Gamma ray production and transport in Mars

The elemental composition of the Martian surface can be determined by gamma ray spectroscopy from landers or orbiting spacecraft. We used the well-tested Los Alamos High Energy Transport (LAHET) Code System (LCS) to numerically simulate the galactic-cosmic-ray-induced processes producing secondary particles and gamma rays in Mars. For gamma ray lines, LCS was used only for the calculation of the particle fluxes in the Martian soil and atmosphere; these fluxes were then integrated with cross sections to calculate the production rates of gamma rays as a function of depth. The fluxes of gamma ray lines were then calculated both at the Martian surface and at an altitude of 378 km. The water content of the Martian soil and the atmospheric thickness were varied to establish the dependence of the particle distributions and gamma ray fluxes on these parameters. Most attention is devoted to gamma rays from neutron-induced reactions in the Martian soil, but contributions from the atmosphere, natural radioactivity, and from proton interactions are also mentioned. Our results are compared with those from previous studies.