Abstract
We carried out a gamma-ray spectra survey to discuss the relation between geological structures associated with discharge of hot springs and gamma-ray intensities for three radioactive elements, 40K, 214Bi and 208Tl, using a portable multi-channel gamma-ray spectrometer, in the Futsukaichi Hot spring area, Fukuoka Prefecture, Southwest Japan. A data analysis method, based on Covell's method (1959), including the error estimation of observed data was used in this study. Detection limits of gamma-ray from each element based on Currie's method (1966) was also applied.
Results of the field survey showed high gamma-ray intensity areas for Bi well correspond to inferred faults which are associated with discharge of hot springs. This means that 222Ra, the parent element of Bi, comes up to the surface together with circulating hot water. High intensity areas for Tl correspond to places of hot spring wells. This fact was interpreted that Tl is accumulated at the place where the hot water comes up to the surface rapidy, because 220Rn, the parent element of Tl, has very short half-life time. We concluded that the high gamma-ray intensities of Bi and Tl are an indicators for existence of upward-moving hot water flow.
