Initial Investigation of the Small Feature Detection Capability of the ORNL Fast Neutron Tomographic Imaging System

A variety of fast neutron imaging simulations and measurements were performed to investigate the spatial resolution and small feature detection capability of a version of the Oak Ridge National Laboratory fast neutron tomographic imaging system. Two image quality indicators were examined: (1) a variety of long steel pins embedded axially in the interior of a polyethylene cylinder, and (2) a variety of short steels pins embedded radially in the surface of a polyethylene cylinder. Measurements demonstrated detectability of about 3 mm. Further data analysis may show improved detection performance and allow a more precise determination of the spatial resolution. Our current simulation code takes only partial consideration of the DT generator neutron production spot size, with neutron production effectively originating at a single point. Simulations showed that features less than 2 mm should be detectable with an improved generator. Our current ING-27 DT generator has a neutron production spot size of about 3.5 mm, which appears to be the limiting factor at present. Generators with spot sizes as small as 1 mm are commercially available. Higher-power, small–spot size associated particle generators are at the prototype stage and are expected to be commercially available soon.