Use of isotopic gamma sources for identifying anti-personnel landmines.

Density is one of the indicators that can be utilized to distinguish an explosive material from an innocuous anomaly. Compton scattering of photons can be used to provide such density indication. Although X-rays have been employed for this purpose, isotopic gamma-rays offer some advantage for use in a portable device, because of their small size and self-powered nature. Radioisotopes were considered in the 1970's by the US Army. This work re-examines the utility of these sources for the detection of shallowly buried anti-personnel landmines. Monte Carlo studies indicated that the most effective configuration for identifying and locating a buried landmine should employ a collimated (241)Am source, along with a set of well-collimated detectors. Experimental measurements verified the feasibility of the proposed method and demonstrated the detectablility of mockups of landmines as small as 45 mm in diameter buried near the soil surface, or mockups larger than 80 mm in diameter buried at a depth of 80 mm, in light soil. In heavy soil, targets 80 mm in diameter were detectable at a depth of 30 mm. The use of the low-energy (60 keV) (241)Am source makes it possible to design a light-weight hand-held device that can augment other methods of detecting plastic landmines.