Neutron production in lunar habitats - Paper 132
Lunar habitats constructed of either local materials or conventional materials used for spacecraft (such as aluminum) will provide protection for astronauts from solar energetic particles (SEP) and galactic cosmic rays (GCR). Although there are essentially no neutrons in the primary GCR and SEP fields, neutrons are produced by interactions of those fields with the lunar surface and with the lunar habitat. In a habitat, the neutrons can be divided into two categories: albedo neutrons moving generally upward through the habitat, and a generally downward flux created by interactions in the habitat walls. These two neutron fields differ in their energy spectrum, and as a result different mitigation strategies may be needed for different areas of the habitat in order to reduce the dose from neutrons. In this work, we calculate the 'upward' and 'downward' neutron fluences, using a variety of shielding materials and thicknesses. We also investigate the effect of other materials inside the habitat on the neutron fluences. The preliminary transport model calculations performed here verify the effectiveness of a hydrogenous shielding wall material, polyethylene, in reducing the neutron dose inside a simple lunar habitat geometry when compared to walls made of lunar regolith and aluminum. Separate transport model calculations were done for the albedo neutron spectrum rising up from the lunar soil and for GCR particles incident upon the habitat shielding. In the case of GCR ions incident on the habitat, shielding wall made of polyethylene reduced the neutron effective dose by a factor of three, compared to the other two shielding materials. (authors)