The radiation measurement for seafloor sedimentary cores was carried out by using the Imaging Plate (IP) . The precise natural radiography was obtained with 48 hours (exposure time) in a shield box. Layered structures of seafloor sediments that have relatively low radioactivity like biogenic matters could be detected by autoradiography, and it was possible to identify optically unclear layers of sediments with differences of radiation characteristics. The detection limit of thickness of suspended particle layers like volcanic ashes might be sub millimeters. It was possible to identify the pinpoint position where radioactive mineral emitted α-rays at the surface of sample. Identification of pinpoint position could be possible suppose radioactive minerals that emits α-ray exposed at the surface of sample. Distribution of dose (PSL value of IP) was related to CT value (X-ray CT), which indicates dose of sedimentary core have relationships with density and atomic number of sediments. The natural radiography for seafloor sediments cores by using the Imaging Plate is considered to be a powerful new tool as a non-destructive core analysis.
Air absorbed dose rate data taken at 17 sites have been analyzed in order to understand the characteristics of dose rate levels in basaltic terrains. The dose rate increased with increase of K2O content of rock with high correlation coefficient. The contents of uranium, thorium and potassium in source materials of basaltic magma could be evaluated by fitting a model of equilibrium batch melting to the observed result. A semi-empirical formula expressing the dose rate as a function of K2O content was derived based on the above model.