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

Experiments on ion implantation were performed in order to study the r elease mechanisms of solar particles from lunar soil grains. Helium, n eon, and argon ions were implanted into olivine and ilmenite. The rele ase temperatures of noble gases were investigated by heating samples s tepwise; the results show that they depend on irradiation energy and d ose. We conclude that the release temperature is related to the size o f bubbles in which noble gases are trapped: Noble gases in small and l arge bubbles are released at 400-600-degrees-C and 800-1200-degrees-C, respectively. In Ne and Ar implantation experiments into olivine, a c omponent was released during recrystallization of amorphized surfaces. Based on these experimental results, we suggest that components relea sed from lunar ilmenite grains at different temperatures would corresp ond 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 lu nar ilmenite grains, while they should be lost from olivine grains.