¹Derek W. G. Sears,¹Alexander Sehlke,²Harrison H. Schmitt, the ANGSA Science Team
Journal of Geophysical Research (Planets) Open Access Link to Article [https://doi.org/10.1029/2024JE008358]
¹NASA Ames Research Center/Bay Area Environmental Research Institute, Moffett Field, CA, USA
²Department of Engineering Physics, University of Wisconsin-Madison, Albuquerque, NM, USA
Published by arrangement with John Wiley & Sons

By placing Apollo 17 regolith samples in a freezer, and storing an equivalent set at room temperature, NASA effectively performed a 50-year experiment in the kinetics of natural thermoluminescence (TL) of the lunar regolith. We have performed a detailed analysis of the TL characteristics of four regolith samples: a sunlit sample near the landing site (70180), a sample 3 m deep near the landing site (70001), a sample partially shaded by a boulder (72320), and a sample completely shaded by a boulder (76240). We find evidence for a total of eight discrete TL peaks, five apparent in curves for samples in the natural state and seven in samples irradiated in the laboratory at room temperature. For each peak, we suggest values for peak temperatures and the kinetic parameters E (activation energy, i.e. “trap depth,” eV) and s (Arrhenius factor, s−1). The lowest natural TL peak in the continuously shaded sample 76240 dropped in intensity by 60 ± 10% (1976 vs. present room temperature samples) and 43 ± 8% (freezer vs. room temperature samples) over the 50-year storage period, while sunlit and partially shaded samples (70001, 70180, 72321, 72320) showed no change. These results are consistent with the E and s parameters we determined. The large number of peaks, and the appearance of additional peaks after irradiation at room temperature, and literature data, suggest that glow curve peaks are present in lunar regolith at ∼100 K and their intensity can be used to determine temperature and storage time. Thus, a TL instrument on the Moon could be used to prospect for micro-cold traps capable of the storage of water and other volatiles.

¹Mitsuru Ebihara, ²Naoki Shirai, ³Takahito Osawa, ⁴Akira Yamaguchi
Geochimica Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2024.10.026]
¹Department of Chemistry, Tokyo Metropolitan University, Hachioji, Tokyo 192-0397, Japan
²Department of Chemistry, Kanagawa University, Yokohama, Kanagawa 221-0802, Japan
³Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195, Japan
⁴National Institute of Polar Research, Tachikawa, Tokyo 190-8518, Japan
Copyright Elsevier

Fifteen elements, including most of the major elements, were quantified using neutron-induced prompt gamma-ray analysis for five Antarctic carbonaceous chondrites with CI affinities and seven with CM affinities. Common among the twelve meteorites is the depletion of volatile elements H and chlorine, showing a positive correlation and being depleted compared to non-Antarctic CI levels. This depletion is not thought to have occurred after the fall on Antarctica, but to have been caused by thermal metamorphism on the parent body. Among the meteorites analyzed in this study, six meteorites (Y-86029, Y 980115, Y-82162 (with CI affinities), Y-86720, Y-86789, B-7904 (with CM affinities)) have previously been proposed to constitute a new meteorite group, the Yamato-type (CY), based on their oxygen isotopic compositions and petrological features. The elemental compositional characteristics of the remaining six meteorites analyzed in this study, Y-86737 and Y 980134 (with CI affinities), and Y-86770, Y-86771, Y-86772 and Y-86773 (with CM affinities), suggest that these meteorites are all classified into the same chemical group CY. Based on the abundance of moderately volatile elements Mn and S, the twelve meteorites can be divided into two groups: one with levels similar to non-Antarctic CI and the other with intermediate levels between CI and CM. These results suggest that CY chondrites originate from two distinct parent bodies. To facilitate further discussions on CY chondrites, we propose naming the groups with compositions close to CI and CM as CYi and CYm, respectively.