²²²Rn escape-to-production ratio of soil is estimated based on the ²²⁶Ra concentration determined by using NaI(Tl) detector and the ²²²Rn emanating power of soil (the ²²²Rn emanating power of soil is the activity of ²²²Rn that escapes into soil gas per gram of dry soil at equilibrium state). The value for it is 32.2±5.9% for the soil of the campus of Nagoya University. The dependence of ²²²Rn escape-to-production ratio of this soil on the water content of soil is observed.
The measurement of the ²²²Rn escape-to-production ratio is also carried out by using Ge(Li) detector. In measuring the sampled soils, they are not dried because of the dependence of ²²²Rn escape-to-production ratio of the soil on the water content of soil. The measured value for the soil of the campus of Nagoya University is 38.9±5.0% and agrees with that measured by the above-mentioned technique.
In contrast to the method hitherto used, the method presented in this work enables us to evaluate exposure rate from the sources of ²³⁸U-series precisely and easily in a laboratory.