Sea bottom gamma ray measurement by NaI(Tl) scintillation spectrometers installed on manned submersibles, ROV and sea bottom long term observatory

In situ sea bottom gamma ray has been measured using manned submersibles "Shinkai2000", "Shinkai6500" and the Dolphin-3K rover. The "real-time long-term deep-sea floor observatory" with gamma ray sensor is under final test before installation on the bottom of Sagami Bay, in depth about 1200 meters. These systems utilize NaI(Tl) scintillation spectrometers of 3 inch in diameter. Three systems that are equipped on manned and unmanned submersibles are operational and a great number of measurements have been carried out around the Japanese islands, North Pacific Ocean, Mid-Atlantic Ridge, Southwest Indian Ocean and Hawaii island. The paper describes the specifications of four systems, the purpose and example of results of measurements.