Abstract
Lithologic and geologic knowledge is essential to understand the characteristics of the distribution of terrestrial gamma ray dose rates in the Japanese Islands. However, the target fields in lithology and geology are too wide. The present paper focuses particularly on very basic theories about crystallization-differentiation of magma and partial melting of source material, which play a vital role in understanding the distribution of terrestrial gamma ray dose rates.
Soil is the main source emitting natural gamma rays which we observe outdoors. Then, it is important to know the relationship of radioactivities between rock and soil. This paper describes the transport of radioactivity from rock to soil theoretically, and evaluates reduction of dose rate due to leaching, eluviation and other effects.
Finally, this paper deals with the problem of how the terrestrial gamma ray dose rate averaged over the Japanese Islands changed from the Mesozoic up to the present. Concretely, arranging the bedrock types in order of geologic age, a historical change of dose rate levels is outlined.
