Radon Concentrations and their Controlling Factors in Mud-built Houses in Dong Van Plateau Karst Geopark, Ha Giang Province

Abstract

Abstract: This article presents results of radon (222Rn) and thoron (220Rn) concentrations in room air measured inside mud-built houses that are traditional dwellings on the Dong Van Karst Plateau. The measurements were conducted in December 2016 and July 2017, corresponding to “cold” and “warm” months, respectively, by using a portable RAD7 detector. Our results show that 222Rn and 220Rn concentrations were elevated during the “warm” month and the concentrations of 220Rn were always higher than the respective 222Rn values at the same measured locations during the two months. The relatively long half-life of 222Rn (3.83 days) causes efficient dispersion and loss from room air due to air ventilation. In contrast, the much shorter half-life of 220Rn (55.6 seconds) results in elevated radiation near mud surfaces prior to attenuation into room air further away from walls and floors. Average concentrations of 220Rn in room air during both “cold” and “warm” months are much higher than in normal outside air (~10 Bq m-3). The severely elevated concentrations of 220Rn in room air of mud-built homes are likely harmful to human occupants, especially to those sleeping near mud-walls.