Background: With large differences in mass density

Basalt

KREEP and Dunite are representative and widely distributed on lunar surface. Cosmic-induced ?-ray is produced after energetic particles (Galactic Cosmic Rays

GCR; Solar Particle Event

SPE) impacting on lunabase rocks. Purpose: This study aims at discovering the factors of cosmic-induced ?-ray spectrum and then utilizing the gamma ray data for lunar exploration more efficiency. Methods: A Monte Carlo model for proton-induced gamma ray is designed for the FLUKA simulation software to research cosmic-induced gamma original spectrum. Data analysis is applied to find the relationship between the characteristic spectrum and the densities of lunabase rocks. Results: The model is appropriate to simulate cosmic-induced ?-ray original spectrum. A great variety of original spectrum characteristics

such as energies of main elements

positron annihilation peak and radiation balanced peak

are acquired. Conclusion: A positive correlation is found between mass density of lunabase rock and characteristic peak intensity. These researches for original spectrum can be applied to comparing different lunar gamma-ray spectrum and rock mass density mapping on lunar surface as a reference. Abstract