Underwater measurements

For underwater in-situ measurement of radiations, radiation measurement instruments are required to be designed as water and pressure resistant. In addition to the development of underwater radiation measurement system taking into account the operating environment, operation techniques of underwater equipment such as towed γ-ray spectrometer are essential to get two dimensional mapping of radiation distribution in sediment of bottom of sea or water. In this paper, in-situ radiation measurement techniques, used from the 1960s to the present for geophysics studies, marine sediment transport studies, marine mineral exploration, and anthropogenic radionuclide survey, are reviewed. Recent techniques for mapping of distribution of radionuclides in seafloor or water bottom deployed to measurement of radionuclides released from the accident at Fukushima Daiichi Nuclear Power Plant, Tokyo Electric Power Company, are also described. (author)