X-ray imaging techniques based on Compton backscatter permit inspection and screening
of sea containers, a wide variety of vehicles, luggage, and even people. In contrast to
more commonly used transmission images, backscatter imaging involves positioning both
source and detection apparatus on only one side of a target object. This presents the user
with inspection opportunities in situations that may be extremely difficult, if not
impossible, for transmission systems that require access by the detector subsystem to the
opposing side of the target. The backscatter image is somewhat akin to a photograph of
the contents of a closed container, taken through the container walls. Techniques for
producing X-ray images based on Compton scattering will be discussed, along with wideranging
examples of how systems based on these principles are used to perform
inspections for both security applications and for the detection of contraband materials at
ports and borders. Potential applications in the area of non-destructive evaluation will
also be considered. Differences in the type of information displayed by transmission and
backscatter images will be highlighted, and tradeoffs between backscatter image quality
and interpretability, scan speed, effective penetration, and X-ray tube voltage will also be
discussed. The method used in scanning the target object results in an extremely low
radiation dose, a result that significantly broadens the application spectrum for this
imaging technique