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ESR dosimetry study for the residents of Kazakhstan exposed to radioactive fallout on 24, August 1956
Radiation Measurements 46 (2011) 793e796
Contents lists available at ScienceDirect
Radiation Measurements journal homepage: www.elsevier.com/locate/radmeas
ESR dosimetry study for the residents of Kazakhstan exposed to radioactive fallout on 24, August 1956 K. Zhumadilov a, *, A. Ivannikov b, D. Zharlyganova c, Zh. Zhumadilov d, V. Stepanenko b, Sh. Abralina e, L. Sadvokasova e, A. Zhumadilova c, S. Toyoda f, S. Endo g, T. Okamoto h, M. Hoshi a a
Research Institute for Radiation Biology and Medicine, Hiroshima University, Kasumi 1-2-3, Minami-ku, Hiroshima 734-8553, Japan Medical Radiological Research Center, Obninsk 249036, Russia Astana Medical University, 51a, Beibitshilik str., Astana 010000, Kazakhstan d Nazarbayev University, Life Sciences Center, D. Kunayev str., Astana 010000, Kazakhstan e Semey State Medical Academy, Semey 071400, Abay str. 103, Kazakhstan f Department of Applied Physics, Faculty of Science, Okayama University of Science, Okayama 700-0005, Japan g Department of Quantum Energy Applications, Graduated School of Engineering, Hiroshima University, 1-4-1 Kagamiyama, Higashi-Hiroshima 739-8527, Japan h Department of Molecular Oral Medicine and Maxillofacial Surgery, Division of Frontier Medical Science, Graduate School of Biomedical Sciences, Hiroshima University, Hiroshima 734-8553, Japan b c
a b s t r a c t Keywords: ESR dosimetry Tooth enamel Semipalatinsk nuclear test site Retrospective dosimetry
The method of electron spin resonance (ESR) dosimetry has been applied to human tooth enamel in order to obtain individual absorbed doses from the population of settlements within the vicinity of the central axis of the radioactive fallout trace from the contaminating nuclear surface test of 24, August 1956. Most of the settlements (Glubokoe, Tavriya, and Gagarino) are located near Ust-Kamenogorsk city, in Kazakhstan (about 400 km to the east from the epicenter of the explosion at the Semipalatinsk Nuclear Test Site (SNTS)). It was found that the excess doses obtained after the subtraction of natural background radiation ranged up to about 120 mGy for the residents of Ust-Kamenogorsk city, whose tooth enamel was formed before 1956. For the residents of Gagarino, excess doses do not exceed 47 mGy for all ages. For the residents of Tavriya, the maximum of excess dose was determined as 54 mGy and for the residents of Glubokoe, the maximum excess dose was about 83 mGy. For the population of the Shemonaikha settlements (about 70 km from the centerline of the radioactive fallout trace) the highest excess dose is 110 mGy. Also for this study, Znamenka village (about 130 km from the epicenter) was included. The Kokpekty settlement was chosen as a control and not subjected to any radioactive contamination and is located 400 km to the Southeast from SNTS. Crown Copyright Ó 2011 Published by Elsevier Ltd. All rights reserved.
1. Introduction The Semipalatinsk Nuclear Test Site (SNTS) is located on the territory of the East-Kazakhstan oblast, Kazakhstan. In the period from 1949 to 1962, 125 nuclear tests (including 25 near-surface nuclear tests) were conducted at the Ground Zero technical site in the territory of the SNTS. An analytical assessment of external exposure to residents living in settlements near SNTS is described in Logachev et al., (2008). This method makes use of the archival data on the radiological condition, including the measurements of the exposure rate. The purpose of this study is to compare archival data and the data of Electron spin resonance (ESR) dosimetry based
* Corresponding author. Tel.: þ81 82 257 5419; fax: þ81 82 257 5873. E-mail addresses: [email protected], [email protected] (K. Zhumadilov).
