Abstract: The PMT-based LaBr₃:Ce gamma spectrometer has higher energy resolution than NaI gamma spectrometer, but it has the disadvantages such as large volume, sensitive to magnetic field and high voltage demand. Silicon photomultiplier tube (SiPM) has similar gain and efficiency as PMT, while offering excellent characteristics such as high timing resolution, high magnetic field resistance, low bias and compact size. In this paper, the LaBr₃:Ce crystal is coupled with the SiPM array, and the compact LaBr₃:Ce γ spectrometer based on SiPM is designed and developed to improve the impact of the shortcomings of SiPM on the performance of gamma spectrometer by reducing noise, optimizing the operating voltage.The noise of working voltage will lead to the deterioration of energy resolution. By designing the CLC-type π filter with passive filter circuit, the high frequency ripple can be filtered by using its different characteristics of DC/AC impedance and the signal-to-noise ratio of working voltage can be increased from 62.6 dB to 74.64 dB before the noise reduction. The minimum energy resolution corresponds to the optimum operating voltage representing a compromise between dark noise, crosstalk, photodetection efficiency, and SiPM gain. The energy resolution at different working voltages is given by experiment, and the optimal working voltage is determined to be 54.8 V. The energy resolution at this voltage is 3.06% (@662 keV), the result of which is very close to 2.89% measured by photomultiplier tube (PMT).

Key words: gamma spectrometer, LaBr₃:Ce crystal, SiPM