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Author: Admin | 2025-04-28
Would be imaged.[76]Explosive vapor detection[edit]A buried mine will almost always leak explosives through the casing. 95 percent of this will be adsorbed by the soil, but the other 5 percent will mostly dissolve in water and be transported away. If it gets to the surface, it leaves a chemical signature. TNT biodegrades within a few days in soil, but an impurity, 2,4-dinitrotoluene (2,4-DNT), lasts much longer and has a high vapor pressure. Thus, it is the primary target for chemical detection. However, the concentrations are very small, particularly in dry conditions. A reliable vapor detection system needs to detect 10−18 grams of 2,4-DNT per millilitre of air in very dry soil or 10−15 grams per millilitre in moist soil. Biological detectors are very effective, but some chemical sensors are being developed.[77]Honey bees can be used to locate mines in two ways: passive sampling and active detection. In passive sampling, their mop-like hairs, which are electrostatically charged, collect a variety of particles including chemicals leaking from explosives. The chemicals are also present in water that they bring back and air that they breathe. Methods such as solid phase microextraction, sorbent sol-gels, gas chromatography and mass spectrometry can be used to identify explosive chemicals in the hive.[78]Honey bees can also be trained, in 1–2 days, to associate the smell of an explosive with food.[78] In field trials, they detected concentrations of parts per trillion with a detection probability of 97–99 percent and false positives of less than 1 percent. When targets were placed consisting of small amounts of 2.4-DNT mixed with sand, they detect vapor plumes from the source several meters away and follow them to the source. Bees make thousands of foraging flights per day, and over time high concentrations of bees occur over targets. The most challenging issue is tracking them when a bee can fly 3–5 kilometres before returning to the hive. However, tests using lidar (a laser scanning technique) have been promising.[79]Bees do not fly at night, in heavy rain or wind, or in temperatures below 4 °C (39 °F),[80] but the performance of dogs is also limited
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