Since its inception in 2008, Linatron Mi6 has been the standard x-ray source for cargo inspection. It produces interlaced dual energy (6MV and 3.5MV) x-ray pulses that enable material discrimination scan in a single pass. Both pulse-to-pulse and longer term stability has been improved. With Linatron Mi6 as the x-ray source, it is now possible to achieve a continuous material discrimination scale, instead of only dividing materials into four classes: organic material, inorganic material, metals and high atomic metals. Other advanced material discrimination features include virtual layer peeling and trust rating. Energy sensitive imaging detectors can extend material discrimination in thin-object region. Although our Linatron Mi9 Linatron, which produces interlaced pulses of 9MV and 6MV x-ray pulses, provides even better material discrimination performance as well as better radiographic performance, it is not as widely used due to increased imaging system size and higher cost of safety shielding.

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A technique producing an optical effect that is unaffected by rigid body motion is described. It is shown that the resulting interference fringe pattern is proportional to the change in model thickness, which for the case of plane stress is proportional to the sum of the principal stresses, and thus provides a full field isopachic fringe pattern. This method combines holographic interferometry and the moiré effect. Double exposure holograms are made from both sides of a model before and after deformation. The two sets of holographic interferometric fringes thus obtained are treated as random grids, and the superposition of these two grids produces a moiré effect that is free from the effects due to rigid body motion. The theory is experimentally confirmed with several examples, and limitations of the techniques are also discussed.

This paper presents a new coherent optical method whereby the partial derivatives of the contour of an object are measured. The object to be studied is immersed in a refractive medium and is imaged by a camera with a shearing device. The processed photographic plate which has been doubly exposed in the image plane with the refractive medium changed between the exposures can be Fourier filtered to yield a fringe pattern depicting derivatives of the surface contour with respect to the direction of shearing. This new method enjoys the advantages of being simple and less demanding in vibration isolation, coherence of light source, and film resolution.

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