We’re in our car in line at the Canada/USA border going into the US (which took 2.5 hours to cross by the way).
Right before you reach the guard window there is a stop sign. At the stop sign are a handful of cameras. Oh both sides of the car are two pair of white panels - two about door level, two more about 9-10 feet up pointing down at the car. I’d guess the panels are about 10 inches square and perhaps 3 inches thick with a solid plastic looking facecover. Out of each panel is a rigid gray conduit that makes it way to a large stainless steel box with a fan on the side.
I’m going to make a (very slightly) educated guess here and say that they are basically radio antennae. I’m assuming these are similar to the ones found along the interstates near state borders. These (at the state border) read an electronic manifest from properly equipped 18-wheelers. I’m fuzzy on the details, but it is some type of system for tracking commercial vehicles crossing the border for tax purposes (I think).
Sorry to be so vague. Hopefully someone with a better understanding will come along soon and clarify it for us all.
Metal detectors detect conductivity, not density. I don’t think you could modify a metal detector to selectively detect lead or uranium, and if you were just looking for “any metal”, the truck carrying the lead would register a lot more strongly than its cargo. You could use x-rays to detect dense materials, but that would require an active source, which could pose a risk to people or photographic film, which most folks wouldn’t like. Or you could use naturally-occuring cosmic rays, but the detectors based on those are underneath the road, not alongside the vehicles.
These sorts of scanners use either high-energy x-rays or something called pulsed fast neutron analysis. When the fast neutrons hit the target, gamma rays are released. Absurdly complicated equipment detects the gamma rays and assemble the data of the direction they came from, strength, etc in a process similar to the processing done by a medical MRI scanner to form a 3-D image of the contents of the cargo container or truck. In addition to the imaging, the system analyzes the material and can directly determine the elements it’s made of. eg: aluminum vs iron, etc. In addition to looking for contraband (explosives, drugs, etc.) the system can also analyze and detecct hazardous materials to reduce the chances of inadvertent mis-handling.
Prettty cool stuff, and a friend of mine is a contract manager for one of the leading producers of these systems.
