Development of a modular high-sensitivity high-uniformity gamma camera for radiation monitoring applications

摘要

One direct way to improve the gamma camera's sensitivity is using large-area gamma detectors. During construction of a large-area gamma camera, achieving high uniformity (including both spatial uniformity and events count map uniformity) across the entire active area is a major challenge. Another fabrication concern is that large-scale gamma sensors (mainly with reference to scintillators) and photoelectric converters such as position-sensitive photomultiplier tubes (PSPMTs) and silicon photomultipliers (SiPMs) are required. In this work, to design a large-area gamma camera with high uniformity, a 22×22 CsI(Na) array with a pitch size of 4.6×4.6 mm~2 is divided into four optically isolated 11×11 modules, where each module is coupled independently to an 8×8 SiPM array (6.13×6.13 mm~2 per channel) and is then read out using separate preamplifier electronics. The preamplified signals for each module are sampled independently via their respective analog-to-digital converters (ADCs) and the digitized signals are then processed in a single field-programmable gate array (FPGA). Extra dead zones and optical losses are avoided between the modules as a result of the optimal design used in the junction area for the four modules. This modular concept leads to a high counting rate capability. 2D flood field images of the 22×22 CsI(Na) array are obtained under uniform irradiation using ~(241)Am. The counting rate measurements are performed using ~(137)Cs under various attenuation conditions. The sensitivity is tested and compared with existing devices. The results show that high uniformity (1.43) and high counting rate capability (～72% improvement) are achieved. Thanks to the large-area gamma sensor, the gamma camera developed in this paper achieves highest sensitivity among the listed devices (Locating ~(137)Cs producing 0.6±0.02 μSv/h in ＜ 10 s). The principles developed in this paper can be applied to the construction of large-area radiation detectors.