Distribution characteristics of natural radionuclides at some spa districts in Japan

Abstract In Japan, there are many high-level natural radiation areas such as Masutomi spa (Yamanashi pref.), Misasa spa (Tottori pref.), Ikeda spa (Shimane pref.), and Tamagawa spa (Akita pref.), etc. The Uranium and thorium decay series and K-40 are widely distributed as the sources of terrestrial radiation. Their concentrations are influenced by geological features and are nonuniform. We carried out a study of the behavior and distribution of natural radionuclides in the surrounding soils of high-level natural radiation spa areas by γ-ray energy spectrometry using a Ge(INT) diode detector. It was found that the Pb-212(Th)/Pb-214(U) ratios fluctuated widely in the same areas, of which Tamagawa spa and Masutomi spa were typical.