Abstract

In extravehicular activity and in the Lunar Excursion Module, the astronaut is protected from environmental ionizing radiation merely by 0.1 to 0.2 g/cm² of material. Behind such low shielding, in addition to protons, alpha particles and heavy nuclei in solar particle beams contribute to exposure. Separate analysis of the proton, alpha, and medium heavy fluxes for the November 12, 1960 flare shows that, on the rad dose level, only the alpha component contributes significantly to total dose and does so only in the first 5 millimeters of tissue. On the RBE dose level, the alpha component is the predominant contributor in near-surface regions, becoming equal to the proton dose at 2-millimeter depth in tissue. The contribution of the medium heavy group never exceeds, even in the tissue surface and on the RBE dose level, a few per cent of total exposure. No experimental data with laboratory radiations exist that would lend themselves to an interpretation of the peculiar depth dose patterns for flare-produced particles behind low shielding in terms of radiation damage or permissible exposure.