Neutron-Gamma Techniques for Planetary Exploration

Chemical analysis of planetary surfaces is necessary for the understanding of the origin and evolutionary processes of the solar system. Orbital lunar geochemical experiments performed during the Apollo 15 and 16 demonstrated that even with a low neutron flux (fast and thermal), reliable results could be extracted. We are presently studing the possibility of using a compact 14 MeV neutron generator for geochemical analysis of planetary surfaces, comets and astroids. This method allows the determination of bulk chemical composition, even in the presence of an atmosphere. This would be possible on the surface of Venus, for example, where alternate methods such as sample return are impractical. It will be possible to determine the abundances of the rock forming elements as well as some minor and trace elements, e.g. H, C, Mn, Ti, and Ni. In addition, this method can be used for continuous monitoring of elemental abundanes from a roving vehicle, for example, on the surface of Mars. Excellent capture gamma-ray spectra have been produced using 252Cf as a neutron source for environmental studies, as a preliminary investigation related to future planetary exploration. Environmental samples analyzed include suspended and bottom sediments from the Rappahannock River in Virginia.