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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 …