Recently, I've bought a tiny USB powered spark gap bipolar Tesla coil (rated at 15 mA and (35-50)kV). I am a pretty interested in spectroscopy, so I played around with the tesla coil and a couple of Neon bulbs (among others) from which I could get a pretty decent Ne spectrum.

The other day , I was wondering if I could build myself a partially evacuated Argon tube which could be powered by the tesla coil.And so I went to the lab to pick a "gas collector tube", I purged it with pure Ar several times, then I connected it to the vacuum pump and I sealed it.

Surprisingly, it worked! (see photo below).

Then I wondered if it might be producing some low energy X rays (I really doubt it but I decided to test it with an old Ludlum Geiger counter)and indeed the Geiger counter showed quite a high reading.

So my question is: was it really producing x rays as a consequence of the electron impact towards one of the electrodes? or was it simply the static interference of the tesla coil with the Geiger counter?

Honestly, I really doubt that it was really producing x rays, due to the following points:

  • The vacuum pump used is not a high efficient rotary vacuum pump , so the final pressure is far from an ideal vacuum.

  • The plasma is very faint (the picture is a 5 second exposure shot)

  • The Geiger counter shows the similar response whenever it is close to the tesla coil (even if the vacuum tube is not connected)

  • The signal response is very drastic, that is, the Geiger counter only shows a significant reading when it's just a few cm form the tesla coil, if not there is no signal at all.

What do you think?

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  • $\begingroup$ The fact that it does seem to be the Tesla coil and not the tube that is triggering the Geiger counter would seem to tell against the idea that the Geiger is recording x-rays. You need to get the experiment working as far from the Tesla coil as you can to rule out your valid conjecture that it could be interference from the coil. However, if you google "bremsstrahlung spectrum", you'll find that between 35kV to 50kV is where bremsstrahlung efficiency is really picking up. I'll leave someone more knowledgeable with these kinds of calculations to answer, but, if the Geiger is not ....... $\endgroup$ – Selene Routley Aug 29 '17 at 12:16
  • $\begingroup$ .... picking up x rays, it's either because the Geiger isn't sensitive enough and / or the supply current isn't high enough (there aren't enough events). 35kV to 50kV should probably be giving you significant bremsstrahlung. Also note, however, that the spectrum and efficiency does depend on the target - you're electrode is probably quite low efficiency. $\endgroup$ – Selene Routley Aug 29 '17 at 12:19
  • $\begingroup$ Can you shield the Geiger counter from EM with a metal screen that will let most of the X-rays through? $\endgroup$ – Keith McClary Aug 30 '17 at 1:27
  • $\begingroup$ Good idea, I was also wondering that if the geiger counter is entirely covered with aluminum foil , it might annihilate any effect of the static interference as it would serve as a Faraday cage , right? The geiger counter only shows an anomalous response when it is about 5 cm away from the tesla coil or closer, no response is recorded if it's farther away. $\endgroup$ – Chemistry4all Aug 30 '17 at 14:37
  • $\begingroup$ And regarding the amperage created by the secondary coil, it is ridiculously small, I mean you can even touch the discharge and you don´t feel almost anything , so it´s really small.So maybe although they should be produced there are not enough events per unit of time ? $\endgroup$ – Chemistry4all Aug 30 '17 at 14:38

At least in your case, it can "safely" be stated that your tube does not generate (measurable) x-rays!

This conclusion is a direct result of your 3rd point "... similar response... (even if the vacuum tube is not connected)." But if you really want to make sure, you could use two pieces of very sensitive photographic film. One gets exposed (for an hour) to the tube light and not the other (both of course, are protected from any other exposure). Comparing the two films (after developing them) will tell you if your tube is generating X-rays.


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