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Continuous measurement of radionuclide distribution off Fukushima using a towed sea-bed gamma ray spectrometer

Instrumentation and data processing methods to continuously map the distribution of radionuclides on the seafloor have been developed and applied to survey radioactive discharge from the Fukushima Dai-ichi Nuclear Power Plant following the M9.0 earthquake and tsunami that struck the east coast of Ja...

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Bibliographic Details
Published in:Deep-sea research. Part I, Oceanographic research papers Oceanographic research papers, 2013-09, Vol.79, p.10-19
Main Authors: Thornton, Blair, Ohnishi, Seiki, Ura, Tamaki, Odano, Naoteru, Fujita, Tsuneo
Format: Article
Language:English
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Summary:Instrumentation and data processing methods to continuously map the distribution of radionuclides on the seafloor have been developed and applied to survey radioactive discharge from the Fukushima Dai-ichi Nuclear Power Plant following the M9.0 earthquake and tsunami that struck the east coast of Japan on March 11 2011. The instrument consists of a flexible rubber hose with an integrated gamma ray spectrometer that measures the full gamma spectrum between 0.1 and 1.8MeV while being towed along the seafloor by a ship. The data processing methods described allow for quantification of 137Cs and 134Cs concentration in marine sediments, and a technique has been developed to optimize the spatial resolution of the measurements for each radioactive species for a given level of statistical uncertainty. The system was deployed during August and November 2012 to measure the distribution of radionuclides along three transects within an 80km radius of the plant. Increased levels of 137Cs and 134Cs were recorded and their distributions mapped continuously over distances of 1.6, 12.5 and 22km respectively. The levels of 137Cs and 134Cs were found to vary significantly with location. The in situ measurements show good agreement with laboratory analyzed samples obtained during the surveys. The results demonstrate that the instrument and data processing techniques described enable high resolution, quantitative measurements of 137Cs and 134Cs in marine sediments, and provide an effective solution for rapid, low cost monitoring of radioactive material on the seafloor. •A towed gamma ray spectrometer has been developed to survey seafloor radiation.•Methods to quantify the in situ measurements of the system are described.•An algorithm is developed to optimize spatial resolution based on uncertainty.•Continuous 137Cs and 134Cs distributions are measured along transects off Fukushima.•The accuracy of the system is verified through comparison with samples.
ISSN:0967-0637
1879-0119
DOI:10.1016/j.dsr.2013.05.001