A low-energy sensitive compact gamma-ray detector based on LaBr3 and SiPM for GECAM

The Gravitational wave high-energy Electromagnetic Counterpart All-sky Monitor (GECAM) project is the planned Chinese space telescope for detecting the X- and gamma-ray. It consists of two micro-satellites in low earth orbit with the advantages of instantaneous full-sky coverage. Due to the limitation of size, weight and power consumption of micro-satellites, silicon photomultipliers (SiPMs) are used to replace the photomultiplier tubes (PMTs) to assemble a novel gamma-ray detector. A prototype of a SiPM array with LaBr₃ crystal is built and tested, and it shows a high detection efficiency (70% at 5.9 keV) and an acceptable uniformity. The low energy X-ray of 5.9 keV can be detected by single channel readout circuit, and the energy resolution are 125% (FWHM) at 5.9 keV, 6.5% at 662 keV and 3.5% at 1332 keV . The design and the performance of the detector are discussed in this paper.