Associated Particle Imaging (API) is a nuclear technique that allows for the non-destructive determination of 3D isotopic distributions. The technique is based on the detection of the alpha particle associated with the neutron emitted in the deuterium-tritium (DT) fusion reaction, which provides information regarding the direction and time of emission of the 14 MeV neutron. Inelastic neutron scattering leads to characteristic gamma-ray emission from certain isotopes, which can be correlated with the neutron interaction location. An API system consisting of a sealed-type neutron generator, gamma detectors, and a position-sensitive alpha detector was designed, constructed, and tested at Lawrence Berkeley National Laboratory (LBNL) for the non-destructive quantification of 12C distribution in soils. Additionally, the system is also sensitive to other elements present in the soil such as O, Si, Al, Fe, etc. It is capable of quantifying 12C at the percent level with a resolution of 2 cm x 2 cm x 7 cm for an hour of measurement. The first half of the dissertation describes the design of the system (using the simulation packages MCNP6, SPICE, and COMSOL Multiphysics) and the characterization of its components including the neutron generator, the position-sensitive alpha detector (YAP), the lanthanum bromide (LaBr) and sodium iodide (NaI) gamma detectors, and the systems used to observe the alpha and gamma signal. The second half focuses on data analysis techniques and presents initial experimental data benchmarked against simulations
