The Chernobyl accident: EPR dosimetry on dental enamel of children.

The radiation dose on tooth enamel of children living close to Chernobyl has been evaluated by EPR. The sample preparation was reduced to a minimum of mechanical steps to remove a piece of enamel. A standard X-ray tube at low energy was used for additive irradiation. The filtration effect of facial soft tissue was taken into account. The radiation dose for a group of teeth slightly exceeds the annual dose, whereas for another group the dose very much exceeds the annual dose. Since the higher dose is found in teeth whose enamel have much lower EPR sensitivity to the radiation, it can be suggested that for these teeth the native signal could alter the evaluation of the smaller radiation signal.     

Biophysical dose measurement using electron paramagnetic resonance in rodent teeth.

Electron paramagnetic resonance (EPR) dosimetry of human tooth enamel has been widely used in measuring radiation doses in various scenarios. However, there are situations that do not involve a human victim (e.g. tests for suspected environmental overexposures, measurements of doses to experimental animals in radiation biology research, or chronology of archaeological deposits). For such cases we have developed an EPR dosimetry technique making use of enamel of teeth extracted from mice. Tooth enamel from both previously irradiated and unirradiated mice was extracted and cleaned by processing in supersaturated KOH aqueous solution. Teeth from mice with no previous irradiation history exhibited a linear EPR response to the dose in the range from 0.8 to 5.5 Gy. The EPR dose reconstruction for a preliminarily irradiated batch resulted in the radiation dose of (1.4+/-0.2) Gy, which was in a good agreement with the estimated exposure of the teeth. The sensitivity of the EPR response of mouse enamel to gamma radiation was found to be half of that of human tooth enamel. The dosimetric EPR signal of mouse enamel is stable up at least to 42 days after exposure to radiation. Dose reconstruction was only possible with the enamel extracted from molars and premolars and could not be performed with incisors. Electron micrographs showed structural variations in the incisor enamel, possibly explaining the large interfering signal in the non-molar teeth.     

Comparison of sample preparation and signal evaluation methods for EPR analysis of tooth enamel.

In dose reconstruction by EPR dosimetry with teeth various methods are applied to prepare tooth enamel samples and to evaluate the dosimetric signal. A comparison of seven frequently used methods in EPR dosimetry with tooth enamel was performed. The participating Institutes have applied their own procedure to prepare tooth enamel samples and to evaluate the dosimetric signal. The precision of the EPR measurement and the dependence of the estimated dosimetric signal with irradiation up to 1000 mGy were compared. The obtained results are consistent among the different methods. The reproducibility of the dosimetric signal and its estimated relation with the absorbed dose was found to be very close for the applied methods with one possible exception.     

Preliminary report on the development of a virtually nondestructive additive dose technique for EPR dosimetry.

We propose a new approach to the additive dose method in EPR dosimetry studies for tooth enamel specimens. We outline a specialized routine whereby the sample may be left for the most part unirradiated, while only a small aliquot of the sample will be additively irradiated to relatively large doses. The routine is done in such a way so as not to significantly compromise either precision or accuracy of the dose reconstruction. It is also demonstrated that the overall throughput of the dose reconstruction is not appreciably compromised. With this potential ability, the utility of an international dose/sensitivity standard for EPR dosimetry of teeth is considered.     

Parameters affecting EPR dose reconstruction in teeth.

The aim of this paper is to analyze the lower limit of detection (LLD), linearity of dose response, variation of radiation sensitivity between different tooth enamel samples, and time/temperature stability of EPR biodosimetry in tooth enamel. The theoretical LLD is shown to be 0.46 mGy, which is far lower than the measured value of about 30 mGy. The main issues to lowering LLD are the differentiation of the radiation-induced component against the total EPR spectrum and the complex nature of the dose dependence of the EPR signal. The following questions are also discussed in detail: need for exfoliated or extracted teeth from persons of interest, accounting for background radiation contribution; conversion of tooth enamel absorbed dose to effective dose; accounting for internal exposure specifically from bone-seeking radionuclides. Conclusions on future development of EPR retrospective biodosimetry are made.     

