Solar proton activation of the lunar surface

Abstract

The nuclear activation on the surface of the moon due to solar protons has been estimated. Proton and neutron fluxes and the production rate of radionuclides have been calculated as a function of depth, and comparisons have been made between several models of the lunar crust. The purpose of the calculations has been to evaluate the effectiveness of lunar material as a radiation shield and also to predict the particle flux reflected from the surface. The build-up of Mn54, Na22, C14, and Be7 are given in compositions representing both the volcanic and meteoritic-impact hypotheses for the lunar surface. The effect of the angular distribution of the protons on the radionuclide production rate and particle fluxes has also been investigated. Examples involving a monoenergetic beam of 400-Mev protons as well as a solar proton spectrum are included, permitting direct comparisons with experimental irradiations of similar targets. The results show that the activation is strongly dependent on the spectrum and angular distribution of incident protons but relatively insensitive to the composition.