on tooth enamel measurements of the population exposed by the 28th nuclear explosion, on 24 August 1956, with 27 ktonne total yield and which contaminated a huge territory to the east of the hypocenter and near Ust-Kamenogorsk city with radioactive fallout (Gordeev et al., 2002, 2006). Ust-Kamenogorsk is the main city of the East-Kazakhstan region that was developed as a major mining and metallurgical center during the Soviet period. The mining of non-ferrous metals, especially uranium, beryllium, tantalum, copper, lead, silver and zinc, remain important. After the 2nd World War, the industrial history of the city was very closely intertwined with the Soviet Union nuclear bomb project, and the city was therefore kept classified (Zhumadilov et al., 2009). Ex-vivo ESR dosimetry is one of the tools for retrospective individual dose reconstruction (IAEA Report, 2002; Wieser et al., 2006; Simon et al., 2007; Hoshi et al., 2007; Ivannikov et al., 2007; Zhumadilov et al., 2008; Fattibene and Callens, 2010). This
1350-4487/$ e see front matter Crown Copyright Ó 2011 Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.radmeas.2011.05.005
794
K. Zhumadilov et al. / Radiation Measurements 46 (2011) 793e796
method can help to estimate the individual absorbed doses more than 50 years after the exposure event. The ESR measures the number of radicals created by ionizing radiation exposure in tooth enamel. The detection threshold of this method is relatively low, i.e. approximately 30e50 mGy in terms of an absorbed dose (Romanyukha et al., 2005).
The enamel samples for the calibration curve were prepared from molars collected as a control sample from the population of the Kokpekty village (Fig. 1). Tooth enamel powder, prepared from different teeth, was pooled together and split into aliquots of 100 mg. Each of the aliquots was successively irradiated with six doses (0,100, 200, 300, 500 and 1000 mGy) and measured (Ivannikov et al., 2010). The dose uncertainty due to the calibration source is 3%.
2. Materials and methods 2.2. ESR measurement 2.1. Sampling From 2009, a group of scientists from Kazakhstan, Japan and Russia made an additional effort to determine the individual absorbed doses of those exposed to nuclear fallout, by means of the ESR method. The studied group includes the population of UstKamenogorsk city (tooth ages from 1935 to 1994), Glubokoe (tooth ages from 1939 to 1988), Tavriya (tooth ages from 1938 to 1950), Gagarino (tooth ages from 1941 to 1951)) located in the vicinity of the radioactive fallout trace formed as result of the nuclear test in 1956, Shemonaikha (tooth ages from 1938 to 1990) which is located at a distance of about 70 km from the center of the radioactive trace (Logachev et al., 2008) and Znamenka village located at a distance of about 5 km from the radioactive fallout trace (Fig. 1). The Kokpekty settlement (located about 150 km to SouthWest of Ust-Kamenogorsk city) was chosen as a control and not subjected to any radioactive contamination (Table 1). In 2010, 29 tooth samples were additionally investigated from adult residents of Ust-Kamenogorsk city, as well as the Glubokoe and the Shemonaikha settlements. In total, 88 tooth samples have been studied. The buccal part was not included in the dose estimation procedure because their position within the oral cavity did not exclude the possibility of sun light exposure which could affect the ESR signal (IAEA, 2002, Sholom et al., 2010). Eight teeth have been measured from the population of Kokpekty village (tooth ages from 1960 to 1995). According to information obtained by questionnaires, none of the tooth donors were subjected to any X-ray procedure of the jaw. Each tooth samples was cut to its buccal and lingual parts. The enamel was mechanically separated from dentine using hard alloy dental drills and diamond saws (IAEA, 2002; Zhumadilov et al., 2005). The enamel samples were crushed by cutting pliers to chips 0.5e1.5 mm grid.
