PIs' proposed the construction a high-energy backscatter imaging system designed for nondestructive testing of metals and other high density materials. Such a system will be useful for applications where high density prevents the use of Compton backscatter and where air gaps prevent the transmission of noise ratio because of the high yield of electron/positron pairs from high-energy X-rays and the near-isotropic nature of the resulting bremsstrahlung and annihilation radiation. PIs' previous Monte Carlo simulations show that this backscatter system is capable of imaging materials to depths that permit the exit of 0.511 MeV annihilation photons and bremsstrahlung photons composed primarily of bremsstrahlung and positron-annihilation radiation, the spatial resolution and contrast discrimination of the system are strongly dependent upon the mean free paths of the electrons in the materials imaged. For this reason, it is necessary to perform mathematical calibration of the raw scatter profiles to obtain information about the shape, depth and composition of the subsurface components. This technique has no substitute in existing nondestructive testing.
