MOISTURE-CONTENT EFFECT ON RADON EMANATION IN POROUS-MEDIA

It is impractical to establish the detailed recoil range distribution and to measure the rough recoil surface of the porous media experiment ally. Thus a computer based modelling approach is followed. The ion co llision theory of nuclear physics provides the basics for calculating the recoil range distributions for radon within solid, water and air. The collision history is established by the modified Monte Carlo TRIM program. The recoil emanation power can also be calculated from the re coil range distributions. The recoil surface areas of the porous media are calculated through the fractal quantification of the synthetic po rous media. The embedding effects are numerically calculated for solid , water and air, the three coexisting phases. The moisture distributio n in the porous media is discussed based on the capillary theory. The simulation results indicate that the radon emanation rate is positivel y correlated with the moisture saturation in the porous media. The gre ater the moisture saturation is, the greater the possible radon emanat ion rate is. With moisture contents from 10% up to 30%, the recoil ema nation rates quickly reach the emanation rate of the saturated conditi on. As the moisture reaches 30%, a universal thin film on the pore sur face is formed. This thin film is sufficient to stop the recoil radon from embedding into another part of the pore wall. The existing experi mental data support this result.