The ESR measurements were carried out at least ten days after irradiation and sample preparation, so that all transient radiation and mechanical-induced signals had faded out or had come to an equilibrium state (IAEA, 2002). All measurements were performed at a stabilized room temperature of 21 C using an X-band ESR spectrometer JEOL JES-FA100, equipped with a high Q-factor cylindrical TE011 cavity model ES-UCX2, and keeping the spectrum recording parameters similar as previously published (Ivannikov et al., 2006; Zhumadilov et al., 2007). Specially designed computer software (Ivannikov et al., 2001, 2002b) was used for the spectra processing. The parameters of the calibration curve applied for a radiation signal of up to 1 Gy the dose responses of the EPR signal and was evaluated under linear approximation, and the radiation sensitivity of enamel (as a radiation detector) was calculated by the averaging of regression slopes normalized by the samples mass and by the amplitude of the marker signal. The fitting procedure was performed in the automatic mode of the processing program. The average theoretical expectation for the background doses (estimated according to Ivannikov et al., 2002a) corresponded to the ages and positions of the control teeth was used as a correction term (24 mGy) instead of value corresponded to the average intercept evaluated from regression. The excess dose in enamel was determined by the subtraction of the natural background radiation accumulated after enamel formation from the absorbed dose in the enamel. The natural background dose is 0.8 mGy/y (Ivannikov et al., 2002a). The corresponding uncertainty of dose determination was determined based on a semi-empirical formula used in Ivannikov et al., (2006); Zhumadilov et al., 2007. The lifetime of the tooth enamel was obtained by the subtraction of the average age of tooth formation for a given tooth position
Fig. 1. Centerline of the radioactive fallout trace after the 24, August 1956 nuclear explosion conducted at the Semipalatinsk Nuclear Test Site (SNTS); the circled area marks the region of investigation.
K. Zhumadilov et al. / Radiation Measurements 46 (2011) 793e796
795
Table 1 Population in the investigated settlements in 2007 with distance of the axis of radioactive fallout trace from nuclear test on 24, August 1956, archival data of external dose estimations (Logachev et al., 2008), and results of the present study. Settlements
Distance from the axis, km
Znamenka Glubokoe Tavriya Ust-Kamenogorsk Gagarino Shemonaikha Kokpekty
5 20 15 10 3 70 130
Population
11,192 4280 298,700 1038 17,000 5301
Number of teeth
Number of anterior
Number of posterior
Archival dose (mSv) (Logachev)
ESR average excess dose (mGy)
9 14 10 30 10 15 8
3 1 4 6 5 2 e
6 13 6 24 5 13 8
25 10e15 10e15 80 10e15 0.1 <0.1
70 30 20 20 20 30 0.01
from the age of a person at the moment of measurement. The age of tooth enamel formation was determined according data from previous publication (IAEA, 2002; Fattibene and Callens, 2010).
3. Results and discussion The absorbed doses with their uncertainties were obtained as result of the spectra processing as described above. In order to minimize the effects of any unknown X-ray diagnostic contribution to a dose, only the results obtained for the lingual part have been used for further analysis. For the residents of Ust-Kamenogorsk absorbed doses range from 0 10 to 190 10 mGy, for Glubokoe from 10 20 to 140 10 mGy, for Tavriya from 10 20 to 130 20 mGy, for Shemonaikha from 20 10 to 150 20 mGy, and for Gagarino from 0 20 to 120 20 mGy, respectively. For the minimal dose of UstKamenogorsk city residents, negative values were obtained, because the measurements were performed near the threshold of sensitivity of this method. This value is probably the result of the underestimation of uncertainty of the dose assessment and appeared in the course of mathematical processing. It must not be rejected as having no physical meaning and should be used for statistical treatment to get unbiased average values. For the Tavriya and Gagarino villages, the enamel of the teeth studied was developed before the date of the nuclear test. For other settlements tooth samples were divided into two groups: those developed before and after the nuclear test. Low mean excess doses have been found for Gagarino residents, while the highest mean excess dose has been determined for Shemonaikha and UstKamenogorsk residents (Table 1). Given the small number of tooth samples investigated, the deduced doses should not be seen as representative for the whole population in the selected villages. The maximum dose obtained for the samples from Shemonaikha was not expected due to its large distance from the radioactive trace, while possibly due to exposure from radioactivity releases from local uranium enterprises, seems equally likely from undocumented occupational or medical exposures. The maximum dose obtained for Znamenka village (Ivannikov et al., 2002a) can confirm that this village is located close to the radioactive trace. The other settlements included in the study also have uranium enterprises, except for Tavriya and Gagarino, where agriculture is prevalent. Average excess doses in the latter two settlements are consistent with estimations based on the official registered data indicating high levels of fallout in the period 1949e1962 (Logachev et al., 2008). The difference between background doses and doses in the investigated population has been tested for statistical significance by student t-test (GraphPad software). P value equals 0.03. By conventional criteria, this difference is considered to be statistically significant. For the difference between the mean ESR dose and theoretical dose in Logachev et al., (2008) P value equals 0.84 and this difference is considered to be not statistically significant.
