Theory and Application of X-Ray and Gamma-Ray Backscatter to Landmine Detection

This report discusses the theory and application of X-ray and gamma- ray backscatter to the problem of nonmetallic landmine detection. The fundamental interactions of X and gamma radiation with matter, including photoelectric absorption, Compton scattering, and pair production, are reviewed. The backscatter spectrum is analyzed in terms of the components due to single and multiple scattering. The variation of the backscatter spectrum with changes in the average atomic number of the scattering material and with changes in source energy is explained. Four different sourcedetector geometries are compared in terms of countrate for a given source strength, target-present-to- target-absent ratio, sensitivity to height variations above the scatterer, and sensitivity to scatter density. Theoretical and practical factors in the selection of sources and detectors are considered. Three techniques for compensating for height variations are discussed, the most promising of which is a K-edge-filter method.