Monte Carlo simulation of radon emanation from dry building materials.

Prediction of radon release from building materials is a general problem. Since it is impractical to follow each recoil radon path and measure the surface area of porous texture by experimental methods, a powerful computer simulation approach is conducted in this paper. The Monte Carlo simulation program TRIM, based on the momentum and energy conservation of the ion transport in matter, is modified to simulate the recoil path in a 3-D frame. A follow-up Monte Carlo program was established further to calculate the detailed recoil range distribution and the recoil probability (emanating power). The powerful Turning Bands Method (TBM) of random field is applied to simulate the 3-D porous texture based on the porosity and the correlation function of the porous texture. Based on the simulated porous texture, the fractal dimension of the surface is calculated and used to calculate the effective surface area for radon recoil. The relations between the air buffer thickness, embedding effect of recoil, and the measuring scale of the surface area for the porous texture are discussed and numerically calculated. After these calculations are performed, the relations between the emanating rate, surface area, material density, and porosity are established to calculate the radon emanation rate from porous materials. This paper provides a clear theoretical picture of the mechanism of radon release from the building materials. It has also potential application to the recoil release calculations of other radioactive elements from solid materials.