New, low-dose 1 MeV cargo inspection system with backscatter imaging

A new intermediate energy (1 MeV) x-ray source is described which uses a cw electron linear accelerator created specifically for this application. This source has been installed in the hub of a hollow-spoked rotating wheel to form a scanning beam of x-rays. As cargo is transported through the inspection tunnel at speeds up to 6" per second it is raster-scanned by this beam to form digital images of the backscattered as well as the transmitted x-rays. The system will be described in detail, and sample images of a heavily loaded 8' wide ISO container will be presented. Environmental radiation due to the x-rays scattered from the cargo itself will be discussed in the context of the tradeoffs between penetration, spatial resolution, x-ray energy, and x-ray flux.