不同制备方法对牙釉质样品ESR信号的影响

目的研究不同制备方法对牙釉质样品ESR信号的影响，有效地提高牙釉质样品ESR剂量学的灵敏度。方法对无放射线照射史成年人臼齿分别用化学、机械以及机械加化学方法进行处理，制备牙釉质样品。利用电子自旋共振仪测定不同制备方法处理的样品在^60Coγ射线照射不同剂量后的ESR信号。比较分析其灵敏度，从而寻求一种对牙釉质样品ESR信号影响较小的样品制备及处理方法。结果不同方法处理的牙釉质样品的ESR信号，对^60Coγ射线的响应有较明显的差异。结论利用牙釉质ESR剂量学重建受照人员剂量时，尤其是使用附加照射法进行较低剂量重建时，选择合适的样品制备方法是十分重要的。     

Mechanically induced EPR signals in tooth enamel.

Sample preparation of tooth enamel for electron paramagnetic resonance (EPR) dosimetry usually involves mechanical operations. The present study shows that mechanical operations performed without water cooling generate a paramagnetic center inducing a stable isotropic EPR signal with g-value of 2.00320 and linewidth of about 0.1 mT. Using EPR spectrum simulation, the similarity between the mechanically induced signal and the signal generated when the enamel is heated in air at a temperature above 600 degrees C was investigated. Results indicate that the mechanically induced signal is related to sample temperature increase during mechanical friction.     

Tooth enamel EPR dosimetry: sources of errors and their correction.

Some of the most important sources of systematic errors in dose determination using tooth enamel EPR spectroscopy and ways of reducing those errors are discussed. Enamel from the outside of the front teeth should not be used for dose determination because of induction of paramagnetic centers by solar light. The accuracy of the method in the low dose range is limited by variation in the shape of the EPR signal of unirradiated enamel, which can be described by an initial intrinsic signal and which varies for different samples with standard deviation of 20-30 mGy. The energy dependence of enamel sensitivity should be taken into account in the form of a correction factor. The value of this factor is estimated at 1.1-1.3 for real radiation fields in radiation contaminated territories. Variation in enamel sensitivity for different samples is shown to be within limits of 10-15% of the average value.     

Metabolism in tooth enamel and reliability of retrospective dosimetry.

Most of the radiation centers in tooth enamel and bones are formed by the reactions COOH + gamma-->CO2- + H+, and CO2 + e- -->CO2-. These centers can be easily changed by metabolism and have a low stability in living organisms. The efficiency of CO2- radical production by irradiation is substantially different for teeth and bones in living rat, dead rat, and teeth and bone removed from rat. It is shown that the suitability of tooth enamel for retrospective dosimetry can be evaluated from the anisotropy of its EPR signals.     

EPR dosimetry with tooth enamel: A review

When tooth enamel is exposed to ionizing radiation, radicals are formed, which can be detected using electron paramagnetic resonance (EPR) techniques. EPR dosimetry using tooth enamel is based on the (presumed) correlation between the intensity or amplitude of some of the radiation-induced signals with the dose absorbed in the enamel. In the present paper a critical review is given of this widely applied dosimetric method. The first part of the paper is fairly fundamental and deals with the main properties of tooth enamel and some of its model systems (e.g., synthetic apatites). Considerable attention is also paid to the numerous radiation-induced and native EPR signals and the radicals responsible for them. The relevant methods for EPR detection, identification and spectrum analyzing are reviewed from a general point of view. Finally, the needs for solid-state modelling and studies of the linearity of the dose response are investigated. The second part is devoted to the practical implementation of EPR dosimetry using enamel. It concerns specific problems of preparation of samples, their irradiation and spectrum acquisition. It also describes how the dosimetric signal intensity and dose can be retrieved from the EPR spectra. Special attention is paid to the energy dependence of the EPR response and to sources of uncertainties. Results of and problems encountered in international intercomparisons and epidemiological studies are also dealt with. In the final section the future of EPR dosimetry with tooth enamel is analyzed.     

Application of EPR retrospective dosimetry for large-scale accidental situation.

