Mystery propably X Ray tube thing

[Da_Stier]

Hi all,

a few years after graduating from school, I got a call from my physics teacher, telling me that they renovate the physics room and that I can come and get some stuff if I want to.
So one thing I got was this interesting tube thing, mainly because it said "Verwendung untersagt" basically meaning "use prohibited".
My teacher said, she doesn't really know what it is supposed to be used for and that it was there when she came to the school twenty years earlier.

The tube is around 30cm long and around 3cm in diameter. One electrode is a flat plate, one is a cylinder.









When powering it with DC from a Flyback transformer, it has this beautiful bright green glow and emits enough X-rays, that the geiger counter goes crazy.



I only went there for a second to take a single picture, since I don't want to get to much of these X-rays to be honest.
Judging by the colour, it does not seem to be a simple noble gas tube?

Does anyone know what such a tube would be used for or is it just an educational thing from a time where X-rays at school were acceptable? 



Greetings,
Michael

[johnf]

Looks like a Townsend discharge tube not an x-ray tube.
These were used to measure high voltage characteristics in both AC / DC mode
with your Geiger counter that close the rf field from the tube might be making the counter go berserk
What actual voltage is the flyback??

[Da_Stier]

Thanks John,

very interesting, I never heard of such a thing, fascinating stuff.
You are propably right about the geiger counter, it is affected up to around 35cm or around a foot from the tube.

The flyback is a TV flyback with a simple ZVS driver.
I'm not sure about the actual voltage but I would guess around 25 kV maybe.
.... much to low for an actual X-ray tube, I know that much.   





Greetings,
Michael

[Mads Barnkob]

Please do use a insulated rod / chicken stick and not just holding a alligator test clip on 25 kV! 

[Da_Stier]

Thanks Mads,

yes that was a pretty careless thing to do, sorry.
I "optimized" the picture a bit, so that I'm not a bad influence to anyone. 



Greetings,
Michael

[Duane B]

If that green glow is on the inside surface of the glass, and not in the middle of the tube, then the green glow is most likely produced by x-rays. I think that is an antique demonstration tube for hooking up to an induction coil. It looks similar to a cold-cathode flash x-ray tube but I think this tube pre-dates the flash x-ray tubes.

This tube reminds me of an article I read in an old book a long time ago that told about making your own x-rays. It said to take an old radio vacuum tube from the 1920s, coat the outside glass with tinfoil, and connect an induction coil between the tinfoil and the pins on the bottom of the tube. If x-rays were produced you would see a green glow on the inside surface of the glass. I tried it and it did work. Be careful with that tube because I think it is indeed making x-rays.

[huntergroundmind]

I have similiar tubes. When I aquired them, 5 pieces were placed inside wooden holder  Each tube had sticker with value of pressure. They were used to demonstrate glow discharge at different pressures, by connecting to induction coil. One of them had pressure sufficiently low to produce x rays. Unfortunately wooden base was rotten and moldy, and one tube was cracked, so I have only 4.

[Patrick]

very interesting, I never heard of such a thing, fascinating stuff.
You are propably right about the geiger counter, it is affected up to around 35cm or around a foot from the tube.

Generally here at the lab we're told to hold the meter 30 cm away from the source, full arm extended with your upper body sort of away from the source. This keeps your exposure down and 30 cm is generally a common standard to control for "inverse square law". I wouldn't be surprised if, as said before, that RFI/EMI played a roll in causing some bogus clicks and that dropped off with distance too. So I'd believe the 30 cm measurement more.