SYMPOSIA PAPER Published: 14 December 2018
STP160820170070

Gamma-Ray Imaging System for Fukushima Daiichi Nuclear Power Plant using Silicon Strip Detector

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On March 11, 2011, a massive earthquake occurred in the Tohoku region of Japan, and a large tsunami hit the Fukushima Daiichi Nuclear Power Plant (1F), resulting in a nuclear accident. Despite the years that have passed since the accident, decommissioning remains a concern. Radiation measurement techniques are very important for accelerating the decommissioning and ensuring low radiation exposure to workers. Our gamma-ray imaging system is the detection device for determining the three dimensional radioactive distributions of nuclear fuel debris, measuring high-energy gamma rays (greater than 1 MeV). Silicon semiconductor detectors are among the candidate detectors for radiation measurements in our system because of their radiation-hardness and high counting rate capability. We have been developing a stacked amorphous-silicon (Si)/crystal-Si heterojunction Si strip detector, which has 1-mm-pitch striped electrodes (0.5 mm wide) and 1.2-mm-pitch stacked technology. The detector consists of an Si strip mounted on a thin printed circuit board, front-end readout electronics with a complementary metal oxide semiconductor application-specific integrated circuit, and a field programmable gate array. The threshold level of energy deposition of each pulse signal in each channel can be set from the application-specific integrated circuit, and gamma-ray images with energy discrimination can be obtained. The energy threshold level for discrimination of 60Co gamma rays from 137Cs gamma rays was investigated experimentally and by means of simulation, and it was found to be about 500 keV. Therefore, our Si strip detector has the required position sensitivity and energy discrimination ability for identifying high-energy gamma-ray source distributions.

Author Information

Kaburagi, Masaaki
Collaborative Laboratories for Advanced Decommissioning Science, Japan Atomic Energy Agency, Fukushima, JP
Sato, Yuki
Collaborative Laboratories for Advanced Decommissioning Science, Japan Atomic Energy Agency, Fukushima, JP
Yoshihara, Yuri
Dept. of Nuclear Engineering and Management, The University of Tokyo, Tokyo, JP
Shimazoe, Kenji
Dept. of Nuclear Engineering and Management, The University of Tokyo, Tokyo, JP
Takahashi, Hiroyuki
Dept. of Nuclear Engineering and Management, The University of Tokyo, Tokyo, JP
Torii, Tatsuo
Collaborative Laboratories for Advanced Decommissioning Science, Japan Atomic Energy Agency, Fukushima, JP
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Developed by Committee: E10
Pages: 405–414
DOI: 10.1520/STP160820170070
ISBN-EB: 978-0-8031-7662-1
ISBN-13: 978-0-8031-7661-4