Monday, November 26, 2012

DIY X-ray backscatter imaging system (airport body scanner)



I built an X-ray backscatter imaging system from parts found on eBay. This system works by scanning a very thin beam of X-rays across the target, and measures the amount of backscatter for a given beam position. The beam is scanned mechanically by a rotating chopper (collimator) wheel, and by tilting the rotating wheel on an orthogonal axis. The output image is generated on an oscilloscope by matching the horizontal scan speed to the rotating wheel, and using a potentiometer to measure the vertical axis position. The scope's brightness (z axis) is controlled by the amount of backscatter signal received by a large-area detector. Thus, the image is constructed bit by bit. I used a long-exposure shutter on my camera to see the image formed by the moving oscilloscope trace.

http://www.google.com/patents/US5181234

7 comments:

Anonymous said...

Great job, Ben!!! I had dreams of building my own version of this, but it was only ever a dream.

You prroject came out fantastic. Will you be making a refined version 2?

Have you thought of using any sort of far/extreme UV laser for your penetrative beam source? Or how about radio/silicon X-ray detection, like using a diode array? They might not have the required sensitivity, however.

Have you thought of modulating the beam with a carrier frequency (like IR communication) to increase signal?

~~Wizzard

Anonymous said...

Fantastic work.
Would it be possible to log the timing of the received radiation to assign colors depending on the time it needs to penetrate objects? Kind of like a layered view of the exterior structures which could produce a MRT like picture?

[Woss Mimp]

Anonymous said...

Great build as usual!
Could you walk through the rotor & motor assembly works in a bit more detail?
I paused the video on your cad render and the quick shot of the tapered roller bearing, but I couldn't figure out what rigidly coupled to what.

Also, I like the ad reduction at the bottom of the page. They got me anyway, as I thought the one pixel wide ad was a spectral line, and figured you put an easter egg in your site.
Hope the ad click helps out your blog. :)

Anonymous said...

@Anon ("Fantastic work...")

You could do this with a few passes (or maybe another method) combined with varying the X-Ray power (between 20 Kev and 50 Kev as per the patent's info, right Ben?)

More powerful X-ray reflect more overall; Lower powered X-rays reflect much less with higher-numbering elements than higher-powered X-rays.

By scanning one pass at say 20Kev and one pass at 50Kev and applying each pass to a color, one could readily see the different between organic (reflecting mostly at all energies), an aluminum/bone/magnesium thing (refecting at lower-power passes, but absorbing at higher ones), and an iron/nickel thing (absorbing at all energies).

Applying this detector with some auto-leveling control (expo on the output from the detector), a really nice false-color image would be possible.

~~Wizzard

Anonymous said...

Pretty impressive. But you should take into account the amount of radiation that you receive. Radiation can cause cancer etc.

Anonymous said...

Very impressive.

In reference to some of the comments, this is backscatter, not through beam. It does not look at the attenuation through an object. That might require more x-ray tube current to get sufficient events to measure, and potentially higher energy for more (deeper) penetration. The detector circuitry might need to look at the intensity as well as the number of events.

I would like to see the parts list.

Nitrous said...

Hi Ben
Can the detector be calibrated for use in an XRF system?
Doug

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