Estimating individual thyroid doses for a case-control study of childhood thyroid cancer in Bryansk Oblast, Russia.

Following the Chernobyl accident, radioactive fission products, including (131)I and (137)Cs, were deposited in Bryansk Oblast in Russia. Intakes of radioiodines, mainly (131)I in milk, were the principal sources of radiation doses to thyroids of residents of the contaminated areas, but those radionuclides decayed before detailed contamination surveys could be performed. As a result, (137)Cs deposition density is the primary measure of the contamination due to the accident and there are relatively few measurements of the ratio of (131)I to (137)Cs in vegetation or soil samples from this area. Although many measurements of radiation emitted from the necks of residents were performed and used to estimate thyroidal (131)I activities and thyroid doses, such data are not available for all subjects. The semi-empirical model was selected to provide a dose calculation method to be applied uniformly to cases and controls in the study. The model was developed using dose estimates from direct measurements of (131)I in adult thyroids, and relates settlement average thyroid doses to (137)Cs contamination levels and ratios of (131)I to (137)Cs. This model is useful for areas where thyroid monitoring was not performed and can be used to estimate doses to exposed individuals. For application to children in this study, adjustment factors are used to address differences in age-dependent intake rates and thyroid dosimetry. Other individual dietary factors and sources (private/public) of milk consumed are reflected in the dose estimates. Countermeasures that reduced thyroid dose, such as cessation of milk consumption and intake of stable iodine, are also considered for each subject. The necessary personal information of subjects was obtained by interview, most frequently of their mothers, using a questionnaire developed for the study. Uncertainties in thyroid dose, estimated using Monte Carlo techniques, are presented for reference conditions. Thyroid dose estimates for individual children made using the semi-empirical model and questionnaire data compare reasonably well with dose estimates made for 19 children whose thyroid burdens of (131)I were measured from May to June 1986.

Possibility of using porcelain samples of high-voltage line insulators for radiation dose reconstruction by EPR spectroscopy.

In electron paramagnetic resonance spectra of irradiated porcelain samples from high-voltage supply line insulators three overlapping single signals were observed. The dependencies of the amplitude of these signals on the microwave power, irradiation dose and the stability in darkness and in natural light were investigated. It was concluded that for dosimetric purposes it is reasonable to use the radiation-induced signal with g = 2.001, which could be ascribed to the E' centres of quartz. The microwave power dependence of the amplitude of this signal is saturated at 1 mW, the dose dependence is saturated at about 60 mGy. A minimal level of dose determination is about 1 Gy, and it is limited mainly by the accuracy of subtraction of the background signal existing in the unirradiated sample. The radiation-induced signal is stable in the darkness, but rapidly faded in natural light, therefore, for dosimetric purposes it is possible to use only insulators covered with dark glaze or ceramic samples from the very interior of the insulators.

Dosimetry studies in Zaborie village.

Dosimetry studies in Zaborie, a territory in Russia highly contaminated by the Chernobyl accident, were carried out in July, 1997. Studies on dosimetry for people are important not only for epidemiology but also for recovery of local social activity. The local contamination of the soil was measured to be 1.5-6.3 MBq/m2 of Cs-137 with 0.7-4 microSv/h of dose rate. A case study for a villager presently 40 years old indicates estimations of 72 and 269 mSv as the expected internal and external doses during 50 years starting in 1997 based on data of a whole-body measurement of Cs-137 and environmental dose rates. Mean values of accumulated external and internal doses for the period from the year 1986 till 1996 are also estimated to be 130 mSv and 16 mSv for Zaborie. The estimation of the 1986-1996 accumulated dose on the basis of large scale ESR teeth enamel dosimetry provides for this village, the value of 180 mSv. For a short term visitor from Japan to this area, external and internal dose are estimated to be 0.13 mSv/9d (during visit in 1997) and 0.024 mSv/50y (during 50 years starting from 1997), respectively.

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.

ESR and TL dosimetry systems: comparative measurements for human phantom.

Mixtures of small fragments of tooth enamel as well as thermoluminescence (TL) dosimeters were placed into the tissue-equivalent phantom of the human head with skeleton (approximately at the level of the jaws) and irradiated using 137Cs low dose-rate gamma therapeutic sources ('SELEKTRON' LDR 137Cs). Phantom, samples of teeth and TL detectors were irradiated behind water tank to produce scattered irradiation. The same irradiation with the same geometry was performed in air too. For gamma-spectrometry 137Cs sources with very low activity were used but with the same geometry as therapeutic sources. The absorbed dose in enamel was estimated with the help of ESR spectrometer 'ESP-300 E' (Brucker). The samples of tooth enamel were partially used for preliminary dose evaluation by ESR signal before starting of experiment. TL dosimetry was performed by TL reader model 8800 (HARSHAW) using TL dosimeters calibrated with 137Cs. The paper presents data obtained in comparative aspects.