Valeriy Stepanenko

Measurement of absorbed doses from X-ray baggage examinations to tooth enamel by means of ESR and glass dosimetry

The contribution of radiation from X-ray baggage scans at airports on dose formation in tooth samples was investigated by electron spin resonance (ESR) dosimetry and by glass dosimetry. This was considered important, because tooth samples from population around the Semipalatinsk Nuclear Test Site (SNTS), Kazakhstan, had been transported in the past to Hiroshima University for retrospective dose assessment of these residents. Enamel samples and glass dosimeters were therefore examined at check-in time at Kansai airport (Osaka, Japan), Dubai airport (Dubai, United Arab Emirates) and Domodedovo airport (Moscow, Russia). These airports are on the route from Kazakhstan to Japan. Three different potential locations of the samples were investigated: in pocket (without X-ray scans), in a small bag (with four X-ray scans) and in large luggage (with two X-ray scans). The doses obtained by glass and ESR dosimetry methods were cross-compared. As expected, doses from X-ray examinations measured by glass dosimetry were in the μGy range, well below the ESR detection limit and also below the doses measured in enamel samples from residents of the SNTS.

ESR dosimetry study of population in the vicinity of the Semipalatinsk Nuclear Test Site

A tooth enamel electron spin resonance (ESR) dosimetry study was carried out with the purpose of obtaining the individual absorbed radiation doses of population from settlements in the Semipalatinsk region of Kazakhstan, which was exposed to radioactive fallout traces from nuclear explosions in the Semipalatinsk Nuclear Test Site and Lop Nor test base, China. Most of the settlements are located near the central axis of radioactive fallout trace from the most contaminating surface nuclear test, which was conducted on 29 August 1949, with the maximum detected excess dose being 430 ± 93 mGy. A maximum dose of 268 ± 79 mGy was determined from the settlements located close to radioactive fallout trace resulting from surface nuclear tests on 24 August 1956 (Ust-Kamenogorsk, Znamenka, Shemonaikha, Glubokoe, Tavriya and Gagarino). An accidental dose of 56 ± 42 mGy was found in Kurchatov city residents located close to fallout trace after the nuclear test on 7 August 1962. This method was applied to human tooth enamel to obtain individual absorbed doses of residents of the Makanchi, Urdzhar and Taskesken settlements located near the Kazakhstan–Chinese border due to the influence of nuclear tests (1964–1981) at Lop Nor. The highest dose was 123 ± 32 mGy.

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.

EPR DOSIMETRY STUDY FOR POPULATION RESIDING IN THE VICINITY OF FALLOUT TRACE FOR NUCLEAR TEST ON 7 AUGUST 1962

The method of electron paramagnetic resonance (EPR) dosimetry using extracted teeth has been applied to human tooth enamel to obtain individual absorbed doses of residents of settlements in the vicinity of the central axis of radioactive fallout trace from the contaminating surface nuclear test on 7 August 1962. Most of the settlements (Kurchatov, Akzhar, Begen, Buras, Grachi, Mayskoe, Semenovka) are located from 70 to 120 km to the North-East from the epicenter of the explosion at the Semipalatinsk Nuclear Test Site (SNTS). This region is basically an agricultural region. A total of 57 teeth samples were collected from these sites. Eight teeth from residents of the Kokpekty settlement, which was not subjected to any radioactive contamination and located 400 km to the Southeast from SNTS, were chosen as a control. The principal findings, using this method, were that the average excess dose obtained after subtraction of the natural background radiation was 13 mGy and ranged up to about 100 mGy all for residents in this region.

Comparison of calculated beta- and gamma-ray doses after the Fukushima accident with data from single-grain luminescence retrospective dosimetry of quartz inclusions in a brick sample

Abstract To estimate the beta- and gamma-ray doses in a brick sample taken from Odaka, Minami-Soma City, Fukushima Prefecture, Japan, a Monte Carlo calculation was performed with Particle and Heavy Ion Transport code System (PHITS) code. The calculated results were compared with data obtained by single-grain retrospective luminescence dosimetry of quartz inclusions in the brick sample. The calculated result agreed well with the measured data. The dose increase measured at the brick surface was explained by the beta-ray contribution, and the slight slope in the dose profile deeper in the brick was due to the gamma-ray contribution. The skin dose was estimated from the calculated result as 164 mGy over 3 years at the sampling site.