60 30 40 30 30 30 1.92
ESR maximal excess dose (mGy) 268 (Ivannikov et al., 2002a) 83 54 (Zhumadilov et al., 2009) 120 47 (Zhumadilov et al., 2009) 110 24 (Zhumadilov et al. 2007)
4. Conclusions Individual absorbed doses have been determined for the residents of different settlements affected by the fallout trace of nuclear test in 24 August 1956. Compared to samples from the distant Kokpekty village which were chosen as controls, higher average excess doses have been obtained for Znamenka. This is in agreement with the fact that Znamenka village is located close to the axis of the radioactive trace. For other settlements, the average ESR excess doses are very close to background level of exposure and they are not in contradiction to the theoretical estimation by Logachev et al., (2008). Acknowledgement The present study was supported by Grant-in-Aid for Young Scientists (B) from Japan Society for the Promotion of Science #21710060. References Fattibene, P., Callens, F., 2010. EPR dosimetry with tooth enamel: a review. Appl. Radiat. Isot. 68, 2033e2116. Gordeev, K., Vasilenko, I., Lebedev, A., Bouville, A., Luckyanov, N., Simon, S.L., Stepanov, Y., Shinkarev, S., Anspaugh, L., 2002. Fallout from nuclear tests: dosimetry in Kazakhstan. Radiat. Environ. Biophys. 41, 61e67. Gordeev, K., Shinkarev, S., Ilyin, L., Bouville, A., Hoshi, M., Luckyanov, N., Simon, S.L., 2006. Retrospective dose assessment for the population living in areas of local fallout from the Semipalatinsk nuclear test site Part I: external exposure. J. Radiat. Res. 47, A129eA136. Hoshi, M., Toyoda, S., Ivannikov, A., Zhumadilov, K., Fukumura, A., Apsalikov, K., Zhumadilov, Z.S., Bayankin, S., Chumak, V., Ciesielski, B., De Coste, V., Endo, S., Fattibene, P., Ivanov, D., Mitchell, C.A., Onori, S., Penkowski, M., Pivovarov, S.P., Romanyukha, A., Rukhin, A.B., Schultka, K., Seredavina, T.A., Sholom, S., Skvortsov, V., Stepanenko, V., Tanaka, K., Trompier, F., Wieser, A., Wolakiewicz, G., 2007. Interlaboratory comparison of tooth enamel dosimetry on Semipalatinsk region: Part 1, general view. Radiat. Meas. 42, 1005e1014. IAEA Report, 2002. Use of Electron Paramagnetic Resonance Dosimetry with Tooth Enamel for Retrospective Dose Assessment Report of a coordinated research project. IAEA-TECDOC-1331. Vienna. Ivannikov, A.I., Skvortsov, V.G., Stepanenko, V.F., Tikunov, D.D., Takada, J., Hoshi, M., 2001. EPR tooth enamel dosimetry: optimization of the automatic spectra deconvolution procedure. Health Phys. 81, 124e137. Ivannikov, A.I., Zhumadilov, Zh., Gusev, B.I., Miyazawa, Ch., Jiao, L., Skvortsov, V.G., Stepanenko, V.F., Takada, J., Hoshi, M., 2002a. Individual dose reconstruction among residents living in the vicinity of the Semipalatinsk Nuclear Test Site using EPR spectroscopy of tooth enamel. Health Phys. 83, 183e196. Ivannikov, A.I., Trompier, F., Gaillard-Lecanu, E., Skvortsov, V.G., Stepanenko, V.F., 2002b. Optimization of recording conditions for the electron paramagnetic resonance signal used in dental enamel dosimetry. Radiat. Prot. Dosim. 100, 531e538. Ivannikov, A., Zhumadilov, K., Tieliewuhan, E., Jiao, L., Zharlyganova, D., Apsalikov, K.N., Berekenova, G., Zhumadilov, Zh., Toyoda, Sh., Miyazawa, C., Skvortsov, V., Stepanenko, V., Endo, S., Tanaka, K., Hoshi, M., 2006. Results of EPR dosimetry for population in the vicinity of the most contaminating radioactive fallout trace after the first nuclear test in the Semipalatinsk Test Site. J. Radiat. Res. 47, A39eA46. Ivannikov, A., Toyoda, S., Hoshi, M., Zhumadilov, K., Fukumura, A., Apsalikov, K., Zhumadilov, Z.S., Bayankin, S., Chumak, V., Ciesielski, B., De Coste, V., Endo, S., Fattibene, P., Ivanov, D., Mitchell, C.A., Nalapko, M., Onori, S., Penkowski, M., Pivovarov, S.P., Romanyukha, A., Rukhin, A.B., Sanin, D., Schultka, K.,
