방사성 오염의 정량화 및 고속 삼차원 영상화를 위한 대면적 콤프턴 카메라의 개발

Abstract

The Compton camera, with its unique Compton kinematics-based electronic collimation method, has been extensively studied for various applications including contamination imaging in nuclear facilities, detection of special nuclear materials, and medical/molecular imaging. However, there remain several problems limiting the application area of the Compton camera — insufficient imaging sensitivity, lack of three-dimensional imaging performances, and especially absence of methodology for quantification of radioactivity. To address the limitations, this study developed the Large-Area Compton Camera (LACC) and proposed a novel methodology to estimate radioactivity of contaminations. Large monolithic NaI(Tl) scintillation detector modules were developed for the component detectors of the LACC, considering their cost-effectiveness and satisfactory performance. The performance of the developed detector modules was evaluated, showing that the energy and timing resolutions are 7.2% (for 662 keV gamma-ray) and 9.6 ns FWHM, respectively, which are comparable to those of commercial three-inch cylindrical NaI(Tl) scintillation detectors. In addition, the spatial resolution was nearly 2–8 mm FWHM for a wide energy range (59.5–1173 keV) and various interaction positions (from center to edge). The imaging performance of the LACC was experimentally evaluated for various source locations and energies. In these experimental conditions, the LACC clearly localized the location of the contaminations, even for multiple hot-spots contamination cases. Especially, the experiments for internal contamination showed the applicability of the LACC to hot-spot contamination monitoring in a concrete wall or a radioactive waste drum. The obtained imaging resolution was ~13° FWHM in real-time and ~7° FWHM after post-processing. The absolute imaging sensitivity was 7.18×10-5 for a 137Cs source at 1 m distance in front of the LACC. The activity estimation methodology was also proposed and implemented to the LACC. The activities of contamination were estimated within a few tens of percent error with the proposed methodology, not only for single point contamination but also for multiple hot-spot contamination. Overall, the results of the present study served to demonstrate the great potential of the LACC in terms of three-dimensional fast imaging. Furthermore, the proposed methodology for quantification of radioactivity would be readily implemented to future Compton imaging systems based upon the findings of this work.