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Evaluation of Source Identification Method Based on Energy-Weighting Level with Portal Monitoring System Using Plastic Scintillator

방사선방어학회지 2020년 45권 2호 p.117 ~ 129
이현철, Koo Bon-Tack, 최창일, 박창수, 권정완, 김홍석, 정희준, 민철희,
소속 상세정보
이현철 ( Lee Hyun-Cheol ) - Yonsei University Department of Radiation Convergence Engineering
 ( Koo Bon-Tack ) - Yonsei University Department of Radiation Convergence Engineering
최창일 ( Choi Chang-Il ) - Korea Institute of Nuclear Safety
박창수 ( Park Chang-Su ) - Korea Institute of Nuclear Safety
권정완 ( Kwon Jeong-Wan ) - Korea Institute of Nuclear Safety
김홍석 ( Kim Hong-Suk ) - Korea Institute of Nuclear Safety
정희준 ( Chung Hee-Jun ) - Korea Institute of Nuclear Safety
민철희 ( Min Chul-Hee ) - Yonsei University Department of Radiation Convergence Engineering

Abstract


Background: Radiation portal monitors (RPMs) involving plastic scintillators installed at the border inspection sites can detect illicit trafficking of radioactive sources in cargo containers within seconds. However, RPMs may generate false alarms because of the naturally occurring radioactive materials. To manage these false alarms, we previously suggested an energy-weighted algorithm that emphasizes the Compton-edge area as an outstanding peak. This study intends to evaluate the identification of radioactive sources using an improved energy-weighted algorithm.

Materials and Methods: The algorithm was modified by increasing the energy weighting factor, and different peak combinations of the energy-weighted spectra were tested for source identification. A commercialized RPM system was used to measure the energy-weighted spectra. The RPM comprised two large plastic scintillators with dimensions of 174 × 29 × 7 ㎤ facing each other at a distance of 4.6 m. In addition, the in-house-fabricated signal processing boards were connected to collect the signal converted into a spectrum. Further, the spectra from eight radioactive sources, including special nuclear materials (SNMs), which were set in motion using a linear motion system (LMS) and a cargo truck, were estimated to identify the source identification rate.

Results and Discussion: Each energy-weighted spectrum exhibited a specific peak location, although high statistical fluctuation errors could be observed in the spectrum with the increasing source speed. In particular, 137Cs and 60Co in motion were identified completely (100%) at speeds of 5 and 10 km/hr. Further, SNMs, which trigger the RPM alarm, were identified approximately 80% of the time at both the aforementioned speeds.

Conclusion: Using the modified energy-weighted algorithm, several characteristics of the energy weighted spectra could be observed when the used sources were in motion and when the geometric efficiency was low. In particular, the discrimination between 60Co and 40K, which triggers false alarms at the primary inspection sites, can be improved using the proposed algorithm.

키워드

Energy-Weighted Algorithm; Plastic Scintillator; RPM System; Peak Detection; Source Identification

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