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Seredavina, T., Sholom, S., Skvortsov, V., Stepanenko, V., Tanaka, K., Trompier, F., Wieser, A., Wolakiewicz, G., 2007. Interlaboratory comparison of tooth enamel dosimetry on Semipalatinsk region: Part 2, effects of spectrum processing. Radiat. Meas. 42, 1015e1020. Ivannikov, A.I., Sanin, D., Nalapko, M., Skvortsov, V.G., Stepanenko, V.F., Tsyb, A.F., Trompier, F., Zhumadilov, K., Hoshi, M., 2010. Dental enamel EPR dosimetry: comparative testing of the spectra processing methods for determination of radiation induced-signal amplitude. Health Phys. 98, 345e351. Logachev, V.A., et al., 2008. Nuclear Tests in the USSR and their Influence on the Health of the Population of the Russian Federation M., IzdAT, 470. Romanyukha, A.A., Schauer, D.A., Thomas, J.A., Regulla, D.F., 2005. Parameters affecting EPR dose reconstruction in teeth. Appl. Radiat. Isot. 62, 147e154. Simon, S.L., Bailiff, I., Bouville, A., Fattibene, P., Kleinerman, R.A., Lloyd, D.C., McKeever, S.W.S., Romanyukha, A., Sevan’kaev, A.V., Tucker, J.D., Wieser, A., 2007. BiodosEPR-2006 consensus committee report on biodosimetric methods to evaluate radiation doses at long times after exposure. Radiat. Meas. 42, 948e971. Sholom, S., Desrosiers, M., Chumak, V., Luckyanov, N., Simon, S.L., Bouville, A., 2010. UV effect in tooth enamel and their possible application in EPR dosimetry with front teeth. Health Phys. 98, 360e368. Wieser, A., Vasilenko, E., Fattibene, P., Bayankin, S., El-Faramawy, N., Ivanov, D., Jacob, P., Knyazev, V., Onori, S., Pressello, M.C., Romanyukha, A., Smetanin, M.,
Ulanovsky, A., 2006. Comparison of EPR occupational lifetime external dose assessments for Mayak nuclear workers and film badge dose data. Radiat. Environ. Biophys. 44, 279e288. Zhumadilov, K.S., Ivannikov, A.I., Skvortsov, V.G., Zhumadilov, Zh.S., Endo, S., Tanaka, K., Hoshi, M., 2005. Tooth enamel EPR dosimetry: selecting optimal spectra registration parameters and effects of sample mass on sensitivity. J. Radiat. Res. 46, 435e442. Zhumadilov, K., Ivannikov, A., Apsalikov, K., Zhumadilov, Zh., Zharlyganova, D., Stepanenko, V., Skvortsov, V., Berekenova, G., Toyoda, S., Endo, S., Tanaka, K., Miyazawa, C., Hoshi, M., 2007. Results of tooth enamel EPR dosimetry for population living in the vicinity of the Semipalatinsk nuclear test site. Radiat. Meas. 42, 1049e1052. Zhumadilov, K., Stepanenko, V., Ivannikov, A., Zhumadilov, Z., Zharlyganova, D., Toyoda, S., Tanaka, K., Endo, S., Hoshi, M., 2008. Measurement of absorbed doses from X-ray baggage examinations to tooth enamel by means of ESR and glass dosimetry. Radiat. Environ. Biophys. 47, 541e545. Zhumadilov, K., Ivannikov, A., Zharlyganova, D., Zhumadilov, Z., Stepanenko, V., Apsalikov, K., Rodzi, M., Zhumadilova, A., Toyoda, S., Endo, S., Tanaka, K., Okamoto, T., Hoshi, M., 2009. ESR dosimetry study on population of settlements nearby Ust-Kamenogorsk city, Kazakhstan. Radiat. Environ. Biophys. 48, 419e425.
