At 07:42 PM 1/10/01 -0800, you wrote:
>Interesting stuff--but by density I meant the actual
>materials themselves. For example, GPR can be used
>(given favorable soil conditions) to detect certain
>materials which lie beneath the surface of the ground.
>This is acomplished via a return signal. It is also
>possible using other technologies to "see through"
>concrete walls. What I'm wondering is if there might
>be some way to emit a signal the return of which will
>tell you what element you're looking at--uranium or
>lead, for example. Such a signal would need to pass
>freely through containers made of wood or sheet metal.
>Ideal would be a signal which was ONLY reflected by
>the target element(s).
Well, the only signals i know how to use are electromagnetic and nuclear.
X-rays and gamma rays easily penetrate normal thicknesses of steel - as I
referred to with the "whole truck" radiograph. It should be fairly easy to
pick out "strange" arrangements of internal parts using this.
Neutron activation would cause a burst of fission products - neutrons,
gammas, and the like - and might not be the best way to check for a live
Although, a SHORT neutron burst might not cause any embarrassing side
All of these technologies assume the importer of such devices uses normal
shipping channels, and containers that can be inspected with methods that
are unhealthy for living creatures.
Perhaps a "sniffer" looking for nitro compounds? These are already
available, and i think I read of some going into service in US airports,
looking for conventional explosives. Again, the detector has to be fairly
close to the item in question.
Unfortunately, there is no physical phenomenon I know of that will only be
reflected by certain elements. Spectroscopy comes close, as does NMR, but
both require an unobstructed line of sight to (or through!) the material to
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