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

Abstract

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 241Am. The counting rate measurements are performed using 137Cs 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 137Cs producing 0.6±0.02μSv/h in < 10 s). The principles developed in this paper can be applied to the construction of large-area radiation detectors.