Albedo Protons and Neutrons Emitted from Hydrated Layers of Lunar Regolith

In 2009, NASA launched the Lunar Reconnaissance Orbiter mission to Earth's moon carrying several instruments including the Cosmic Ray Telescope for the Effects of Radiation (CRaTER). CRaTER measures Linear Energy Transfer spectra of charged particles in the lunar radiation environment, which consists of incident galactic cosmic rays, incident solar energetic particles, and albedo particles from the lunar surface. Measurements of albedo protons show an increase in proton fluxes when observing the lunar limb rather than the nadir direction. The albedo proton flux also exhibits diurnal variations, and several other anomalies in proton yields. To better understand these unexpected phenomena, the angular yields of the albedo neutrons and protons emitted from different hydrogenated layer thicknesses, due to incident galactic cosmic rays, are modeled using the MCNP Monte Carlo transport code. Establishing the presence of a hydrogen layer might also aid in developing maps of the lunar surface regions with increased water content.