Chapter 2 OVERVIEW OF THE PROPOSED STUDY

This chapter gives an overview of the proposed study. To define the illicit material detection problem, in Section 2.1, the types of illicit materials are first introduced. The environment in which these illicit materials need to be detected is also carefully described. In Section 2.2, x-ray physics is discussed in detail. In Section 2.3, the principle of illicit material detection using x-ray technologies is discussed. A review is then given to different types of x-ray technologies that can be used for illicit material detection. This occurs in Section 2.4. X-ray technologies provide the ability to determine an object’s density and Zeff information. Knowing those two pieces of information about an object, its material type can theoretically be uniquely determined. Section 2.5 discusses the sensing technologies and other related problems needed to derive these two pieces of information. In order to derive R, a Zeff-related information, and L, a density-related information, an object’s true gray levels must be determined. Section 2.6 sets the research goal for this dissertation, which is to develop an advanced image-processing system in order to reveal an object’s true gray levels. Section 2.7 describes the hardware of the multiple sensor system that was used to collect x-ray images used in this study. Finally, Section 2.8 summaries the important points that are presented.