Radon exhalation behavior and determination of diffusion migration parameters in spherical porous emanation media

There is a significant impact of the radon diffusion coefficient and the free radon production rate on the exhalation of radon from porous materials that can be regarded as spheres, hexahedrons, or cylinders. To understand this effect, the radon exhalation rules of spherical porous media with different radii were studied according to the radon diffusion migration theory. A specialized method for simultaneous determination of the radon diffusion coefficient and the free radon production rate of the spherical porous media was proposed, and applied to determine the above two parameters for two hemispherical test blocks with different radii. The results show that:(1) For spherical porous media with a certain radon diffusion length (L_d), as the radius (r₀) of the sphere increases, the radon exhalation rate first increases, and tends to stabilize at r₀≥6L_d; The free radon release share gradually decreases from approximately 1, and drops to a steady state at r₀≥18L_d. (2) Compared with conventional methods, the relative error of the free radon production rate determined by the proposed method is within 3.9%, which verifies the reliability of the new method.