1. Introduction: An important inspection problem, which bothers Custom officers all along, is how to determine the material of goods inside container. For example, the explosions, the drugs and other dangerous goods should be found definitely and automatically. This is also very important for anti-terrorism. The current container scanners, no matter which kind of radiation source is used, cannot fulfill this task. Because these scanners are based on the digital radiography technique (DR), and the images obtained are just only projection image. All goods inside container are overlapped in the projection image, and the gray scale is depended on the total mass thickness along the rays.
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