On-ground calibration of low gain response for Gamma-Ray Detectors onboard the GECAM satellite

The Gravitational wave high-energy Electromagnetic Counterpart All-sky Monitor (GECAM) consists of two small satellites operating in the same Earth orbit with opposite phases. Its scientific goal is to monitor the electromagnetic counterparts associated with Gravitational Wave events (GWE) and other cosmic high energy transient sources. As the main detector, the Gamma-Ray Detector (GRD) adopts LaBr _3 :Ce scintillator coupled with SiPM array. Each GRD has two output channels, i.e. high gain channel (8 ∼ 250 keV) and low gain channel (50 ∼ 6000 keV). In this paper, we present the low gain calibration results of GRDs with radioactive sources on ground, including the E-C relation, energy resolution, absolute detection efficiency and spatial response. Meanwhile, the consistency between the measurements and Geant4 simulation demonstrates the accuracy of the simulation code.