  Associated particle imaging (API) is a non-destructive nuclear technique for
the 3D determination of isotopic distributions. By detecting the alpha particle
associated with the emitted neutron in the deuterium-tritium fusion reaction
with a position- and time-resolving detector, the direction of the 14.1 MeV
neutron and its time of emission can be determined. Employing this method,
isotope characteristic gamma rays emitted in inelastic neutron scattering
events 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 characterized.
The system was tested with common soil elements and shown to be sensitive to
12C, 16O, 28Si, 27Al, and 56Fe. New aspects of our approach are the use of a
yttrium-aluminum-perovskite (YAP) scintillator, using a sapphire window instead
of a fiber-optic faceplate for light transport to the photomultiplier, and the
all-digital data acquisition system. We present a description of the system
with simulations and experimental results that show a position resolution on
the alpha detector of 1 mm, a depth resolution using a LaBr3 detector of 6.2
cm, and an angular resolution of 4.5 degrees. Additionally, we present
single-element gamma response measurements for the elements mentioned above
together with a comparison to Monte Carlo simulations (MCNP6).
