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Natural radiation levels in Fu'an city in Fujian Province of China
International Congress Series 1276 (2005) 311 – 312
www.ics-elsevier.com
Natural radiation levels in Fu’an city in Fujian Province of China Y. Luoa, W. Zhuob,*, M. Weia, S. Tokonamib, W. Wanga, Y. Yamadab, J. Chena, M. Chena a
Fujian Centre for Prevention and Control of Occupational Diseases and Chemical Poisoning, P.R. China b Radon Research Group, National Institute of Radiological Sciences, Chiba 263-8555, Japan
Abstract. A survey of natural radiation levels was performed in an area with the highest mortality of lung cancer in Fujian Province of China. Even though relatively high terrestrial gamma radiation was observed, the concentrations of indoor 222Rn, 220Rn and its progeny are near the same as the provincial averages. Annual arithmetic mean concentrations of indoor 222Rn, 220Rn and its progeny were 29, 184 and 0.8 Bq m 3, respectively. The public exposure to radon and thoron is estimated to be 1.2 mSv year 1, similar to the world average. D 2004 Elsevier B.V. All rights reserved. Keywords: Radon; Thoron; Equilibrium-equivalent thoron concentration; Gamma dose rate
1. Introduction Fu’an city populated with about 600,000 people locates in the eastern part of Fujian Province in China. Based on the Cancer Registry of Fujian Province, although the total cancer mortality in Fu’an city was not high, the mortality of lung cancer was the highest in the past decades. The reason is still unknown so far. On the other hand, very high content of 232 Th in soil was reported in the area [1], it is expected that high thoron might exist in the area. In this study, a survey of the natural radiation levels was carried out, their results are reported. 2. Materials and methods Indoor 222Rn and 220Rn were measured by the passive integrating 222Rn and 220Rn discriminative monitor [2]. The monitors were set at about 10 cm from a wall in a bedroom. The equilibrium-equivalent thoron concentration was estimated from measuring the deposition rate of its progeny [3]. The deposition rate monitors were set in the middle * Corresponding author. Tel.: +81 43 206 3111; fax: +81 43 206 4098. E-mail address: [email protected] (W. Zhuo). 0531-5131/ D 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.ics.2004.09.048
312
Y. Luo et al. / International Congress Series 1276 (2005) 311–312
Table 1 Results of indoor Period
2002.11–2003.05 2003.06–2003.12
222
Rn,
220
Rn and its progeny concentrations (Bq m 3) in Fu’an city of Fujian Province, China
Rn-222
Rn-220
Equilibrium-equivalent thoron
Mean*FS.D.
Range
MeanFS.D.
Range
MeanFS.D.
Range
33F25 24F19
4–151 4–92
182F290 186F326
ND**–1589 ND–1678
0.85F0.77 0.72F0.67
0.12–4.26 0.12–3.83
* Refers to arithmetic mean. ** Refers to lower than detection limit.
of the same room. Indoor and outdoor gamma radiation levels were measured by a NaI(Tl) scintillation radiation meter at 1 m above the ground. Indoor 222Rn, 220Rn and its progeny were measured from Nov. 2002 to Dec. 2003 in 6month intervals. A total of 100 rooms were randomly selected from 10 villages. One set of the 222Rn, 220Rn and the deposition rate monitors was used in each room. 3. Results and discussion Indoor 222Rn, 220Rn and equilibrium-equivalent of thoron concentrations measured in the 100 rooms are summarized in Table 1. The annual arithmetic mean concentrations of indoor 222Rn, 220Rn and equilibrium-equivalent thoron are 29, 184 and 0.8 Bq m 3, respectively. They are nearly the same as the averages of the whole province [4]. The mean 222 Rn concentration in the second period was about 73% of that in the first period. However, both 220Rn and equilibrium-equivalent thoron concentrations were nearly the same in the two periods. It is considered as the different ventilation rates of the rooms in the two periods. The second survey performed in the summer and autumn, the ventilation rate is expected to be higher than that of the first survey covered the winter and spring. While the decay constant of 220Rn is much larger than the ventilation rate, the change of ventilation does not affect 220Rn concentrations. Indoor and outdoor gamma dose rates are averaged to be 184F26 and 188F26 nGy h 1 in the 100 rooms. 220Rn was detected out in about 90% of the rooms. The abundant indoor 220 Rn and the high gamma dose rate are considered as the high content of 232Th in the soil [1]. Based on the results from this survey and another study [4], public exposure to radon and thoron in Fu’an city are estimated to be 0.90 and 0.32 mSv year 1 by using the conversion factors provided by the UNSCEAR report [5]. The total exposure to radon and thoron is about 1.2 mSv year 1. It is nearly the same as the world average [5]. Public exposure to radon and thoron in Fu’an city is not significant. Other studies are still needed to explore reasons of high mortality rate of lung cancer in the area. References [1] J. Chen, et al., Radionuclide contents in soil and their contribution to public dose in Fujian, Chin. J. Radiol. Med. Prot. 8 (Suppl. 2) (1988) 60 – 66 (in Chinese). [2] W. Zhuo, et al., A simple passive monitor for integrating measurements of indoor thoron concentrations, Rev. Sci. Instrum. 73 (2002) 2881 – 2887. [3] W. Zhuo, T. Iida, Estimation of thoron progeny concentrations in dwellings with their deposition rate measurements, Jpn. J. Health Phys. 35 (2000) 365 – 370. [4] W. Zhuo, T. Iida, X. Yang, Environmental radon and thoron progeny concentrations in Fujian Province of China, Radiat. Prot. Dosim. 87 (2000) 137 – 140. [5] UNSCEAR, Sources and Effects of Ionizing Radiation, New York, United Nations, 2000.
