Experimental setup for evaluation of radon effective diffusion coefficient in soil

Full text: It has been well recognized that radon and its decay products inhalation significantly contributes to the exposure of public. Radon is mainly generated from soil, building material and ground water. The infiltration of radon gas from soil has been identified as one of the main mechanisms influencing indoor radon levels. Therefore, radon exhalation rate from soil is one of the most important factors for the evaluation of environmental radon levels. In order to estimate the radon exhalation rate, several parameters related to soil characteristic have to be determined (i.e. effective diffusion coefficient, porosity and moisture content). In this study, an optimum experimental set-up to evaluate the radon effective diffusion coefficient was examined. This experimental setup consists of radon source (radon chamber), measuring device (scintillation cell) and diffusion column. The radon chamber calibrated by PTB (Physikalisch-Technischen Bundesanstalt, Germany) was applied as the radon source system. Also the measuring device was calibrated by the same facilities. The diffusion column was filled with glass beads instead of soil. As radon does not generate from the glass beads, therefore, it was possible to evaluate the effective diffusion coefficient precisely. Considering quality assurance of this experimental set-up, preliminary experiments as checking leakage and evaluating the radon effective diffusion coefficient in gas phase were performed. And an analytical method which evaluates the effective diffusion coefficient in a short time was discussed in this study. In general, experimental method for evaluating the effective diffusion coefficient is classified in a steady state method and a transient method. The transient method can evaluate the effective diffusion coefficient in a short time, however, it is very difficult to reach the analytical solution because two independent variables (time and position) have to be treated at the same time. In this study, a suitable analytical solution for this transient method was also discussed. Using this experimental setup, influences of porosity and moisture content on the effective diffusion coefficient were evaluated. (author)