Lateral migration radiography: a new x-ray backscatter imaging technique

Abstract

A new Compton backscatter imaging (CBI) technique, described as lateral migration radiography (LMR), has been developed and applied successfully to two difficult diagnostic problems: Detection of buried, plastic landmines, and detection of material flaws which lie close to, and parallel to, a surface, the method is based on image contrast generated by alteration of photon lateral migration relative to the illuminating beam direction. It is extraordinarily sensitive to density and/or atomic number variation along the photon lateral-direction travel paths. In LMR, relevant information-carrying photon detection efficiencies are two to three orders-of-magnitude greater than other CBI techniques such that the electric energy requirement for x-ray generation is only about one joule per acquired image pixel. The resulting small product of pixel illumination dwell time and x-ray generator electric power implies that current, easily accessible technology can be used to fabricate LMR systems with practical usage protocols. Three have been designed and built at the University of Florida: A laboratory device for perfecting buried landmine acquisition; a mobile system for field-demonstrating landmine detection; and, a laboratory system for detection of material defects in small structural parts. The LMR images, acquired in a laboratory landmine detection setting, are so definitive that identification of the mine-type, as well as presence, can be often accomplished. Results of a field test are near-perfect, both in determining buried landmine presence and in lack of false positive response. Images acquired in material flaw detection indicate ability to detect lateral cracks or delaminations with thickness less than 100 microns, as well as corrosion on surfaces between layers of structural sheets. These applications provide evidence of the viability of a new, one-sided x-ray radiography technique which images hidden structures of objects which have here-to-fore been difficult, or impossible, to detect with practical image aquisition times.