Measurement of Soil Concentration Profile of Radon-222 and Its Effect on Exposure Rate

The concentration profiles of ²²²Rn in the soil air are measured at several selected sites in different parts of Japan, together with the ²²⁶Ra concentrations in soil, ²²²Rn escape-to-production ratios of soil and the characteristic physical properties of the soil. The resulting data are used to derive the vertical soil concentration profile of ²²²Rn, which is found to differ distinctly from site to site. Measurements are also made of the concentrations in soil of ²³²Th and ⁴⁰K.

Based on these data, the exposure rates due to the nuclides in the soil are calculated for a level 1m above ground at each site. The lowering of exposure rate due to the diffusion loss of ²²²Rn is estimated to be 2~13% of the total exposure rate due to naturally occurring radionuclides in the soil.