LBNL Office of science Department of Energy

Ion Beam Technology Group

Lawrence Berkeley National Laboratory

Accelerator Technology & Applied Physics Division

Carbon in Soil

Schematic of the API system

Carbon distribution in soil is intricately linked to soil health. However, repeatable measurements of carbon distribution typically require destructive sampling and laboratory analyses. Soil carbon distributions in both natural and managed landscapes significantly vary due to numerous factors related to topography, mineralogy, hydrology, land use history, and vegetation. In order to accurately inventory soil C distributions and dynamics over time, we are developing a new technique that relies on neutron inelastic scattering to measure elemental distribution. This approach can be used to image a volume of approximately 50 cm × 50 cm × 30 cm (depth) with a few centimeters resolution, for example the root zone of a plant. To achieve this, we use neutrons created in a deuterium-tritium fusion reaction. The products of this reaction are an alpha particle and a neutron. Due to momentum conservation, both particles are emitted in opposite directions in the center-of-mass frame. This allows us to measure the neutron direction by detecting the alpha particle with a position sensitive detector. The neutron can then induce an inelastic scattering reaction on a carbon nucleus present in the soil, and this event produces a gamma ray with a characteristic energy for the carbon isotope. Using a gamma detector, we measure these gamma rays, which allows us to perform time-of-flight analysis between arrival times of the alpha and gamma particles. Using the information from both measurements (alpha and gamma), we can reconstruct the spatial distribution of the carbon atoms and other elements in soil.


Funding is provided by ARPA-e logo under the ROOTS program.

Relevant publications:

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  • Mauricio Ayllon Unzueta, Eoin Brodie, Craig Brown, Cristina Castanha, Charles Gary, Caitlin Hicks Pries, William Larsen, Bernhard Ludewigt, Andrew Rosenstrom and Arun Persaud An Associated Particle Imaging System for Soil-Carbon Measurements (2019) journal web page bibtex
    @article{ Unzueta2019-vz,
    title = "An Associated Particle Imaging System for Soil-Carbon Measurements",
    month = "August",
    year = "2019",
    url = "",
    archivePrefix = "arXiv",
    eprint = "1908.00950",
    primaryClass = "physics.ins-det",
    arxivid = "1908.00950",
    author = "Mauricio Ayllon Unzueta and Eoin Brodie and Craig Brown and Cristina Castanha and Charles Gary and Caitlin Hicks Pries and William Larsen and Bernhard Ludewigt and Andrew Rosenstrom and Arun Persaud",