Above 3000 tooth enamel samples, collected at population of radioactive contaminated territories after Chernobyl accident, the Chernobyl liquidators, the retired military of high radiation risk and the population of control radiation free territories were investigated by EPR spectroscopy method in order to obtain accumulated individual exposure doses. Results of EPR spectra measurements are stored in data bank; enamel samples are also stored in order to provide the possibility to repeat the measurements in future. Statistical analysis of results has allowed to detect the contribution into EPR signal in tooth enamel due to the action of the natural background radiation, and the radioactive contamination of territory. In general, the average doses of external exposure of the population obtained with EPR spectroscopy of teeth enamel are consistent with results based on other methods of direct and retrospective dosimetry. Essential exceeding of the individual doses above the average level within the population groups was observed for some persons. That gave the possibility to detect the individuals with overexposure, which were included into groups for medical monitoring.     

New computer procedure for routine EPR-dosimetry on tooth enamel: description and verification.

A software code was developed for fitting the EPR tooth enamel spectrum using linear combinations of Gaussian functions. The software is fastening EPR dose reconstruction for routine applications. The verification of the software was done comparing with the selective saturation method as an independent procedure of signal evaluation. Both methods were applied for the dose reconstruction of 13 teeth mostly from the Techa riverside. The evaluated doses by the two methods demonstrate an excellent agreement.     

EPR dose reconstruction for bone-seeking 90Sr.

The results of the EPR dose reconstruction in calcified tissues of dog injected with 90Sr are presented. It has been established that there is no essential difference in the values of doses absorbed in tooth tissues of teeth in symmetric positions in the mouth, whereas a significant difference occurs in the values of absorbed doses in teeth in non-symmetric positions. In the case of 90Sr internal exposure the dose reconstruction in crown dentine plays an important role. It has been found that its quantity is close to the dose in diaphyseal cortical bone of the femur, dose at the endosteal bone surface and in femural fatty marrow. The fact that these values exceed doses absorbed in tooth enamel points out the predominant contribution of internal exposure. The highest absorbed doses have been observed in metaphyseal trabecular femur bones, tooth alveolar bone walls, and cortical and trabecular vertebra that can be considered as suitable candidates for biomarkers of internal 90Sr exposure for post-mortal autopsy. The satisfactory correlation has been found between the doses reconstructed in calcified dog tissues and the doses measured by EPR in alanine dosimeters fixed in (or nearby) the sites of autopsy of bones/teeth. The experiments provide support for the view that EPR retrospective dosimetry with calcified tissues for internal exposure is unique in providing useful information on the doses obtained.     

Separation of the contributions from gamma- and UV-radiation to the EPR spectra of tooth enamel plates.

Anisotropy of EPR spectra of tooth enamel plates irradiated with gamma-rays and UV light has been studied. UV-irradiated enamel plates exhibit a stronger anisotropy than gamma-irradiated plates. Investigation of samples cut out of different teeth and irradiated to different doses showed that the value of anisotropy is characteristic of each type of irradiation; it equals to approximately 0.35 for gamma- rays and 0.50 for UV light. It is suggested that the difference in the anisotropy values can be attributed to different relative amounts of oriented and disordered radicals produced by the two types of radiation. This can be used for separating gamma- and UV-contributions to the total EPR signal of a tooth exposed to both types of radiation.     

山羊牙釉质电子自旋共振的剂量学特性

目的 探讨山羊牙釉质电子自旋共振(ESR)的剂量学的特性.方法 采用机械和化学处理相结合的方法,制备5组不同年龄的山羊牙釉质样品.用137 Cs γ射线照射山羊牙釉质样品,使用ESR波谱仪测量辐射前和不同辐射剂量后不同牙釉质样品的ESR信号.结果 137Cs γ射线照射前,山羊牙釉质所固有的ESR本底信号平均值为21.5,明显低于人的平均本底强度水平39.5;与人牙釉质相同,山羊牙釉质照射后产生的剂量学信号的强度与照射剂量线性相关,5组100 mg山羊牙釉质样品,其剂量学峰的辐射灵敏度的平均值为(34.3±1.9)/Gy,与人牙釉质样品的辐射响应平均值36.3/Gy非常接近.结论 人类牙釉质样品缺乏时,可以用相同辐射环境中的山羊牙釉质作为替代品进行剂量重建,为正确地评价辐射事故剂量提供科学依据.

