Characterizing near-surface elemental layering on Mars using gamma-ray spectroscopy: A proof-of-principle experiment

NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS

卷:415

Article

Peplowski, Patrick N.¹  Wilson, Jack T.¹  Beck, Andrew W.¹  Burks, Morgan²  Goldsten, John O.¹  Lawrence, David J.¹ 

[1] Johns Hopkins Appl Phys Lab, 11100 Johns Hopkins Rd, Laurel, MD 20723 USA

[2] Lawrence Livermore Natl Lab, Livermore, CA 94550 USA

关键词: Gamma-ray spectroscopy;    Mars;    Sub-surface composition;    Geant4;   

DOI  :  10.1016/j.nimb.2017.11.016

来源: Elsevier

【 摘 要 】

Gamma-ray spectroscopy investigations characterize the chemical composition of planetary surfaces by measuring element-characteristic gamma rays with energies of similar to 100 keV to similar to 9 MeV. Over this energy range, the mean free path of a gamma ray varies from about 1 to 25 cm, therefore gamma-ray measurements sample subsurface composition. Many elements emit gamma rays at multiple, often widely spaced energies, so gamma ray measurements can in principle also be used to identify depth-dependent variations in subsurface composition. We report results from laboratory measurements and radiation transport modeling designed to demonstrate this capability. The laboratory measurements verified the presence of depth-dependent gamma-ray signatures, and were then used to benchmark radiation transport simulations that were used to model realistic Mars-like scenarios. The models indicate that compositionally distinct subsurface deposits, buried to depths of similar to 80 cm (125 g/cm(2)), can be identified using gamma-ray measurements. Going beyond identification to characterization (burial depth, relative composition of the layers) of the deposits requires knowledge of the vertical and horizontal variability in the water content of the near-surface surface materials, the local Galactic Cosmic Ray environment (magnitude and energy distribution), the depth-dependent neutron flux, gamma-ray production cross sections, and knowledge of the composition and column density of the atmosphere. The results of our experiments and models provided a basis for examining the utility of using orbiter- and lander-based gamma-ray measurements to identify subsurface deposits on Mars.

【 授权许可】

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