Contents lists available at ScienceDirect
Radiation Measurements journal homepage: www.elsevier.com/locate/radmeas
ESR dosimetry study for the residents of Kazakhstan exposed to radioactive fallout on 24, August 1956 K. Zhumadilov a, *, A. Ivannikov b, D. Zharlyganova c, Zh. Zhumadilov d, V. Stepanenko b, Sh. Abralina e, L. Sadvokasova e, A. Zhumadilova c, S. Toyoda f, S. Endo g, T. Okamoto h, M. Hoshi a a
Research Institute for Radiation Biology and Medicine, Hiroshima University, Kasumi 1-2-3, Minami-ku, Hiroshima 734-8553, Japan Medical Radiological Research Center, Obninsk 249036, Russia Astana Medical University, 51a, Beibitshilik str., Astana 010000, Kazakhstan d Nazarbayev University, Life Sciences Center, D. Kunayev str., Astana 010000, Kazakhstan e Semey State Medical Academy, Semey 071400, Abay str. 103, Kazakhstan f Department of Applied Physics, Faculty of Science, Okayama University of Science, Okayama 700-0005, Japan g Department of Quantum Energy Applications, Graduated School of Engineering, Hiroshima University, 1-4-1 Kagamiyama, Higashi-Hiroshima 739-8527, Japan h Department of Molecular Oral Medicine and Maxillofacial Surgery, Division of Frontier Medical Science, Graduate School of Biomedical Sciences, Hiroshima University, Hiroshima 734-8553, Japan b c
a b s t r a c t Keywords: ESR dosimetry Tooth enamel Semipalatinsk nuclear test site Retrospective dosimetry
The method of electron spin resonance (ESR) dosimetry has been applied to human tooth enamel in order to obtain individual absorbed doses from the population of settlements within the vicinity of the central axis of the radioactive fallout trace from the contaminating nuclear surface test of 24, August 1956. Most of the settlements (Glubokoe, Tavriya, and Gagarino) are located near Ust-Kamenogorsk city, in Kazakhstan (about 400 km to the east from the epicenter of the explosion at the Semipalatinsk Nuclear Test Site (SNTS)). It was found that the excess doses obtained after the subtraction of natural background radiation ranged up to about 120 mGy for the residents of Ust-Kamenogorsk city, whose tooth enamel was formed before 1956. For the residents of Gagarino, excess doses do not exceed 47 mGy for all ages. For the residents of Tavriya, the maximum of excess dose was determined as 54 mGy and for the residents of Glubokoe, the maximum excess dose was about 83 mGy. For the population of the Shemonaikha settlements (about 70 km from the centerline of the radioactive fallout trace) the highest excess dose is 110 mGy. Also for this study, Znamenka village (about 130 km from the epicenter) was included. The Kokpekty settlement was chosen as a control and not subjected to any radioactive contamination and is located 400 km to the Southeast from SNTS. Crown Copyright Ó 2011 Published by Elsevier Ltd. All rights reserved.
1. Introduction The Semipalatinsk Nuclear Test Site (SNTS) is located on the territory of the East-Kazakhstan oblast, Kazakhstan. In the period from 1949 to 1962, 125 nuclear tests (including 25 near-surface nuclear tests) were conducted at the Ground Zero technical site in the territory of the SNTS. An analytical assessment of external exposure to residents living in settlements near SNTS is described in Logachev et al., (2008). This method makes use of the archival data on the radiological condition, including the measurements of the exposure rate. The purpose of this study is to compare archival data and the data of Electron spin resonance (ESR) dosimetry based
* Corresponding author. Tel.: þ81 82 257 5419; fax: þ81 82 257 5873. E-mail addresses: [email protected], [email protected] (K. Zhumadilov).
