Seasonal and diurnal variations of radon/thoron exhalation rate in Kanto-loam area in Japan |
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Authors: | G Prasad T Ishikawa M Hosoda A Sorimachi S K Sahoo N Kavasi S Tokonami M Sugino S Uchida |
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Institution: | (1) Research Center for Radiation Protection, National Institute of Radiological Sciences, 4-9-1 Anagawa, Inage-ku, Chiba-shi Chiba, 263-8555, Japan;(2) Hirosaki University, 66-1 Hon-cho, Hirosaki-shi Aomori, 036-8564, Japan;(3) Gunma Prefectural College of Health Sciences, 323-1 Kamioki-cho, Maebashi-shi Gunma, 371-0052, Japan; |
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Abstract: | Radon and thoron concentration in the outdoor environment are affected by the magnitude of the exhalation rate that can vary
diurnally and seasonally. This paper presents measurement results of radon and thoron exhalation rates and gamma-ray dose
rate in different season at same location points in Gunma Prefecture Japan. Exhalation rates were measured by the MSZ instrument
which is based on the accumulation method. Three measurement points Katashina Village, Midori City and Takasaki City were
selected for measurement. Soil water saturation and soil temperature were measured to investigate their relationship with
exhalation rate. The diurnal variation of exhalation rate may be correlated with soil temperature but no clear relationship
was found between them. The gamma-ray dose rate do not vary significantly at the same places even in different season. The
average radon exhalation rates were 11 ± 2, 2 ± 1, 5 ± 3 and 11 ± 4 mBq m−2 s−1 for spring, summer, autumn and winter, respectively. Those for thoron were 1,100 ± 100, 120 ± 30, 250 ± 80 and 860 ± 140 mBq m−2 s−1. Thus there was a variation of radon and thoron exhalation rate with different seasons. The radon and thoron exhalation rates
in the summer and autumn surveys are higher than those in the spring and winter surveys which were affected by rainfall. It
indicates that water saturation is an influential factor for radon and thoron exhalation rates. |
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