Abstract
A long-term measurement technique of radon exhalation rate was previously developed using a passive type radon and thoron discriminative monitor and a ventilated type accumulation chamber. In the present study, this technique was applied to evaluate the thoron exhalation rate as well, and long-term measurements of radon and thoron exhalation rates were conducted for four years in Gifu Prefecture. The ventilated type accumulation chamber (0.8 × 0.8 × 1.0 m3) with an open bottom was embedded 15 cm into the ground. The vertical distributions of radon and thoron activity concentrations from the ground were obtained using passive type radon-thoron discriminative monitors (RADUETs). The RADUETs were placed at 1, 3, 10, 30, and 80 cm above the ground inside the accumulation chamber. The measurements were conducted from autumn 2014 to autumn 2018. These long-term results were found to be in good agreement with the values obtained by another methodology. The radon exhalation rates from the ground showed a clearly seasonal variation. Similar to findings of previous studies, radon exhalation rates from summer to autumn were relatively higher than those from winter to spring. In contrast, thoron exhalation rates were not found to show seasonal variation.
Highlights
IntroductionRadon (222 Rn) and thoron (220 Rn) are naturally occurring radioactive gases generated from the 238 U- and 232 Th-series
Introduction published maps and institutional affilRadon (222 Rn) and thoron (220 Rn) are naturally occurring radioactive gases generated from the 238 U- and 232 Th-series
The second chamber has 6 holes of 6 mm of diameter opened at the side of the chamber which allow the diffusion of thoron as well as radon, the 6 holes are recovered by an electroconductive sponge to block the passage of charges particulate in the diffusion chamber [20]
Summary
Radon (222 Rn) and thoron (220 Rn) are naturally occurring radioactive gases generated from the 238 U- and 232 Th-series. It is well known that radon and thoron are the biggest contributors to human radiation exposure from natural sources [1]. Indoor and outdoor radon and thoron concentrations vary widely from place to place depending on geological features and meteorological condition of an area (see, e.g., [3]). Indoor radon concentration is continuously supplied by a portion of outdoor radon, an infiltration rate of 10 Bq m−3 h−1 was reported [1]. In addition to the health effect assessment due to its inhalation, outdoor radon monitoring is useful in several scientific disciplines as a radioactive tracer. Outdoor radon monitoring serves on earthquake forecasting, geological faults identifications or ore iations
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