backscatter X-ray detects the radiation that reflects from the target.
too see whats inside containers, trucks and vehicles. This technology is really expensive and at least some sort of little
car must be used to carry it.
Seems the amount of the X-Rays is very low so there should be no big health risk or polluting the ground with radiation.
The depth of course depends how thick and hard the soil or ground is and how good is the contrast of the finds compared
with the other stuff. Of course because "lightweight" and lowmineralic stones are easier to penetrate than metal depending
how thick those metal finds are they may be still good visible below thick layers of rock etc.
Seems this technology even is adjustable to see very clearly the content of a region which is behind a "view blocking wall"
- like in trenches / different layers and there also is a way to recognise if the material is organic or not.
I have no idea how deep it may be able to penetrate into the ground - perhaps up to 3 meters depending how massive is the soil.
more info:
http://en.wikipedia.org/wiki/Backscatter_X-ray
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