Material Characterization and Flaw Detection, Sizing, and Location by the Differential Gamma Scattering Spectroscopy Technique. Part I: Development of Theoretical Basis

Abstract

The differential gamma scattering spectroscopy technique is a novel means of nondestructive testing using Compton scattering to determine local density perturbations in a test sample. The test sample is irradiated with a narrow collimated beam of gamma rays, and the scattered radiation field is detected in a transversely placed high-purity germanium detector. The detector provides excellent energy resolution so that a detailed energy spectrum can be obtained. This spectrum is then subtracted from a reference spectrum that was collected from a well-known, unflawed sample to obtain the differential spectrum. This differential spectrum primarily contains information characterizing the flaw. Using the relationship between the scattering angle and the scattering energy that characterizes Compton scattering, the single-scattered spectrum can be used to determine the location of scattering and, consequently, the density distribution along the portion of the primary beam path that passes through the sample. An attractive feature of this technique that sets it apart from other Compton scattering techniques is the ability to detect flaws both on and off the primary beam path.