tooth EPR dosimetry technique is the high stability of the enamel dosimetric EPR signal, which is mainly attributed to CO2- radicals (Vanhaelewyn et al., 2002).
The OSL dosimetry technique with teeth has been validated against the EPR dosimetry technique through a measurement comparison performed on the same teeth. The OSL reconstructed doses were found to be in agreement with corresponding EPR doses. Minimum measurable doses for the OSL technique were estimated to be in the range 0.9–1.5 Gy for measurements made within 24 h post-exposure if OSL signals are collected from 6 teeth at the same time. These values satisfy the requirements for emergency triage dosimetry. The fading of tooth OSL signals correlated with fading of radiation-induced EPR signals observed at g = 2.0115 that are attributed to CO₃^- radicals. OSL sensitivity can be enhanced if more teeth from the same individual will be used for the signal accumulation.
Retrospective dosimetry assessment using the 380 °c thermoluminescence peak of tooth enamel
2011, Radiation Measurements
The thermoluminescence (TL) response to gamma-ray irradiation of tooth enamel is reported. The tooth enamel was separated from dentine by using mechanical and physico-chemical procedures followed by grinding (grain size ∼100 μm) and etching. The TL was attributed to the recombination of ${CO}_{2}^{-}$ radicals incorporated into or attached to the surface of hydroxyapatite crystals. The growth of the ∼380 °C TL peak with absorbed dose was examined with irradiated tooth enamel samples and reconstructed doses evaluated for tooth enamel samples from four human subjects.
BiodosEPR-2006 consensus committee report on biodosimetric methods to evaluate radiation doses at long times after exposure
2007, Radiation Measurements
The requirements for biodosimetric techniques used at long times after exposure, i.e., 6 months to more than 50 years, are unique compared to the requirements for methods used for immediate dose estimation. In addition to the fundamental requirement that the assay measures a physical or biologic change that is proportional to the energy absorbed, the signal must be highly stable over time to enable reasonably precise determinations of the absorbed dose decades later. The primary uses of these biodosimetric methods have been to support long-term health risk (epidemiologic) studies or to support compensation (damage) claims. For these reasons, the methods must be capable of estimating individual doses, rather than group mean doses. Even when individual dose estimates can be obtained, inter-individual variability remains as one of the most difficult problems in using biodosimetry measurements to rigorously quantify individual exposures. Other important criteria for biodosimetry methods include obtaining samples with minimal invasiveness, low detection limits, and high precision. Cost and other practical limitations generally prohibit biodosimetry measurements on a large enough sample to replace analytical dose reconstruction in epidemiologic investigations. However, these measurements can be extremely valuable as a means to corroborate analytical or model-based dose estimates, to help reduce uncertainty in individual doses estimated by other methods and techniques, and to assess bias in dose reconstruction models. There has been extensive use of three biodosimetric techniques in irradiated populations: EPR (using tooth enamel), FISH (using blood lymphocytes), and GPA (also using blood); these methods have been supplemented with luminescent methods applied to building materials and artifacts. A large number of investigations have used biodosimetric methods many years after external and, to a lesser extent, internal exposure to reconstruct doses received from accidents, from occupational exposures, from environmental releases of radioactive materials, and from medical exposures. In most applications, the intent has been to either identify highly exposed persons or confirmed suspected exposures. Improvements in methodology, however, have led many investigators to attempt quantification of whole-body doses received, or in a few instances, to estimate organ doses. There will be a continued need for new and improved biodosimetric techniques not only to assist in future epidemiologic investigations but to help evaluate the long-term consequences following nuclear accidents or events of radiologic terrorism.

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EPR tooth dosimetry of SNTS area inhabitants

Abstract

Introduction

Section snippets

Phases of study

Teeth

Results and discussion

Conclusions

Acknowledgments

Appl. Radiat. Isot.

Rad. Meas.

The application of retrospective luminescence dosimetry in areas affected by fallout from the Semipalatinsk nuclear test site: an evaluation of potential

Health Phys.

Biodosimetry study in Dolon and Chekoman villages in the vicinity of the semipalatinsk nuclear test site

J. Radiat. Res.

Application of high precision EPR dosimetry with teeth for reconstruction of doses to Chernobyl populations

Radiat. Prot. Dosim.

Retrospective dose assessment for the population living in areas of local fallout from the semipalatinsk nuclear test site, Part 1: external exposure

J. Radiat. Res.