Waterproof Underwater Gamma-ray Detector

In-situ environmental radiation detection underwater is important to monitor the suspect radioactivity changes in the ocean. In this study, we developed a waterproof system of a commercial gamma-ray detector (Ortec 905-4 scintillation detector). Using three radioactive point sources (Ba-133, Cs-137, and Co-60), we tested its waterproofness and radiation detectability in a water tank. The detector was housed in a waterproof casing made of 9 mm thick aluminum alloy, which was sealed with O-rings to ensure water-tightness. The casing was designed to protect the gamma-ray sensor and devices of power supply and data communication and to expose the radiation sensor's scintillator to water. The waterproof underwater gamma-ray detector was tested both on land and in a water tank at a depth of 1 m. We confirmed 24 hours waterproofness and the distinct peaks on underwater spectra corresponding to spectra measured on land (air spectra). Compared to the air spectra, the underwater gamma-ray spectra were attenuated by water.