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Driving X-Ray tube with ignition coil.

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zippotix

Thu May 08 2014, 03:43PM

Registered Member #5208 Joined: Thu Jun 07 2012, 06:12PM
Location:
Posts: 86

Hello, I'm planning to run a X-ray tube with ignition coil driven by dimmer and 0,680uF-1uF cap. These tubes are usually ran in uA range. My question is, is the current too big at capacities I given? The iggy coil outputs 40-50kV, depending on dimmers cycle, so I guess voltage is ok?

Also, I know CRT vacuum tube can be used as a low-power x-ray tube alternative, but isn't 40kV+ too much for them to handle?

Eleccentric

Thu May 08 2014, 04:50PM

Registered Member #33460 Joined: Tue Aug 27 2013, 06:23PM
Location: Seattle
Posts: 46

Two problems I see:

You want DC for an X-ray tube, and your ignition coil will produce AC pulses. The tube may still create X-rays with AC, but depending on what type of tube you are using this could result in a much more diffuse emission, precluding using it for imaging. A LOPT/flyback transformer with built-in rectification would be much more suited to your application.

And yes, your setup is capable of delivering much more power than a tube designed to draw microamps will need. A high value resistor should be put in series with the output, if nothing else.

teravolt

Fri May 09 2014, 07:31PM

Registered Member #195 Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111

use this instead

zippotix

Sat May 10 2014, 12:21PM

Registered Member #5208 Joined: Thu Jun 07 2012, 06:12PM
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Posts: 86

Hmm, I drived a flyback with a dimmer before, and while it worked I was concerned the diodes would fail; the output voltage was quite high. Eleccentric, do you know how much abuse these diodes can handle? I can't find info on this one.
Teravolt, wouldn't tube ''pulse'' with marx?

zippotix

Tue Jun 03 2014, 04:25PM

Registered Member #5208 Joined: Thu Jun 07 2012, 06:12PM
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Posts: 86

Sorry for double posting, but if I'd use for example DY86 or some other rec-tube, would input still require rectification? Take a look at this

Conundrum

Tue Jun 03 2014, 06:01PM

Registered Member #96 Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4061

Normally rectification is needed, as otherwise you will get X-rays emitted from all over the tube and not just at one end.
The tube will also get very hot and fail, see earlier comment about resistors.
1Gohm sounds about right, will limit it to sensible dose levels.

General rule, if you can see the tube glowing green or blue in one small spot or in a band around the tube for larger ones then it is emitting potentially dangerous levels of radiation and needs shielding.

zippotix

Tue Jun 17 2014, 11:45PM

Registered Member #5208 Joined: Thu Jun 07 2012, 06:12PM
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Posts: 86

I used a DY86 tube instead, and it works. Radioactivity counter app gave almost 3k counts for few seconds of operation. I guess I really need some shielding, call me paranoid but this freaked me out.
Are x-rays damaging the CCD? Also, is it correct that 100CPM equals 1uSv? Of course I don't know the quality factor but some say it's the same for gamma and x-rays, that is 1.

zippotix

Sun Jun 22 2014, 08:11PM

Registered Member #5208 Joined: Thu Jun 07 2012, 06:12PM
Location:
Posts: 86

You guys were right about rectification, it shoots everywhere. I had this idea to run dimmer on rectified mains, but wouldn't it destroy it?
Here's the video of it operating at maximum voltage, that is about 50-55kV

Eleccentric

Mon Jun 23 2014, 04:08PM

Registered Member #33460 Joined: Tue Aug 27 2013, 06:23PM
Location: Seattle
Posts: 46

Yes, the dimmer will only work on AC. You need to rectify the high voltage output itself. Accurate measurements of X-ray output are not something I know much about, but from what little I've picked up in regards to using Geiger counters, in this sort of setup it is much easier to pick up the repetition rate of bursts of emission rather than the actual count rate. Perhaps your sensing method has similar limitations, or even worse ones. From what I've read (in just the past few minutes) I'm going to guess that you are using a cell phone application to detect the radiation, and I should warn you that this is DEFINITELY less accurate and reliable than a Geiger counter, which is already an imperfect tool for measuring relatively low-energy X-rays.

Most of the radiation from this kind of setup will be part of what is called "white radiation" or bremsstrahlung, IIRC, which covers the whole spectrum from infrared up to X-rays equal in keV to the your maximum applied voltage, about 50kV in your case. Almost all of these X-rays will be absorbed by your body, rather than passing straight through. Mammograms are about the only type of X-ray that uses such low energies. These levels are filtered out of the emissions from medical devices since they are useless for dense tissue imaging and would only add to the ionizing radiation exposure.

Lead roof flashing could be of great use to you, but I'm no expert, so don't take it from me that it will make any setup of yours safe to operate.

Why do you want these X-rays? It's nothing to be fooling around with just for the hell of it. Making X-rays is easy; doing something useful with them safely is hard.

zippotix

Mon Jun 23 2014, 09:11PM

Registered Member #5208 Joined: Thu Jun 07 2012, 06:12PM
Location:
Posts: 86

This is the application I use

I know it's probably not as accurate as a Geiger counter but out of curiousity I tried it

.
I switched it on remotely, using a long extension cord, there is like 1m of concrete between me and the tube, and since those X-rays have low energy, I think they won't reach me (I still worry though)

I was hoping to use it for pictures of small, not too dense things. I have intensifier ''sheet'', but till I figure out how to rectify the coil's output I won't even bother. Thanks for advice, too, gotta look this white radiation up.

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