Further study of two-filter method for determining radon-222

The paper presents the results of further study of two-filter method for determining 222Rn. A general formula for calculating 222Rn concentration and an accurate expression for disintegration-diffusion correction coefficient Zf were derived from the basic equation for determining 222Rn daughters with filter method and by considering both disintegration and diffusion of 222Rn daughters during travel time in the sampling tube. The diffusion coefficient of RaA atoms, being 0.071 cm2/s, was determined using two-filter wall deposition method. The error propagation in two-filter method was also studiesd and it was found that the influence of uncertainty of diffusion coefficient D and sampling flow rate q on the result of determination of 222Rn decreases significantly with the decrease of the parameter μ (μ = 0.06 πDL/q, where L is the length of sampling tube). This explained theoretically why the precision and accuracy of two-filter method are so high when used in low μ value