Gadd M S, Borak T B
Department of Radiological Health Sciences, Colorado State University, Fort Collins 80523, USA.
Health Phys. 1995 Jun;68(6):817-22. doi: 10.1097/00004032-199506000-00008.
Measurements of the effective diffusion coefficient, De, of 222Rn in concrete are important for accurate determination of transport mechanisms and computer modeling of radon entry into structures. A method for in-situ determination of De as well as the emanation fraction, F, is described. It is based on continuous measurement of the radon flux from an intact slab and the concentrations on both sides. A non-linear regression algorithm was used to fit these data to the steady state solution to Fick's law. The regression output includes estimates of both De and F. The method has the advantage over typical laboratory procedures since it measures an undisturbed surface area of concrete where the samples exhibit moisture, temperature, and loading conditions that are experienced in a real structure. Effective diffusion coefficients ranged from 1.1 x 10(-8) to 4.4 x 10(-8) m2 s-1 for measurements of concrete floor slabs in two structures. The measured emanation fraction of radon in concrete in one structure was 0.2 +/- 0.02. A sensitivity analysis indicated that the values of De and F estimated by the regression procedure are strongly dependent on the thickness of the slab. The porosity of the concrete had little affect on the regression results.
测定混凝土中222Rn的有效扩散系数De，对于准确确定传输机制以及对氡进入建筑物的计算机建模而言至关重要。本文描述了一种原位测定De以及析出率F的方法。该方法基于对完整平板的氡通量以及两侧浓度的连续测量。使用非线性回归算法将这些数据拟合到菲克定律的稳态解。回归输出包括De和F的估计值。该方法相对于典型的实验室程序具有优势，因为它测量的是混凝土未受扰动的表面积，样品在该表面呈现出真实结构中所经历的湿度、温度和荷载条件。在对两座建筑物的混凝土楼板进行测量时，有效扩散系数范围为1.1×10(-8)至4.4×10(-8) m2 s-1。在一座建筑物中测得的混凝土中氡的析出率为0.2±0.02。敏感性分析表明，通过回归程序估计的De和F值强烈依赖于平板的厚度。混凝土的孔隙率对回归结果影响很小。
