Cosmic ray interactions with lunar materials: Nature and composition of species formed

The solar and galactic cosmic rays interact directly with lunar surface materials, and the dominant nature of interactions is essentially the complete absorption of corpuscles. These corpuscles damage the lattice structure, and induce a complex set of reactions in the materials producing various species. The cosmic ray damage of the lattice would not produce an amorphous layer, similar to that produced by the solar wind, because the solar wind erosion rate is faster than the cosmic ray-induced amorphous layer formation rate. The species formation rate considered in this paper are those produced by protons, the dominant component of cosmic rays. Protons produce H, H₂, OH, H₂O, and hydrogenated species of carbon, nitrogen, sulfur, etc. These species, while migrating in the material, encounter oncoming cosmic ray corpuscles, and undergo a complex set of reactions. Although a variety of species are produced by protons, the dominant contributor to the atmosphere is H₂. The H₂ flux (molecules cm^–2 sec^–1) is about 1.5 × 10⁵ as compared to the H flux of 8.4 × 10¹ and the H₂O flux of 4.6 × 10^–2. These fluxes are about 10^–3 smaller than the fluxes of the same species produced by the solar wind protons. Thus the contributions of the cosmic ray-induced species to the atmosphere is very small compared to the solar wind-induced species. Although simulated experiments showed high concentractions of OH and H₂O in the terrestrial materials of lunar type, these species concentrations in the lunar materials under the lunar environment is much smaller than those observed in the simulated experiments.