In situ measurement of Cs-134 and Cs-137 in seabed using underwater gamma-spectrometry systems: application in surveys following the Fukushima Dai-ichi Nuclear Power Plant accident

摘要

Two underwater gamma-spectrometric systems incorporating NaI(Tl) detectors (the seabed mooring system and the towing system) were used to measure radiocesium in seabed that was released due to the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident and assess the accuracy of in situ measurements on seabed. We also applied a simple calculating method for seabed radiocesium by separating the gamma-spectra based on four contributions (Cs-134 + Cs-137, K-40, U-series, and Th-series radionuclides). The concentration of Cs-134 + Cs-137 in sediments at two sites in Sendai Bay were calculated to be between 10-250 Bq/kg-dry through our method with a short integration time (1-5 min).