www.ics-elsevier.com
Natural radiation levels in Fu’an city in Fujian Province of China Y. Luoa, W. Zhuob,*, M. Weia, S. Tokonamib, W. Wanga, Y. Yamadab, J. Chena, M. Chena a
Fujian Centre for Prevention and Control of Occupational Diseases and Chemical Poisoning, P.R. China b Radon Research Group, National Institute of Radiological Sciences, Chiba 263-8555, Japan
Abstract. A survey of natural radiation levels was performed in an area with the highest mortality of lung cancer in Fujian Province of China. Even though relatively high terrestrial gamma radiation was observed, the concentrations of indoor 222Rn, 220Rn and its progeny are near the same as the provincial averages. Annual arithmetic mean concentrations of indoor 222Rn, 220Rn and its progeny were 29, 184 and 0.8 Bq m 3, respectively. The public exposure to radon and thoron is estimated to be 1.2 mSv year 1, similar to the world average. D 2004 Elsevier B.V. All rights reserved. Keywords: Radon; Thoron; Equilibrium-equivalent thoron concentration; Gamma dose rate
1. Introduction Fu’an city populated with about 600,000 people locates in the eastern part of Fujian Province in China. Based on the Cancer Registry of Fujian Province, although the total cancer mortality in Fu’an city was not high, the mortality of lung cancer was the highest in the past decades. The reason is still unknown so far. On the other hand, very high content of 232 Th in soil was reported in the area [1], it is expected that high thoron might exist in the area. In this study, a survey of the natural radiation levels was carried out, their results are reported. 2. Materials and methods Indoor 222Rn and 220Rn were measured by the passive integrating 222Rn and 220Rn discriminative monitor [2]. The monitors were set at about 10 cm from a wall in a bedroom. The equilibrium-equivalent thoron concentration was estimated from measuring the deposition rate of its progeny [3]. The deposition rate monitors were set in the middle * Corresponding author. Tel.: +81 43 206 3111; fax: +81 43 206 4098. E-mail address: [email protected] (W. Zhuo). 0531-5131/ D 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.ics.2004.09.048
312
Y. Luo et al. / International Congress Series 1276 (2005) 311–312
Table 1 Results of indoor Period
2002.11–2003.05 2003.06–2003.12
222
Rn,
220
Rn and its progeny concentrations (Bq m 3) in Fu’an city of Fujian Province, China
Rn-222
Rn-220
Equilibrium-equivalent thoron
Mean*FS.D.
Range
MeanFS.D.
Range
MeanFS.D.
Range
33F25 24F19
4–151 4–92
182F290 186F326
ND**–1589 ND–1678
0.85F0.77 0.72F0.67
0.12–4.26 0.12–3.83
* Refers to arithmetic mean. ** Refers to lower than detection limit.
of the same room. Indoor and outdoor gamma radiation levels were measured by a NaI(Tl) scintillation radiation meter at 1 m above the ground. Indoor 222Rn, 220Rn and its progeny were measured from Nov. 2002 to Dec. 2003 in 6month intervals. A total of 100 rooms were randomly selected from 10 villages. One set of the 222Rn, 220Rn and the deposition rate monitors was used in each room. 3. Results and discussion Indoor 222Rn, 220Rn and equilibrium-equivalent of thoron concentrations measured in the 100 rooms are summarized in Table 1. The annual arithmetic mean concentrations of indoor 222Rn, 220Rn and equilibrium-equivalent thoron are 29, 184 and 0.8 Bq m 3, respectively. They are nearly the same as the averages of the whole province [4]. The mean 222 Rn concentration in the second period was about 73% of that in the first period. However, both 220Rn and equilibrium-equivalent thoron concentrations were nearly the same in the two periods. It is considered as the different ventilation rates of the rooms in the two periods. The second survey performed in the summer and autumn, the ventilation rate is expected to be higher than that of the first survey covered the winter and spring. While the decay constant of 220Rn is much larger than the ventilation rate, the change of ventilation does not affect 220Rn concentrations. Indoor and outdoor gamma dose rates are averaged to be 184F26 and 188F26 nGy h 1 in the 100 rooms. 220Rn was detected out in about 90% of the rooms. The abundant indoor 220 Rn and the high gamma dose rate are considered as the high content of 232Th in the soil [1]. Based on the results from this survey and another study [4], public exposure to radon and thoron in Fu’an city are estimated to be 0.90 and 0.32 mSv year 1 by using the conversion factors provided by the UNSCEAR report [5]. The total exposure to radon and thoron is about 1.2 mSv year 1. It is nearly the same as the world average [5]. Public exposure to radon and thoron in Fu’an city is not significant. Other studies are still needed to explore reasons of high mortality rate of lung cancer in the area. References [1] J. Chen, et al., Radionuclide contents in soil and their contribution to public dose in Fujian, Chin. J. Radiol. Med. Prot. 8 (Suppl. 2) (1988) 60 – 66 (in Chinese). [2] W. Zhuo, et al., A simple passive monitor for integrating measurements of indoor thoron concentrations, Rev. Sci. Instrum. 73 (2002) 2881 – 2887. [3] W. Zhuo, T. Iida, Estimation of thoron progeny concentrations in dwellings with their deposition rate measurements, Jpn. J. Health Phys. 35 (2000) 365 – 370. [4] W. Zhuo, T. Iida, X. Yang, Environmental radon and thoron progeny concentrations in Fujian Province of China, Radiat. Prot. Dosim. 87 (2000) 137 – 140. [5] UNSCEAR, Sources and Effects of Ionizing Radiation, New York, United Nations, 2000.