Abstract：

Objectlve To study the properties of goat tooth enamel electron spin resonance (ESR)dosimetry.Methods Tootll enamel samples of goats were achieved by combined mechanical and chemical treatment at the ages of l,2,3,5,and 6 years.respectively and 9 enamel samples of adult molar were obtained.These enamel samples were exposed to 137Cs γ-rays at the cumulative doses of 0,0.5,1.0,2.0,and 5.0 Gy,respectively.ESR spectra Was measured before and after exposure.Results The background signal of goat tooth samples W88 21.5,significantly lower than that of the adult molar samples(39.5).The dusimetric signal intensity of the goat enamel increased with the radiation dose in a linear manner just as that of the human molars.The average radiation sensitivity of the goat tooth samples was(34.3±1.9)/Gy,close to that of the human tooth samples.Conclusions Goat teeth can be used for retrospective radiation dose reconstruction when human teeth are unavailable,in order to previde scientific data for dose reconstruction accurately.     

Anisotropy effects of EPR signals and mechanisms of mass transfer in tooth enamel and bones.

Peculiarities of the internal construction of tooth enamel and bones that cause anisotropy effects and mass transfer in these objects are described. It is shown that the composition of the mineral component of teeth and bones depends on a mechanical-electrical mechanism, which pumps ions into nanocrystals. Decrease in the efficiency of the mechanical-electrical mechanism results in demineralization of enamel and bones, which progresses most rapidly at a disease of the biomineral or under special conditions, such as in space flights. Effects of signal anisotropy in the practice of retrospective EPR dosimetry are discussed.     

Retrospective radiation dosimetry using electron paramagnetic resonance in canine dental enamel.

Electron paramagnetic resonance (EPR) biodosimetry of human tooth enamel has been widely used for measuring radiation doses in various scenarios. We have now developed EPR dosimetry in tooth enamel extracted from canines. Molars and incisors from canines were cleaned by processing in supersaturated aqueous potassium hydroxide solution. The dosimetric signal in canine tooth enamel was found to increase linearly as a function of laboratory added dose from 0.44+/-0.02 to 4.42+/-0.22 Gy. The gamma radiation sensitivity of the canine molar enamel was found to be comparable to that of human tooth enamel. The dosimetric signal in canine enamel has been found to be stable up to at least 6 weeks after in vitro irradiation. A dosimetric signal variation of 10-25% was observed for canines ranging from in age 3 years to 16 year old.     

Optimal registration conditions for tooth EPR dosimetry at low accumulated dose

The spectrum registration under rapid passage conditions (the second harmonic phase quadrature of the absorption signal) allows one to enhance substantially the sensitivity of tooth enamel and bone EPR dosimetry at a low accumulated dose. In the present work the dependencies of the radiation and background signals on EPR spectrometer parameters are described and the optimal conditions in RPM for EPR dosimetry are obtained.     

对辐照牙釉质EPR谱数学模拟的研究

目的　建立辐照牙釉质EPR谱数学模拟方法。方法　采用高斯函数一阶微商作为基本的模型函数 ,编写基于Marquardt Levenberg非线性最小二乘法曲线拟合算法的计算程序模拟辐照牙釉质EPR谱 ,并检验拟合精度。结果　对 2 70和 84 0mGy辐照的牙釉质样品的EPR复合谱 ,拟合后的残谱分别为 - 1 6 1± 2 3 5 9和 - 3 77± 2 4 94 ,残谱均值和标准差分别占各自峰高的 0 3%、3 8%和 0 4 %、3%。结论　这种算法和模型函数能很好地模拟辐照牙釉质EPR复合谱。     

牙釉质电子顺磁共振剂量重建研究的若干进展

介绍了牙釉质电子顺磁共振回顾性剂量学的目前研究概况,着重阐述了低剂量区去除背景信号的新方法,同时也对其在体测量及紫外线影响等方面进行了讨论。