on tooth enamel measurements of the population exposed by the 28th nuclear explosion, on 24 August 1956, with 27 ktonne total yield and which contaminated a huge territory to the east of the hypocenter and near Ust-Kamenogorsk city with radioactive fallout (Gordeev et al., 2002, 2006). Ust-Kamenogorsk is the main city of the East-Kazakhstan region that was developed as a major mining and metallurgical center during the Soviet period. The mining of non-ferrous metals, especially uranium, beryllium, tantalum, copper, lead, silver and zinc, remain important. After the 2nd World War, the industrial history of the city was very closely intertwined with the Soviet Union nuclear bomb project, and the city was therefore kept classified (Zhumadilov et al., 2009). Ex-vivo ESR dosimetry is one of the tools for retrospective individual dose reconstruction (IAEA Report, 2002; Wieser et al., 2006; Simon et al., 2007; Hoshi et al., 2007; Ivannikov et al., 2007; Zhumadilov et al., 2008; Fattibene and Callens, 2010). This
1350-4487/$ e see front matter Crown Copyright Ó 2011 Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.radmeas.2011.05.005
794
K. Zhumadilov et al. / Radiation Measurements 46 (2011) 793e796
method can help to estimate the individual absorbed doses more than 50 years after the exposure event. The ESR measures the number of radicals created by ionizing radiation exposure in tooth enamel. The detection threshold of this method is relatively low, i.e. approximately 30e50 mGy in terms of an absorbed dose (Romanyukha et al., 2005).
The enamel samples for the calibration curve were prepared from molars collected as a control sample from the population of the Kokpekty village (Fig. 1). Tooth enamel powder, prepared from different teeth, was pooled together and split into aliquots of 100 mg. Each of the aliquots was successively irradiated with six doses (0,100, 200, 300, 500 and 1000 mGy) and measured (Ivannikov et al., 2010). The dose uncertainty due to the calibration source is 3%.
2. Materials and methods 2.2. ESR measurement 2.1. Sampling From 2009, a group of scientists from Kazakhstan, Japan and Russia made an additional effort to determine the individual absorbed doses of those exposed to nuclear fallout, by means of the ESR method. The studied group includes the population of UstKamenogorsk city (tooth ages from 1935 to 1994), Glubokoe (tooth ages from 1939 to 1988), Tavriya (tooth ages from 1938 to 1950), Gagarino (tooth ages from 1941 to 1951)) located in the vicinity of the radioactive fallout trace formed as result of the nuclear test in 1956, Shemonaikha (tooth ages from 1938 to 1990) which is located at a distance of about 70 km from the center of the radioactive trace (Logachev et al., 2008) and Znamenka village located at a distance of about 5 km from the radioactive fallout trace (Fig. 1). The Kokpekty settlement (located about 150 km to SouthWest of Ust-Kamenogorsk city) was chosen as a control and not subjected to any radioactive contamination (Table 1). In 2010, 29 tooth samples were additionally investigated from adult residents of Ust-Kamenogorsk city, as well as the Glubokoe and the Shemonaikha settlements. In total, 88 tooth samples have been studied. The buccal part was not included in the dose estimation procedure because their position within the oral cavity did not exclude the possibility of sun light exposure which could affect the ESR signal (IAEA, 2002, Sholom et al., 2010). Eight teeth have been measured from the population of Kokpekty village (tooth ages from 1960 to 1995). According to information obtained by questionnaires, none of the tooth donors were subjected to any X-ray procedure of the jaw. Each tooth samples was cut to its buccal and lingual parts. The enamel was mechanically separated from dentine using hard alloy dental drills and diamond saws (IAEA, 2002; Zhumadilov et al., 2005). The enamel samples were crushed by cutting pliers to chips 0.5e1.5 mm grid.
The ESR measurements were carried out at least ten days after irradiation and sample preparation, so that all transient radiation and mechanical-induced signals had faded out or had come to an equilibrium state (IAEA, 2002). All measurements were performed at a stabilized room temperature of 21 C using an X-band ESR spectrometer JEOL JES-FA100, equipped with a high Q-factor cylindrical TE011 cavity model ES-UCX2, and keeping the spectrum recording parameters similar as previously published (Ivannikov et al., 2006; Zhumadilov et al., 2007). Specially designed computer software (Ivannikov et al., 2001, 2002b) was used for the spectra processing. The parameters of the calibration curve applied for a radiation signal of up to 1 Gy the dose responses of the EPR signal and was evaluated under linear approximation, and the radiation sensitivity of enamel (as a radiation detector) was calculated by the averaging of regression slopes normalized by the samples mass and by the amplitude of the marker signal. The fitting procedure was performed in the automatic mode of the processing program. The average theoretical expectation for the background doses (estimated according to Ivannikov et al., 2002a) corresponded to the ages and positions of the control teeth was used as a correction term (24 mGy) instead of value corresponded to the average intercept evaluated from regression. The excess dose in enamel was determined by the subtraction of the natural background radiation accumulated after enamel formation from the absorbed dose in the enamel. The natural background dose is 0.8 mGy/y (Ivannikov et al., 2002a). The corresponding uncertainty of dose determination was determined based on a semi-empirical formula used in Ivannikov et al., (2006); Zhumadilov et al., 2007. The lifetime of the tooth enamel was obtained by the subtraction of the average age of tooth formation for a given tooth position
Fig. 1. Centerline of the radioactive fallout trace after the 24, August 1956 nuclear explosion conducted at the Semipalatinsk Nuclear Test Site (SNTS); the circled area marks the region of investigation.
