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Passive Gamma-Ray Emission for Soil-Disturbance Detection

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Technical Report

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U.S. Army Engineer Research and Development Center Hanover United States

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Humanterrain interactions, such as trafficking and excavation, cause changes to soil bulk density and porosity via compaction or mechanical bulking. The degree of compaction, as measured by bulk density, is a physical indicator of changing patterns of humanterrain interaction. Because soil radionuclide activity is a function of the mass content of the radionuclide and the volume of soil, the spectral signature of the naturally occurring soil radioisotope Potassium-40 40K should be sensitive to changes in the soil bulk density and reflect the soils disturbance history. If natural variations from geology and soil texture are systematic and predictable, one could map spatiotemporal bulk-density changes relative to some standard state as a metric of terrain disturbance. However, the natural variation in soil 40K content is unknown and may confound density determinations via radionuclide activity measurements. This study used a handheld sodium iodide gamma-ray detector to collect in situ gamma-ray spectra of four soils as a function of their potassium content, bulk density, texture, and water content. A statistically significant difference between the 40K activity of uncompacted and compacted soil suggests that in situ 40K gamma-ray emissions from soils are a sensor modality useful for soil-disturbance detection.

Subject Categories:

  • Nuclear Physics and Elementary Particle Physics
  • Soil Mechanics

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