DIY Radiography

[Cyparagon]

X-Rays are electrons right?

No, Xrays are photons. Very short wavelength. There is currently NO good way of focusing them. The closest thing there is is bouncing them off of an array of very shallow inclines - that's how the space telescopes work I believe.

 

[RedCowboy]

Is this actual emitting X-ray radiation? It says backscatter but also 10 watts, so is it emitting or not?

I found this video and I know it's not relevant to our academic study but it is interesting and I wonder just what was " created "

 

[Sigurthr]

X-Rays are electrons right?, and electrons are sensitive to magnetic fields, so couldn't you use a deflection yoke, like they do in CRT's to "shape" the beam to something approaching the green pattern in your diagram?

Nah they're Photons as Cyp has pointed out. However, the x-rays come from the sudden deceleration of electrons within the tube, so it is conceivable to magnetically focus/steer the electrons into a manner which would focus the x-rays. This is what the wehnelt electrode does, and why I think it is worth it to give it a try hooking it up. Whether or not to try additional magnetic focusing I can't say.

Well, I have to hand it to you...what you have essentially done is figure out how to digitize x-rays with your own method. I think they use some kind of intensifier plate...read by TFTs...you are doing something really different.

How did you get the idea. I mean I have never heard of getting x-ray images in this manner.

I can't say it was a problem that I had to sit and think about an answer for really. Knowing the underlying physics and applied science for all the parts of the system individually, it seemed natural and certain to me that it would work as a whole. I suppose that's one of the nice things about having a multidisciplinary understanding or self-education; you can look at things from a different angle than others might. Likewise, they say restriction breeds creativity... had I the wealth needed to simply buy an industrial radiography unit like semiconductor labs or NDT outfits use I'd have never had to figure out how to do it my way with very basic means.

Is this actual emitting X-ray radiation? It says backscatter but also 10 watts, so is it emitting or not?

Backscatter x-ray is a relatively recent development and I don't have a good working knowledge of -how- it works. Cursory searches reveal it works by using low doses of x-rays and gamma rays (same photons, just different energies, the real differentiation is the source being man made or from an isotope) and instead of looking at the photons that get through the object, look at the photons which gets scattered off the object. Given that a lot of this tech is held up in proprietary documents it is hard to find actual data on its workings. Plus, it isn't regulated by any governing body since it isn't used for medical purposes.

The truly interesting bit is that there are systems which can look through the sheet steel of a cargo container and show the outlines of smuggled people inside. To my knowledge there's no photon energy which will both pass through **faraday-shielded sheet steel in great enough flux to yield a return image on the other side (that's TWO passes through an attenuating medium density substance) but scatter off of soft tissue enough to yield an image of the whole object exterior without the internal image.

** - thermal imaging can, but this isn't that
Sonar also can but that isn't electromagnetic, and isn't used here either.

There only a few methods of interaction with matter that x-rays undergo: Compton scattering, Rayleigh scattering, photoelectric effect/absorption, transmittance, and narrow angle reflection. The degree of scattering and PE absorption are inversely proportional with eV energy, transmittance is proportional to eV energy, and narrow angle reflection exhibits a complex nature based on the density and atomic structure of the angled surface, as well as what angle it is.

Anyway, if you wish to discuss backscatter further I recommend making a new thread for it. =)

 

[Cyparagon]

...it is conceivable to magnetically focus/steer the electrons into a manner which would focus the x-rays.

To be clear, that makes the emission area smaller; it doesn't focus the rays. The rays will always diverge from the emission area. It's only "focusing" in the sense the image may be more clear, but again, this is because the emission area is smaller, not because you've altered the course of the xrays.

 

[Andrew124C41]

Is this actual emitting X-ray radiation? It says backscatter but also 10 watts, so is it emitting or not?

RedCowboy, leave it to you do discover this kind of thing. I think I keep up but I had not heard of this. As far as I understand it is essentially using the energy bouncing off the object rather than the energy that penetrates.

As Sig mentions, it is really something when you think that this technology can penetrate sheet metal. I don't think it can be simple x-rays using backscatter because while x-rays at very high energy can penetrate some sheet metal I think you would not get a decent image. I could not find too much more..I am wondering if this comes from our friends at DARPA.

 

[ped]

To be clear, that makes the emission area smaller; it doesn't focus the rays.

Focusing is "post emission", is it not? are you saying that magnetism could influence the anode / cathode?

 

[Sigurthr]

To be clear, that makes the emission area smaller; it doesn't focus the rays. The rays will always diverge from the emission area. It's only "focusing" in the sense the image may be more clear, but again, this is because the emission area is smaller, not because you've altered the course of the xrays.

Aye, the x-rays won't be focused, but the emission pattern will improve from a smaller focal spot. The electron beam would be getting focused. Sorry for the ambiguity.

I do wonder if and how effectively a DIY x-ray lens could be built, but I'm not about to source the tungsten paneling or fabricate the louver system for it, haha.

