73. Preliminary Survey on Radon and Thoron Concentrations in Korea

Shinji Tokonami, Masahide Furukawa and Woon Hyuk Chung^*
(^*Dept. of Physics, Pusan National Univ., Korea)

Keywords: radon, thoron, survey, dose assessment

A preliminary survey was conducted to determine atmospheric radon and thoron concentrations, and soil gas radon concentrations in South Korea. Over a one-year period, atmospheric radon and thoron measurements were made with a radon-thoron discriminative monitor, while soil gas radon measurements were made with a handmade radon monitor. The six measurement sites in the present survey were Pusan, Daegu, Daejon, Gongju, Iksan and Seoul. A polycarbonate film and a CR-39 detector were used as detectors for the radon-thoron discriminative monitor and the soil gas radon monitor, respectively. The detectors were replaced every 2-3 months during the survey period so as to observe seasonal variations of the concentration.

Table 6 summarizes the annual mean indoor and outdoor radon concentrations at each site. In terms of the radon concentration indoors and outdoors, the relative standard deviations derived from the counting data were estimated to be around 10-20%. The houses in Gongju and Daegu have mud walls and the others concrete or bricks. High indoor radon concentrations in Gongju may arise from the lack of ventilation in the living room because at one house one person stayed at home during the night only. In the case of Daejon, furthermore, the radon level might be enhanced because there are many radon hot springs around the measurement site. The outdoor radon concentration appears to be somewhat higher than the typical value of 10 Bq/m³ mentioned in the UNSCEAR report. The mean outdoor to indoor concentration ratio (O/I ratio) is estimated to be 0.6. Relatively high thoron levels were observed in some areas. There is little variation on the indoor and outdoor thoron concentrations throughout the survey period at all the sites. The thoron levels fall in the range of 10 to 90 Bq m^-3. This finding suggests that attention must be paid to existence of thoron for the accurate dose assessment. The soil gas radon concentration was observed in the range of 3.9-23.1 kBq m³. In particular, a remarkably high soil gas radon concentration was found in Daegu. In spite of the high soil radon gas, the radon concentrations indoors and outdoors are lower than expected. Since the radon concentration seems to be related not only to geological aspects or meteorological conditions, but also to geographical features at the site, further investigation is needed.

Publications:
Chung, W.H., Tokonami, S. and Furukawa, M.: Radiat. Prot. Dosim., 80, 423-426, 1998.