EXPERIMENTS ON THERMAL RELEASE OF IMPLANTED NOBLE-GASES FROM MINERALS AND THEIR IMPLICATIONS FOR NOBLE-GASES IN LUNAR SOIL GRAINS

Experiments on ion implantation were performed in order to study the release mechanisms of solar particles from lunar soil grains. Helium, neon, and argon ions were implanted into olivine and ilmenite. The release temperatures of noble gases were investigated by heating samples stepwise; the results show that they depend on irradiation energy and dose. We conclude that the release temperature is related to the size of bubbles in which noble gases are trapped: Noble gases in small and large bubbles are released at 400-600-degrees-C and 800-1200-degrees-C, respectively. In Ne and Ar implantation experiments into olivine, a component was released during recrystallization of amorphized surfaces. Based on these experimental results, we suggest that components released from lunar ilmenite grains at different temperatures would correspond to solar particles of different energies. We also suggest that He and Ne of solar wind energy (about 1 keV/amu) should be retained in lunar ilmenite grains, while they should be lost from olivine grains.