Energy response of GECAM gamma-ray detector based on LaBr3:Ce and SiPM array

The Gravitational wave high-energy Electromagnetic Counterpart All-sky Monitor (GECAM) , composed of two small satellites, is a new mission to monitor the Gamma-Ray Bursts (GRBs) coincident with Gravitational Wave (GW) events with a FOV of 100% all-sky. Each GECAM satellite detects and localizes GRBs using 25 compact and novel Gamma-Ray Detectors (GRDs) in 6 keV–5 MeV. Each GRD module is comprised of LaBr₃:Ce scintillator, SiPM array and preamplifier. A large dynamic range of GRD is achieved by the high gain and low gain channels of the preamplifier. The energy response of GRD prototype was evaluated using radioactive sources in the range of 5.9–1332.5 keV. A energy resolution of 5.3% at 662 keV was determined from the ¹³⁷Cs pulse height spectra, which meets the GECAM requirement ($<$ 8% at 662 keV). Energy to channel conversion was evaluated and a nonlinearity correction was performed to reduce the residuals ($<$ 1.5%). Also, a Geant4-based simulated in-flight background and a measured GRD LaBr₃:Ce intrinsic activity were used to evaluate the capability of in-flight calibration. These results demonstrate the design of GRD.