Design of Mega-Voltage X-ray Digital Radiography and Computed Tomography Performance Phantoms

A number of fundamental scientific questions have arisen concerning the operation of high-energy DR and CT systems. Some of these questions include: (1) How deeply can such systems penetrate thickly shielded objects? (2) How well can such systems distinguish between dense and relatively high Z materials such as lead, tungsten and depleted uranium and lower Z materials such as steel, copper and tin? (3) How well will such systems operate for a uranium material which is an intermediate case between low density yellowcake and high density depleted uranium metal? These questions have led us to develop a set of phantoms to help answer these questions, but do not have any direct bearing on any smuggling concern. These new phantoms are designed to allow a systemic exploration of these questions by gradually varying their compositions and thicknesses. These phantoms are also good probes of the blurring behavior of radiography and tomography systems. These phantoms are composed of steel (ρ assumed to be 7.8 g/cc), lead (ρ assumed to be 11.4 g/cc), tungsten (ρ assumed to be 19.25 g/cc), uranium oxide (UO3) (ρ assumed to be 4.6 g/cc), and depleted uranium (DU) (ρ assumed to be 18.9 g/cc). There are five designed phantoms described in this report: (1) Cylindrical shells of Tungsten and Steel; (2) Depleted Uranium Inside Tungsten Hemi-cube Shells; (3) Nested Spherical Shells; (4) UO3 Cylinder; and (5) Shielded DU Sphere.