부호화 구경 기반의 휴대용 이중입자 영상장비 개발

Abstract

Dual particle imaging, in which both neutrons and gamma-rays in the environment can be individually characterized, is particularly attractive for monitoring mixed radiation emitters such as special nuclear materials (SNM). An effective SNM localization and detection benefits from high instrument sensitivity so that real-time imaging or imaging with a limited number of acquired events is enabled. For portable applications, one also desires a dual particle imager (DPI) that is readily deployable. We have developed a hand-held type DPI equipped with a pixelated stilbene-silicon photomultiplier (SiPM) array module and low sampling-rate analog-to-digital converters (ADCs) processed via a multiplexed readout. The stilbene-SiPM array (12 × 12 pixels) is capable of effectively performing pulse shape discrimination (PSD) between gamma-ray and neutron events and neutron/gamma-ray source localization on the imaging plane, as demonstrated with 252Cf neutron/gamma and 137Cs gamma-ray sources. The low sampling rate ADCs connected to the stilbene-SiPM array module result in a compact instrument with high sensitivity that provides a gamma-ray image of a 137Cs source, producing 6.4 μR/h at 1 m, in less than 69 seconds. A neutron image for a 3.5 × 105 n/s 252Cf source can also be obtained in less than 6 minutes at 1 m from the center of the system. The instrument images successfully with field of view of 50° and provides angular resolution of 6.8°. This study also illustrates a positive effect of a large light-absorption area in a photodetector, such as a SiPM array, on the PSD performance despite the use of ADCs that have a low bit resolution (12 bit) and a low sampling rate (50 MHz). To the best of our knowledge, there have been few studies on how to improve a degraded capability of discrimination between the gamma-ray and neutron pulses in DPI systems that mount a pixelated scintillator array. With improved PSD performance in the pixelated array sensor module of the DPI system, gamma-ray and neutron events can be used as much as possible for the reconstruction of gamma-ray and neutron images, respectively, enabling rapid image acquisition.