Single-Sided Noninvasive Inspection of Multielement Sample Using Fan-Beam Multiplexed Compton Scatter Tomography

As aircraft age, corrosion forms upon unobservable surfaces, particularly at the junction of the sheet aluminum and the steel rivets used to attach the sheets to the airframe, degrading the aircraft's airworthiness. Previous research developed a noninvasive technique for the evaluation of the material composition of aluminum surfaces, utilizing the information encoded in the energy spectra of Compton-scattered gamma emissions. The spectra are gathered by a sixelement, high purity germanium detector array. A, first principles, deterministic computer code is used to reconstruct a two-dimensional map of the electron density of aluminum samples. Previous efforts to image pure aluminum samples suffered from: artifacts at sample boundaries, inaccurate determination of electron density values, and excessive sampling times. In this work images, of an oxidized aluminum sample including an iron insert meant to simulate a vertical two-dimensional slice through a steel rivet in an aluminum surface, have been reconstructed. Sample boundaries have been determined, and included in reconstruction.