K. Zhumadilov et al. / Radiation Measurements 46 (2011) 793e796
795
Table 1 Population in the investigated settlements in 2007 with distance of the axis of radioactive fallout trace from nuclear test on 24, August 1956, archival data of external dose estimations (Logachev et al., 2008), and results of the present study. Settlements
Distance from the axis, km
Znamenka Glubokoe Tavriya Ust-Kamenogorsk Gagarino Shemonaikha Kokpekty
5 20 15 10 3 70 130
Population
11,192 4280 298,700 1038 17,000 5301
Number of teeth
Number of anterior
Number of posterior
Archival dose (mSv) (Logachev)
ESR average excess dose (mGy)
9 14 10 30 10 15 8
3 1 4 6 5 2 e
6 13 6 24 5 13 8
25 10e15 10e15 80 10e15 0.1 <0.1
70 30 20 20 20 30 0.01
from the age of a person at the moment of measurement. The age of tooth enamel formation was determined according data from previous publication (IAEA, 2002; Fattibene and Callens, 2010).
3. Results and discussion The absorbed doses with their uncertainties were obtained as result of the spectra processing as described above. In order to minimize the effects of any unknown X-ray diagnostic contribution to a dose, only the results obtained for the lingual part have been used for further analysis. For the residents of Ust-Kamenogorsk absorbed doses range from 0 10 to 190 10 mGy, for Glubokoe from 10 20 to 140 10 mGy, for Tavriya from 10 20 to 130 20 mGy, for Shemonaikha from 20 10 to 150 20 mGy, and for Gagarino from 0 20 to 120 20 mGy, respectively. For the minimal dose of UstKamenogorsk city residents, negative values were obtained, because the measurements were performed near the threshold of sensitivity of this method. This value is probably the result of the underestimation of uncertainty of the dose assessment and appeared in the course of mathematical processing. It must not be rejected as having no physical meaning and should be used for statistical treatment to get unbiased average values. For the Tavriya and Gagarino villages, the enamel of the teeth studied was developed before the date of the nuclear test. For other settlements tooth samples were divided into two groups: those developed before and after the nuclear test. Low mean excess doses have been found for Gagarino residents, while the highest mean excess dose has been determined for Shemonaikha and UstKamenogorsk residents (Table 1). Given the small number of tooth samples investigated, the deduced doses should not be seen as representative for the whole population in the selected villages. The maximum dose obtained for the samples from Shemonaikha was not expected due to its large distance from the radioactive trace, while possibly due to exposure from radioactivity releases from local uranium enterprises, seems equally likely from undocumented occupational or medical exposures. The maximum dose obtained for Znamenka village (Ivannikov et al., 2002a) can confirm that this village is located close to the radioactive trace. The other settlements included in the study also have uranium enterprises, except for Tavriya and Gagarino, where agriculture is prevalent. Average excess doses in the latter two settlements are consistent with estimations based on the official registered data indicating high levels of fallout in the period 1949e1962 (Logachev et al., 2008). The difference between background doses and doses in the investigated population has been tested for statistical significance by student t-test (GraphPad software). P value equals 0.03. By conventional criteria, this difference is considered to be statistically significant. For the difference between the mean ESR dose and theoretical dose in Logachev et al., (2008) P value equals 0.84 and this difference is considered to be not statistically significant.
60 30 40 30 30 30 1.92
ESR maximal excess dose (mGy) 268 (Ivannikov et al., 2002a) 83 54 (Zhumadilov et al., 2009) 120 47 (Zhumadilov et al., 2009) 110 24 (Zhumadilov et al. 2007)
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