Wallace, G. 2006 Gamma ray backscatter imaging. Lower Hutt, N.Z.: GNS Science. GNS Science report 2006/04 13 p.
Abstract: The backscatter of low energy gamma rays from a radioisotopic source has been investigated to determine its usefulness for imaging beneath surfaces. The approach taken has been to tightly collimate the incident gamma rays, but leave the detector uncollimated. This is in contrast with the more usual technique where both beams are tightly collimated to define a scattering volume element. Applications for simple sub-surface structures composed from low-atomic weight materials are feasible, but . Lower Hutt, N.Z.: GNS Science. a priori knowledge of what is being imaged is essential for reliable interpretation of the results. In comparison with transmission radiography, and in spite of the lack of detector collimation, the backscatter process is slow, and of inferior spatial resolution. For these reasons, backscatter imaging applications based on radioisotopic sources will be very limited. A useful application was successfully developed that enables backscatter to be used to determine wall thicknesses in timber of varying densities. In conjunction with a simple transmission imaging system, the addition of backscatter measurements provides a worthwhile safety check. (auth)