The experience of individual dose reconstruction after uncontrolled large-scale irradiation of population

There are three main methods available to obtain retrospective assessments of radiation dose: a) computational modeling (CM), which use archive monitoring data of radioactive contamination of soils, biota and human body are applied to develop radioecological models for estimation of mean doses. Individualization of mean calculated doses is performed using results of individual questioning of the inhabitants of the contaminated territories. The evaluation of the uncertainty of doses is provided by Monte Carlo method with a variation of parameters of the models; b) the retrospective luminescence dosimetry (RLD) and c) ESR dosimetry, determine the cumulative absorbed dose in the bricks of buildings and in human tooth enamel, respectively. RLD and ESR dosimetry methods allow the estimation of accumulated dose with accuracy of 20-30 mGy Estimates of dose obtained by applying CM, RLD and ESR methods downwind the Chernobyl NPP and to Semipalatinsk nuclear test site (SNTS) are overviewed in the paper. The comparisons of dose estimates by different methods are pesented. Key technologies, methods and equipment, application areas, technology target, methods developed, categories of investigated subjects are the following: Key approaches and technologies. Radioecological models and individual dosimetrical questionnaires for individual dose estimations by modeling calculations (MC), Retrospective Luminescence Dosimetry (RLD) with quartz inclusions, Electron Spin Resonance (ESR) dosimetry with human tooth enamel; Methods and equipment. RISOE luminescence reader, Brucker ESR spectrometer, know-how spectra processing software, know-how sampling and sample preparation methodology. Application areas: -Individual retrospective dosimetry in support to radiation epidemiological studies; -Retrospective dosimetry in support to making decision regarding mitigation of the health consequences of large scale radiation accidents; -Retrospective dosimetry in a case of local radiation accidents with radioactive sources; -Retrospective instrumental estimation of radiation doses in a cases of uncontrolled (accidental) irradiation of personnel or patients in a course or radiation therapy. Target: to develop and to harmonize the system of methods of retrospective dosimetry for national and worldwide distribution. Methods developed: radioecological models and individual dosimetrical questionnaires for individual dose estimations by modeling calculations; retrospective luminescence dosimetry with quartz inclusions in the bricks of the buildings; retrospective ESR dosimetry with human tooth enamel. Categories of investigated subjects: Population of territories contaminated following the Chernobyl accident (Russian Federation) – Fig. 1.; Population of territories around Semipalatinsk nuclear test site (Russian Federation and Republic of Kazakhstan)Fig. 2. Fig.1. Example [1,2]. Map with indication of raions of Bryansk oblast (Russian Federation), which were contaminated resulting the Chernobyl accident. 221 km of distance from Chernobyl NPP to the most contaminated settlement Zaborie village (soil contamination density by 137 Cs 4300 kBq/m 2 ). Fig.2. Example [3]. The 1st A-bomb test in former USSR (29.08.1949) – the radioactive trace in Kazakhstan and Russia with indication of investigated settlements. NTS – Semipalatinsk nuclear test site. Monitoring of 131 I activity in thyroid gland and development of thyroid dose reconstruction approach among inhabitants of territories contaminated by radionuclides as a result of the Chernobyl accident (Russian Federation). During May of 1986 the massive monitoring of 131 I activity in thyroid gland among inhabitants of Russian territories contaminated by radionuclides as a result of Chernobyl accident was performed [4,5]. During 3 weeks on May of 1986 26 724 inhabitants of 115 contaminated settlements of 7 subregions (raions) were monitored in Kaluga region (RF) [6]. The detailed description of developed technology of dose monitoring and of methods of thyroid dose estimations are presented in [4,5,7]. Individual thyroid doses were estimated for each monitored person with accounting for real dose forming factors on May of 1986 year [6]. As to Kaluga region, the maximal thyroid doses were estimated in 3 contaminated subregions – Ul’ianovoskiy, Zhsizdrinskiy, Khvastovochskiy (see Table 1 as well for 7 investigated subregions in total [5]). It was found on the early stage of investigation (1986 year) that statistical distribution of individual thyroid doses is characterized by “long tail” in the individual dose range, which is much higher than mean and median doses for different age groups [4]. Table 1. Example [5]. Thyroid absorbed doses in different age groups of investigated inhabitants of 7 subregions