Workin' on the surface of the sun!

[Bret]

Like I said besides my woes at home work has been keeping me pretty busy too. And let me tell ya – working out-doors this time of year because of the heat can make even the simplest of service calls extremely challenging.

Anyway I was doing some demos the other day and took the following video that some of you folks might get a kick out of.

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Oh & trust me on this - with the mercury was hoverin’ somewhere around 115F only a foolish child wouldn’t be wearin’ a sombrero too.

Cheers,
Bret

 

[Bret]

Heres a "still shot" takin' from another out-take video of the instructional part.

Heres the images from the above scan.

Transmission side

Z-Backscatter side

 

[DrEntropy]

That brings up sooo many questions!! Sensor is apparently the ouitrigger and the entire length is the "receiver"... beam distributed with mirrored surface? On some king of gimbaled spinny-turny "disco-ball" thing to distribute it the length of the pickup?? Stepper motors from Hades! Looks like fun stuff.

Neat.

 

[Bret]

Well Doc,

Believe it or not there is a huge spinning (5ft in diameter) disk/wheel that we call the chopper wheel that spins vertically and is aligned with the transmission beam detector (outrigger).

In the middle of that spinning disk/wheel is a large lead housing or hub that houses a 450KV X-Ray tube. On the spinning disk/wheel there are 4 hollow spokes that allows x-rays to escape in the shape of pencil thick x-ray beam. This beam passes through the thin skin of the exterior of the x-ray truck.

The upper image is the Transmission (conventional) x-ray scan. That is made from the aforementioned pencil thick x-ray beams that are coming out of the spinning chopper wheel (~280 rpms) that allows the sweeping x-ray beam to pass through the target (my truck) and hit the detector on the other side. Each sweep of the from each spoke equals one line of pixels that appears on a computer monitor in the rear ops room as the truck moves past the vehicle.

The second image is the Backscatter scan. This image is created almost exactly the same way as the transmission image is except in this case we are looking at the x-rays that are “reflected” back from the target and hit the detectors on either side of the large panel on the side of the x-ray truck.

See the trick or FM (Freakin’ Magic) behind backscatter is that x-rays not unlike many types of like any emissions can be reflected or scatter. Not unlike how visible light is refracted in different directions as it passes through a prism, x-ray can be reflected or “scattered” thus the name Backscatter. But the reason the back scatter looks so different is because of the z-rating or atomic structure of the target. So denser (high Z) materials like metal will be harder to penetrate, while less dense (low Z) materials like plastics & organics will be easier for the x-rays to pass through.

So the transmission image will be really good at detecting & highlighting denser objects and gives the skeletal image you see above. Whereas the backscatter image will be better suited for detecting organics like drugs & plastic explosive. The two images together give the operators a good perspective of what is actually in the targeted vehicle.

Don’t know if I’ve helped clear things up for everyone or confused you more.

 

[kennypinkerton]

Very Cool. Is there any possible danger to the truck driver from the x-rays?

 

[Bret]

Very Cool. Is there any possible danger to the truck driver from the x-rays?

Nope, none what-so-ever. In fact stopped counting the number of scans my truck has had years ago. But the extremely low dose rate on this type of design is it's lower than background radiation and one of its major advantages (i.e. a selling point).

The Gamma (live sources) are the ones you got’a worry about. Ours only creates x-rays when under power, whereas a live source is always emitting radiation and is only as safe as it’s shielding.

 

[kennypinkerton]

Hospital x-ray must be a lot stronger, why else would they lay that big heavy lead lined glove over your lap to get an x-ray of your arm. Oh, and they always make me feel really good about it when they leave the room to go behind the sheild :wink:

 

[Bret]

Actually the truck uses 450KV industrial x-ray tube, whereas most medical usage x-rays are 125-150kv systems. But the exposure isn't based on power as much as it is how the x-ray is manipulated. But what we are dealing with is two totally different applications.

Without getting too technical - Medical x-ray systems typically employ an wide open shutter with a collimator to cover areas of the body being scanned. While the our security screening system in this case uses hundreds of small pencil thin x-ray beams that come out of the four hollow spokes on large chopper wheel as they pass over the x-ray tube's opening. That chopper wheel is spinning at about 250-280 rpms. This is called flying spot technology – that still allows the power & penetration, but it is spread over a larger area, thus diminished exposure.

 

[kennypinkerton]

I get it, more power, but pulsed quickly in small doses. Makes sense.

 

[Bret]

Glad to help Kenny,

Just don't get me started on the attributes of a fixed tungsten anode vs. a rotating one. :wink:

But regardless give me a conventional x-ray or a high energy 6MEv source system over a live gamma source any day. Couldn’t pay me enough to work with the “live” stuff.