Decay of Activity Induced by Solar Wind Implantation of Lunar Mineral Analogs

In returning humans to the Moon, we must address many problems faced by the original Apollo astronauts. Major among these is control of the fine dust (<20 µm) that makes up ~20 wt% portion of the lunar surface. This ubiquitous, clinging, sharp, abrasive, glassy dust caused a plethora of problems with seals, abrasion, and coatings, in addition to possible health problems, including "lunar dust hay-fever."

The lifetime of reactive sites on the surfaces of irradiated lunar dust grains is of interest to those studying human health because of the free radicals and toxic compounds that may be formed and may not passivate quickly when exposed to habitat/spacecraft air. Using plasma source ion implantation (PSII), we irradiated a suite of flat, polished lunar analog minerals, including olivine, orthopyroxene, clinopyroxene, plagioclase, ilmenite, pyrrhotite, chromite and glass made from lunar simulant JSC-1. The fluences used were 10^-16/cm² 4keV 4He, 10^-14/cm² 3 keV 3He and 10^-17/cm² 1 keV H, implanted in this order to avoid knock-on broadening of the lower-energy implantations. These fluences were selected to approximate the saturation of solar wind volatiles in the lunar regolith.

Raman spectroscopy was used to monitor the decay of reactive sites caused by the implanted species. The peaks in Raman spectra were very sensitive to the chemical environment. Irradiation not only caused the Raman peaks to shift, but caused peak broadening. This effect was particularly pronounced in olivine where half-lives of the reactivity in air were measured to be 104.5 min ± 16.4 for the Raman peak at 825 cm^-1 and 100.9 min ± 17.5 for the peak at 856.7 cm^-1. Peak broadening of approximately 1 cm^-1 was seen for both peaks. These preliminary experiments are being followed with granular minerals and lunar dust simulants.