of Kaluga region. *) N-number of investigated persons; MID-maximal individual dose; DA-average dose for given age group; DM-median dose for given age group; GSDgeometric standard deviation. The results of massive monitoring of thyroid doses among inhabitants of contaminated territories of Kaluga region were combined with the similar data related to contaminated territories of Bryansk region (Russia) and Republic of Belarus. As a result the individual thyroid dose reconstruction approach was developed for persons who were not monitored just after the accident (on May, 1986): it is radioecological semiempirical model and individual dosimetrical questionnaires for individual dose estimations by modeling calculations [4,5,7-10]. The developed approach of individual thyroid dose reconstruction is still actual for implementation in a cases of possible large scale radiations accidents. Figure 3 shows an example of comparison of individual thyroid doses: calculated individual thyroid doses VS dose estimations based on the results of 131 I measurements in thyroid gland among inhabitants of contaminated territories of Bryansk region are presented [7]. Fig. 3. An example [7] of comparison of individual thyroid doses: calculated individual doses (D 2, mGy) VS dose estimations based on the results of 131 I measurements in thyroid gland ( D 1, mGy) among inhabitants of contaminated territories of Bryansk region. Monitoring of 137 Cs activity in whole body and development of whole body internal dose reconstruction approach among inhabitants of territories contaminated by radionuclides as a result of the Chernobyl accident (Russian Federation). Starting from the fall of 1986 year till 2001 year the massive monitoring of 137 Cs activity in whole body among inhabitants of Russian territories contaminated by radionuclides as a result of Chernobyl accident was performed [11]. The detailed description of methodology developed and equipment used are presented in [12]. The results of massive monitoring of 137 Cs activity in whole body were applied for developing of approach Values*) Thyroid absorbed doses for different age groups, mGy. (age groups, years, are related to the moment of the accident) 1-2 >2-7 >7-12 >12-17 >17 N 1075 989 7491 6440 4997 5732 MID, mGy 550 530 460 320 250 250 DA, mGy 52 43 23 15 14 13 DM, mGy 31 26 14 10 8.3 8.1 GSD 2,7 2,7 2,6 2,4 2,7 2,7 of individual whole body dose reconstruction for persons who were not monitored: it is radioecological model and individual dosimetrical questionnaires for individual dose estimations by modeling calculations [13]. The developed approach of individual whole body internal dose reconstruction is still actual for implementation in a cases of possible large scale radiations accidents. As in a case of thyroid gland irradiation, it was found that statistical distribution of individual whole body doses of internal irradiation is characterized by “long tail” in the individual dose range, which is much higher than mean and median doses [12]. Figure 4 shows an example of statistical distribution of individual whole body doses of internal irradiation among inhabitants of contaminated territories of Bryansk region. Figure 4. Statistical distribution of individual whole body doses of internal irradiation (Bryansk region). On the horizontal axis ( Di , mSv): Results of estimation of individual whole body doses of internal irradiation on the base of 137 Cs activity measurements in whole body of inhabitants of contaminated territories of Bryansk region whole body doses accumulated during 15 years after the Chernobyl accident (total number of monitored persons 34 834); Results of estimation of individual whole body doses of internal irradiation on the base of developed approach of dose reconstruction (radioecological model and individual dosimetrical questionnaires) whole body doses accumulated during 15 years after the Chernobyl accident (total number of questioned persons – 1 456); On the vertical axis n,%: Percentage from total number of persons with available results of 137 Cs measurements (total number of these persons – 34 834) Percentage from total number of persons with available individual questionnaires (total number of these persons – 1 456) Figures 5 and 6 shows an examples of comparison of individual whole body doses of internal irradiation: calculated individual doses VS dose estimations based on the results of 137 Cs measurements in whole body among inhabitants of contaminated territories of Bryansk region are presented. Comparisons were performed for the same persons, which have data of 137 Cs measurements and data of individual questioning as well. Figure 5 – 1 st year after the accident (D2 = (1.24±0.25)×D1 + 1.7±2.1; R=0.98, р<0.01). Figure 6 – 15th year after the accident (D2= (1.02±0.15)×D1 + 0.12±0.41; R=0.94, р<0.01). 0 50 100 150 200 250 0 50 100 150 200 D1 D2