Gamma-ray Dose Rates in Igneous Rock Terrains in the Japanese Islands

Abstract

Air absorbed dose rates evaluated from uranium, thorium and potassium contents in rock samples have been compared with SiO₂ and K₂O data in order to understand lithologic characteristics of terrestrial γ-ray dose rate levels in igneous rock terrains. The comparison showed that the dose rate increased with increasing SiO₂ or K₂O content of rock. The models of partial melting of rock and crystallization differentiation of magma were used to analyze this trend quantitatively. As a result, a semi-empirical formula could be derived for expressing the dose rate as a function of K₂O content of rock.