抄録
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 re-sulting 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 concentra-tions 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 1 m above ground at each site. The lowering of exposure rate due to the dif-fusion loss of 222Rn is estimated to be 213% of the total exposure rate due to naturally occurring radionuclides in the soil.
