EVALUATION OF RADON EMANATION FROM SOIL WITH VARYING MOISTURE-CONTENTIN A SOIL CHAMBER

The EPA chamber (2 x 2 x 4 m long) was constructed to study convective and diffusive soil gas movement under known conditions of Ra-226 and Rn-222 concentration, moisture, density, soil constituent, and physica l response to pressure variation. The radon emanation rates of soil ar e known to depend strongly on the moisture content of the soil. Becaus e the moisture content varies greatly with depth in the EPA's soil cha mber (from saturated at the bottom to nearly dry at the top), it is no t possible to fully understand the radon distribution within the chamb er without knowing the emanation rate as a function of moisture. Soil radon concentrations vary in the chamber from 7.4 kBq m(-3), near the soil surface, to 86.2 kBq m(-3), at the chamber bottom. This paper des cribes measurements of the emanation coefficient and diffusion of rado n in soil contained in the chamber, using a wide range of moisture con tents. In addition, equal amounts of well-mixed oven-dried soil were p laced in 20 L aluminized gas-sampling bags, and, after approximately 1 month of in-growth, radon samples were taken, after which water was a dded, and another period of in-growth and sampling followed. The emana tion coefficients and radon concentrations in the gas bag experiment w ere observed to increase with increasing moisture content and then dec rease before reaching saturated conditions. The emanation and diffusio n effects on the radon concentration soil gradient were identified for this sandy soil having approximately 200 Bq kg(-1) radium and a soil density of 1682 kg m(-3). Copyright (C) 1996 Elsevier Science Ltd.