Soil radon gas in some soil types in the rainy season in Ho Chi Minh City, Vietnam

Field experiments on soil radon and radium concentrations were carried out in eighteen locations in Ho Chi Minh City, Vietnam. Soil radon depth profiles (10-100 cm) of loam, sand and clay soil samples in the rainy season were measured using RAD7 radon detector. Mean concentrations of 222Rn and 226Ra were found to be 28.6 ± 2.0 Bq.kg−1 and (1.56 ± 0.06) × 104 Bq.m−3 in clay soil while they are 31.2 ± 2.5 Bq.kg−1 and (1.15 ± 0.05) × 104 Bq.m−3 in loam soil. They are 30.7 ± 2.0 Bq.kg−1 and (9.37 ± 0.52) × 103 Bq.m−3 in sandy soil, respectively. Values of radon diffusion length and diffusion coefficient for different soils were obtained using semi-empirical fit method linked to the poor diffusion of gas in clay soil (0.2 × 10−6 m2 s−1), the moderate diffusion coefficient (0.9 × 10−6 m2 s−1) in loam and good diffusion of radon gas in sandy soil (1.4 × 10−6 m2 s−1). An unexpectedly unclear linear relation was found between soil radon concentration and radium content. The grain size smaller than 0.1 mm was dominant reason for the lowest (0.15 ± 0.01) and highest (0.40 ± 0.03) values emanation coefficient for sand and clay soil, respectively. A strong positive correlation was found between radon concentration and soil pH level leads to soil pH is an indirect dynamic parameter affecting the migration of radon in soil.