HELIUM AND NEON IN LUNAR ILMENITES OF DIFFERENT ANTIQUITIES

Helium and neon were extracted from individual lunar ilmenite grains, approximately 100 mum in diameter, using a pulsed stepheating techniqu e. Grains from lunar samples 71501 and 79035, believed to have been ex posed to solar corpuscular radiation at greatly different times, were studied. The results found were consistent with the hypothesis that in addition to solar-wind-implanted gas, a second more deeply implanted component was present in both species of grains. Average isotopic rati os were determined giving equal weight to each of the particles. As fo und in depth studies employing chemical etching, both the He-3/He-4 an d Ne-20/Ne-22 ratios were lower in the more deeply implanted gas than in the solar wind component. The He-3/He-4 ratio in the solar wind com ponent of the more ancient grains was lower than that in the more rece ntly exposed ones, whereas no difference was found for the more deeply embedded He. In the deeply embedded component of the ancient grains, the He-4/Ne-20 ratio was approximately 2x that found in the more recen tly exposed grains. In the shallowly implanted component, the ratio va ried greatly from grain to grain, preventing comparison with the solar wind elemental composition.