Landmine Detection by Scatter Radiation Radiography.

The application of scatter radiation radiography to the detection of buried nonmetallic antitank landmines is examined. A combination of calculations and measurements is used to address the problem. The primary calculation tool in a Monte Carlo photon transport code. Measurements are made with an x-ray source, sodium iodide detector, and soil box positioning system. The soil box containing a model of a nonmetallic antitank mine is moved beneath the x-ray source to simulate both the forward motion of a vehicle transporting the detection system and raster of the beam to search a path of sufficient width to allow safe passage. Calculations are used to suggest mine detection mechanisms and to optimize geometric parameters and x-ray beam quality. Measurements are used to validate the calculation results for a small detector and produce images of buried mines. The calculations are extended to large area detectors which are required to provide path searches of approximately three meter widths. Environmental parameters such as height sensitivity, soil density and moisture content, and inhomogeneities are examined in both calculations and measurements. Power requirements are also addressed. A system based upon detector collimation to emphasize differences in the multiple scattered components, characteristic of soil and the explosive found in mines, is found to be capable of mine detection at depths of burial of at least 7.5 cm at power levels compatible with portability, and at speeds, path widths, detection probabilities and false alarm probabilities consistent with operational requirements. Detection at greater depths is possible in soil recently disturbed by mine burial. Images of holes refilled with loose soil can be distinguished from those of buried mines by their characteristic features. However, the refilled hole images bear some resemblance to those of mines laid on the soil surface. A compound detector, consisting of both collimated and uncollimated regions, can be used to overcome this problem and increase the probability of detection of mines buried at shallow depths.