Optimizing calibration factors of plastic scintillation fibers for improved accuracy of in situ radiocesium concentration measurements in bottom sediments of agricultural ponds

Abstract

The uncertainty of in situ radioactivity measurements can be influenced by the depth of sediment sampled by the spectrometer and the vertical distribution of the target radionuclide in the sediments. This study used Particle and Heavy Ion Transport Simulation code (PHITS) to evaluate the effective detection depth of a plastic scintillation fiber system (PSF) for monitoring radiocesium (RCs) in bottom sediments of agricultural ponds in Fukushima and thereafter, used 2015–2019 field measurement data from 47 ponds to evaluate the depth dependence of PSF calibration factors and its influence on measurement uncertainty. Though no significant differences were observed in PSF-derived RCs concentrations by calibration depth, PSF calibration factors and normalized mean square error (NMSE) suggest a potential dependence on the depth of sediment containing 90% of RCs inventory (L₉₀) such that it may be the optimal choice for calibrating PSF. Accordingly, revision of PSF calibration depth from the currently adopted top 10 cm to the top 15–20 cm may be necessary for optimizing PSF measurement uncertainty not only because their calibration factors had the best coefficients of determination and yielded lowest NMSE, but also because they constituted the largest proportion of L₉₀ among the 206 samples.

Keywords:

• Plastic scintillation fiber
• in situ radiocesium measurement
• effective detection depth
• calibration factor
• depth dependence

REVIEWING EDITOR:

• Ai Qingsong, Senior Editor, Wuhan University of Technology, China

SUBJECTS:

• Science
• Environment & Agriculture
• Agriculture & Environmental Sciences
• Environmental Sciences
• Environmental Studies & Management
• Environmental Issues
• Physical Sciences
• Physics
• Applied Physics

Acknowledgments

Japan Atomic Energy Agency and Midori Net Fukushima are gratefully acknowledged for assistance with field measurements and laboratory analyses.

Disclosure statement

Authors report that there are no competing interests to declare.

Additional information

Funding

This work was partly supported by research grants (Y-20-22 and Y-21-23) from Environmental Radioactivity Research Network Center.

Notes on contributors

Estiner W. Katengeza

Estiner W. Katengeza holds a PhD in Environmental Studies obtained from The University of Tokyo in 2022. She is a Lecturer at the Malawi University of Business and Applied Sciences’ Department of Physics and Biochemical Sciences with specializations in Physics (Applied Nuclear Physics, Energy, Environmental Sciences). Her research interests include environmental radioactivity, radiation measurement and protection, and energy. Her current research work includes natural background radiation and radon concentration measurements.

Yukihisa Sanada

Yukihisa Sanada is a Senior Principal Engineer at the Japan Atomic Energy Agency’s Sector of Fukushima Research and Development in Fukushima, Japan. He obtained a PhD in Science from Niigata University in 2006. His research interests include radiation measurement and environmental radioactivity. His work after the Fukushima Daiichi NPP accident has focused on remote radiation surveys including airborne radiation monitoring, autonomous unmanned helicopters, and developing a new type of detector for visualizing radiation distribution in forests.

Kotaro Ochi

Kotaro Ochi is a Research Engineer at the Japan Atomic Energy Agency’s Sector of Fukushima Research and Development in Fukushima, Japan. He obtained a PhD in Environmental Studies from The University of Tokyo in 2023. His research interests also include radiation measurement and environmental radioactivity. His research since 2016 has been on radiocesium inventory assessments in terrestrial soils and water bodies. Currently, he is working on research and development of remote measurement techniques using drones equipped with radiation detectors.

Takeshi Iimoto

Takeshi Iimoto is a Professor in the Division of Environmental Studies at The University of Tokyo’s Graduate School of Frontier Sciences. He graduated with a PhD from Waseda University in 1996. His laboratory’s research field is broadly classified as Environmental Safety Management and covers all studies on safety and risk management, particularly in radiation environments.