Abstract
There are approximately 3,700 irrigation ponds in Fukushima prefecture, and contamination by radiocesium in the bottom sediments of these ponds has been a concern since the accident at the TEPCO's Fukushima Daiichi Nuclear Power Station. Although three years have passed since the accident, some irrigation reservoirs contain radioactive materials in the bottom sediment, and there is therefore a concern about the migration of radioactive cesium into the environment in relation to the restoration of agriculture in the disaster-stricken area. In this study, a 20 meter-length plastic scintillation fiber (PSF) was developed to enable measurements of radioactive cesium in water. The PSF detects the radiation incident position using the differences between the detection times of the photomultiplier located at both ends of the tube. In addition, as the detection element has no mechanical structure, the PSF is designed to sink underwater. Such characteristics are effective for use in measuring the distribution of radiocesium in the bottom sediment. Tests were conducted at dozens of irrigation ponds in Fukushima prefecture to confirm the performance of the device and to standardize associated measurement techniques and analytical procedures.
