Pei-Yi Feng

As a new member (denoted as GECAM-D) of the Gravitational Wave Electromagnetic Counterpart All-sky Monitor (GECAM) constellation, the Gamma-ray Transient Monitor (GTM) on the DRO-A satellite is primarily designed to detect gamma-ray transients from 15 keV to 1 MeV, such as Gamma-Ray Bursts (GRBs), the high energy counterparts of Gravitational Waves (GWs) and Fast Radio Bursts (FRBs), and Soft Gamma-ray Repeaters (SGRs). DRO/GTM can also monitor the solar activities and environmental radiation of the DRO orbit. Although the SiPM-based gamma-ray detector has been successfully employed in GECAM, the issue of SiPM dark noise caused by irradiation needs further improvement. For DRO/GTM, a novel coincidence readout is proposed and implemented for the SiPM-based detector, which reduces dark noise by several orders of magnitude. This paper primarily introduces the design and ground test results.

This study aims to provide an accurate estimation of the intrinsic resolution of LaBr₃(Ce) crystal through a combination of experimental and simulation methods. We re-analyzed the data from previous Wide-Angle Compton Coincidence (WACC) and Hard X-ray Calibration Facility (HXCF) experiments, conducted PMT Single-Photoelectron Calibration (SPEC) and radial non-uniformity (also called Spot Scanning, SS) experiments to acquire new data, and combined these results with Geant4 simulations to isolate the contribution of each physical process to the total energy resolution, thereby allowing for a precise estimation of the scintillator's intrinsic resolution. For 100 keV X-rays, the total energy resolution of LaBr₃(Ce) crystal is 3.99%± 0.04% (expressed as 1-σ), with statistical fluctuations and intrinsic resolution as the main components, contributing 2.47%± 0.00% and 3.06%± 0.06%, respectively. We identify two main sources of intrinsic resolution: one primarily due to non-proportional scintillation, contributing 2.28%± 0.00%, and the other due to fluctuations in the energy transfer process, contributing 2.04%± 0.08%. We quantified six components of the total energy resolution and reconstructed the photon response using Geant4. The consistency between the reconstructed relative light yield and the experimental measurements validated the mass model of the LaBr₃(Ce) detector used in the simulations.

The GECAM series of satellites utilize LaBr3(Ce), LaBr3(Ce,Sr), and NaI(Tl) crystals as sensitive materials for gamma-ray detectors (GRDs). To investigate the non-linearity in the detection of low-energy gamma rays and address errors in the E-C relationship calibration, comprehensive tests and comparative studies of the non-linearity of these three crystals were conducted using Compton electrons, radioactive sources, and mono-energetic X-rays. The non-linearity test results for Compton electrons and X-rays displayed substantial differences, with all three crystals showing higher non-linearity for X-rays and gamma-rays than for Compton electrons. Despite LaBr3(Ce) and LaBr3(Ce,Sr) crystals having higher absolute light yields, they exhibited a noticeable non-linear decrease in light yield, especially at energies below 400 keV. The NaI(Tl) crystal demonstrated excess light output in the 6~200 keV range, reaching a maximum excess of 9.2% at 30 keV in X-ray testing and up to 15.5% at 14 keV during Compton electron testing, indicating a significant advantage in the detection of low-energy gamma rays. Furthermore, this paper explores the underlying causes of the observed non-linearity in these crystals. This study not only elucidates the detector responses of GECAM, but also marks the inaugural comprehensive investigation into the non-linearity of domestically produced lanthanum bromide and sodium iodide crystals.