Package and Large Object Profiling With a Gamma/Neutron Sensitive Detection System

This paper summarizes a series of experiments performed at Savannah River Site for the purpose of determining the ability of a parallel plate collimator to constrain a detectors field of view with the goal of identifying the location of sources inside packages. These experiments took place in several locations at SRS using different types of sources, detectors and geometries. Broadly, these included profiling a heat exchanger lay down pad, a control rod cask, a shielded compound containing sealand containers filled with discarded jumpers from the canyons on site and some lab tests. The collimator used for the testing is a parallel plate type collimator. This collimator consists of a series of lead sheets sandwiched in layers of expanded polystyrene foam. The foam, containing mainly carbon and hydrogen and being of very low density, is almost transparent to gamma radiation and serves to support the lead sheets. The arrangement of the lead sheets as parallel plates allows for large attenuation of radiation in directions at an angle to the collimator axis since these photons will have to pass through one of more lead sheets, with larger angles being more heavily attenuated. This allows for a constrained field of view for very low system weight increase, a major advantage for field applications.