Calibration and Simulation Analysis of the Medium-energy Proton Detector on Chang’E-7

The bidirectional Medium-Energy Proton Detector onboard the lunar surface exploration subsystem of the Chang’E-7 lander represents the first-ever implementation of dual-direction medium-energy proton measurements on the Moon. It is capable of providing spectral data of upward- and downward-directed medium-energy protons in the range of 0.03～30 MeV, offering crucial support for modeling the lunar particle radiation environment and for radiation protection in future crewed lunar missions. The unique challenges of ground calibration for the Medium-Energy Proton Detector were addressed in this study. An electron accelerator was employed to achieve proton-equivalent energy calibration, while the full energy range was validated by analyzing the deposited energy of penetrating high-energy protons. In addition, the suppression capability against electron contamination was quantitatively evaluated through a combined approach of accelerator experiments and numerical simulations. The results show that the detector’s energy calibration deviation is better than 3%, its electron-rejection efficiency exceeds 94% for energies at or below 1.4 MeV, and the average geometric factors of the upward-and downward-facing detectors are 0.053 cm^–2·sr^–1 and 0.3041 cm^–2·sr^–1, respectively. These calibration results provide a reliable foundation for in-orbit data inversion. Furthermore, the established calibration and simulation framework offers valuable reference for the future calibration of lunar and deep-space charged-particle detectors.