Effects of intraparticle porosity on the radon emanation coefficient

An analysis of the effects on the radon emanation from individual material particles by the direct recoil process and the intraparticle porosity is presented. The purpose is to fill the gap in knowledge for a comprehensive theoretical explanation of the nature of the radon emanation processes. The overall fractional release at the particle boundaries is mechanistically described as a diffusion process. In this model, the solid and the pore diffusion as well as the direct recoil processes are essentially working in parallel. The net generation rate of the emanation atoms within the particle domain is treated as an effective generation rate beta(eff). An analytical solution of radon release from the diffusion-based equation is derived for short and long times. By employing this analysis as a re-interpretive device for the existing experimental data, new or improved values of diffusion coefficients may be determined. The diffusion coefficient of Rn-222 for fly ash samples from various source and for different particle sizes is in the range of 1.05 x 10(-17) to 9.17 x 10(-17) cm(2) s(-1). Using the above values of D, the contributions of three components for various particle size are examined.