@Ped the magnetic or electric field can alter the path of the electrons traveling from the cathode to the anode, altering the shape and size of the area on the anode that gets struck, which in turn alters the x-ray beam geometry.

 

[ped]

Yeah I was fuzzy on the whole emission thing..cathode electron emission or anode X-Ray emission..

 

[Sigurthr]

Yeah, it's hard to be precise without being verbose sometimes.

Thinking more on it, the unusual beam shape could possibly be because my filament/cathode is indirectly heating my wehnelt electrode to the point that weak thermionic emission occurs, resulting in a "secondary electron beam". Now, the wehnelt never gets to significant temperature, but heck, field emission occurs at "cold" states, so there's no reason that augmented emission from elevated temperatures couldn't occur. This would at least explain the strange emission characteristics I'm seeing. This makes me wonder if I should have some series resistance between the wehnelt bias and the electrode, in order to discourage it acting like a second cathode. Though, thinking about that as I write now, it's currently tied to cathode and thus at high potential difference with the anode, once it is isolated from the anode circuit it would no longer feel the anode's pull. This makes isolating the wehnelt bias even more important (and many systems -do not- isolate it).

 

[RedCowboy]

From what friends in the know have told me these are being used on houses as well, I don't know how deep your front yard has to be before it won't work.
The backscatter technology emits x-rays and analyzes the backscatter with amazing ability.
Suddenly I want to rent a backhoe and dig a root cellar, joking...hahaha... aww

http://www.quantumday.com/2012/06/coherent-laser-light-with-simultaneous.html


Apparently X-ray lasers do exist, it's not pocket sized but at 100,000 watts it's able to do the job.
Sure fiber lasers can do 150kw but not in x-ray, no weather be it rain or fog will keep the x-ray laser from it's target, I wonder what range it can achieve? If unfocused I wonder how many square meters of enemy troops it could sterilize. Spooky stuff.

 

[Sigurthr]

I finally got around to working on the power supply again today. What a freaking mess... gallons of mineral oil! Oh well it took forever to clean up (and there was NO spill) just from transfer on tools/gloves.

I added a -140V Wehnelt Bias supply and tested the output. To my surprise the output beam didn't really move much to be more centered along the nominal output path of the tube. It's not really a big deal though, it was obviously usable before. It does double the X-Ray flux output though! I kept with my modular design intention and made it so the wehnelt electrode can be externally biased or tied to cathode/filament for ease of use. I didn't have an isolated 140V supply so I have to run it off an isolated power source, which is a pain, especially since the 140V supply is bulky and unwieldy. I may look for a better solution in the future when I feel like putting more money into this. I'm not sure if it is worth it economically given it only decreases exposure time.

I did not do the full photographic procedure I normally use for quality radiographic results. This image was taken with a bare-bones imaging setup just to see if there was any change in beam positioning or focusing. It came out well enough to post though. It's my Kindle FireHD, which was left inside its protective case and placed in the beam path.

I also got around to doing the HV measurement while I was "under the hood" and full of oil already. Under full load the output is 45kV with a 2kVp-p ripple. Not bad at all! I estimated 50keV based on penetration ability, so being only 3keV off is pretty freaking good accuracy.


https://youtu.be/3QOe7t60GtI

 

[ped]

That's some fine detail there...how big is the original image?

Ped

 

[Sigurthr]

Original is 3024x4032 since I used my full spectrum 12MP camera. It'd be 16MP if I used my good camera.

The detail isn't bad but I certainly didn't optimize it. I could have elevated the x-ray source so the target was in the primary lobe of the x-ray beam. I also just propped up the target against the x-ray cassette, instead of affixing it so it is perfectly perpendicular. Any spacing between target and cassette causes diffraction blurring. I also could have halved ISO and doubled exposure to get much less pixel noise. As I said originally, this was just a quick setup!

 

[Cyparagon]

It's an analog image originally, and is limited in detail by the size of the electron bombardment zone, and the quality of the fluorescent imaging plate. It doesn't make sense to talk about an analog image in pixels, since there are none. I'm not sure what the analog equivalent is, though.

 

[Sigurthr]

I'm not sure what the analog equivalent is, though.

It would be phosphor crystal size * phosphor crystals per inch. Good luck finding that data though!

You're totally right btw. However, I do not feel as of yet that I have reached the point where the digital resolution is approaching on the analog resolution. Thermal pixel (sensor) noise is the dominant limiting factor here. If I had a large format camera (APS-C or larger), a wide aperture wide angle lens (F2 15mm or wider), and a jig that allowed easy mounting of the camera such that the lens is guaranteed perfectly parallel with the cassette I could greatly enhance the sharpness and detail quality. Still though, I think the results I'm getting are pretty good.

 

[ped]

Pretty good? their fantastic. What I'd love to see is how good it is at picking out different materials.
Next time you set it up, put a baggie of flour or other narc facsimile and see what it looks like.

Ped