Decay of Reactivity in Forsterite Due to UV Radiation

The lifetime of reactive sites on the surfaces of irradiated lunar dust grains is of interest to anyone studying human health effects because of the free radicals and toxic compounds that may be formed and may not passivate quickly when exposed to habitat/spacecraft air. One of the major activators of lunar regolith grains may be ultraviolet (UV) radiation, but the contribution of UV radiation to space weathering appears to have been neglected, to our knowledge. The work reported here describes the novel use of time-resolved Raman spectroscopy to measure changes in reactivity caused by UV irradiation. The change in the dominant Raman spectrum peak centers of San Carlos olivine versus time was measured to determine the rate of decay of polished samples exposed to UV radiation in various levels of ambient humidity. The decay time of the reactivity was observed to decrease as the relative humidity increased from 0% to 100%. The chemical reactivity caused by UV exposure appears to passivate after approximately 50 minutes in air containing 45% or higher relative humidity at approximately 25 °C. Experiments such as these will provide guidance in the design and fabrication of living facilities on the Moon.