Abstract
Carbon sequestration in soils represents an important opportunity to
reduce the amount of greenhouse gases in the atmosphere and thereby
offsetting the effects of climate change. To monitor carbon
sequestration accurate measurements of soil carbon are needed that can
be repeated over several growing cycles. Furthermore, soil carbon is an
important indicator of soil health; accurately measuring carbon
distribution is therefore important for informing land use management
practices. We are developing a new instrument that images a volume of
approximately 50 cm × 50 cm × 30 cm (depth) with a few centimeters
resolution by applying neutron scattering techniques. Contrary to
current coring methods, this approach is non-destructive, samples a
large area, and allows real-time analysis of the soil carbon density. In
this technique a neutron and an alpha particle are created in a
deuterium-tritium fusion reaction. Due to momentum conservation the two
particles move in opposite directions. Creating the particles in a small
point source allows us to calculate the direction in which the neutron
is moving by tracking the associated alpha particle using a position
sensitive detector. The neutron can then enter the soil and
inelastically scatter off atoms in the soil, creating an
isotope-specific gamma ray in the process. Measuring the energy of the
gamma ray allows identification of the isotope. Measuring the
time-of-flight between the alpha detection and the gamma detection
together with the direction of travel of the neutron allows the
calculation of the 3D position of the scattering center. Using this
Associate Particle Imaging (API) technique 3D density plots of carbon,
oxygen, silicon, and aluminum can be obtained. In this poster we present
first results from applying API to pre-mixed and standard soil samples
in a laboratory setting (field tests are planned in the future). We will
compare measured data to neutron-transport simulations and discuss our
data analysis algorithm to reconstruct the carbon density in the soil
from API data. We will further discuss achievable resolution and time
requirement for measurements in the field. The information, data, or
work presented herein was funded by the Advanced Research Projects
Agency-Energy (ARPA-E), U.S. Department of Energy, under Contract No.
DE-AC02-05CH11231.