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Proud Mary

Fri Jan 21 2011, 03:04PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Ah, the benefits of a wide interest in general science!

Some of those mineral specimens are sure to fluoresce.

Proud Mary

Fri Jan 21 2011, 05:40PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Radhu, I found a box of 2X2As under the stairs, so have sacrificed one to get a decent image of the cathode assembly for you. Comparing this with your angle plot, the rays may well be coming from the oxide cathode.

The misalignment of the cathode occurred while breaking the glass.

1295631260 543 FT0 Russian 2x2a Cathode Assembly 1

1295631293 543 FT0 Russian 2x2a Cathode Assembly 2

The anode bell is strongly attracted to a magnet - perhaps a nickel alloy. The screening disk is also magnetic.

EDIT: I've thought about what I have called a 'screening disk' and now think it is a heat shield to protect the glass seals from radiant heat.
In an amplifier, one would think of it being an EMI shield, but not in a diode power rectifier like 2X2. The bright reflective surface of the disk supports this interpretation.

radhoo

Tue Jan 25 2011, 12:47PM

Registered Member #1938 Joined: Sun Jan 25 2009, 12:44PM
Location: Romania
Posts: 701

Well, one way or another, that disk is making the lower part of the x-ray emitting 2X2 useless. But even so, this tube is great.

Thanks for sharing those nice pictures. Here is one with the tube in operation, showing the hot, glowing "cathode" caused by electron bombardment (that sounded very SciFi-ish):

I had little luck with my minerals, I tried a different pack containing mostly quartz based stones, polished nicely in sphere shapes, but will try the one posted above as well:

radhoo

Tue Jan 25 2011, 12:51PM

Registered Member #1938 Joined: Sun Jan 25 2009, 12:44PM
Location: Romania
Posts: 701

and while the tube is glowing inside , here are some outside results:

First picture: an audio system IR remote while illuminated by the 2X2 tube
Second picture: a hardware password key
Third: a camera IR remote

I might be able to increase the voltage even further, and run some other tests, if I make a lead box first:

Proud Mary

Tue Jan 25 2011, 02:44PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

radhoo wrote ...

I might be able to increase the voltage even further, and run some other tests, if I make a lead box first:

Did you think to wonder when in history the lead shielding Recommendations of the Second International Congress of Radiology were made, Radu?

You can read all about it in the crumbling, yellowed pages of The British Journal of Radiology (1928) 1, 30

I am not saying it is necessarily wrong, but that data of such vintage must be carefully evaluated before putting it to any practical purpose. For example, no duration of exposure is given, a serious omission. Standards of radiological protection have changed dramatically for the better in the last eighty years.

There is an on-line X-ray shielding calculator for lead and other common materials run by the University of Dundee here:

There is a Constant Potential X-Ray Device Dose-Rate and Shielding Calculator at the RadPro site here:

and a dose-rate/distance Inverse Square Law calculator here:

Edit: Afterword on Fluorescent Minerals

Minerals which fluoresce with short wave UV will often fluoresce with X-rays.

This table distinguishes between short wave and long wave UV induced fluorescence:

Mineral UV Fluorescence Colors - Summary Chart is here:

radhoo

Tue Jan 25 2011, 06:42PM

Registered Member #1938 Joined: Sun Jan 25 2009, 12:44PM
Location: Romania
Posts: 701

I will try some uranium glass that puts out a very strong greenish fluorescence under UV light, making sure I block all visible/UV light from the tube with a piece of aluminum foil.

Proud Mary

Tue Jan 25 2011, 07:11PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

radhoo wrote ...

I will try some uranium glass that puts out a very strong greenish fluorescence under UV light, making sure I block all visible/UV light from the tube with a piece of aluminum foil.

Black card, and heavy black paper of the type called 'cartridge paper,' can be bought from artists' materials shops, and are both very useful in this sort of work. For extra light-proofing, you can use kitchen aluminium foil on the outside, and the black paper inside to reduce reflection of any light leakage left. It is worthwhile having double layers like this in photon counting experiments with photomultipliers.

Softer X-rays may not be able to penetrate the outer layer of a sample, and so produce little fluorescence even when the substance itself is in fact quite fluorescent.

The glow discharge in the 2X2 looks very interesting. When I did my 2X2 experiments, I didn't give it much thought, as I knew much less than I know now. What is it? I don't have an optical spectrometer, and don't fancy trying to use the home made DVD-type spectrometer near an X-ray source. But I have a hunch that the explanation for the plentiful X-ray emission of 2X2 compared with other popular X-ray sources - PD500, 6BK4B etc - will be found in a spectral analysis of the glow discharge.

radhoo

Wed Jan 26 2011, 11:39AM

Registered Member #1938 Joined: Sun Jan 25 2009, 12:44PM
Location: Romania
Posts: 701

I'd say that the first difference between the 2X2 and shunts like PD500, 6BK4B but also 6LJ6A etc, is the target geometry/position.

Instead of having a bottom, small sized filament, the 2X2 comes with an inner, rod like, central / very conveniently placed filament, covered in that white oxide that seems to help a lot - I believe the following features result from this:
- uniform emission with less shadows, when placing the tube at 45degrees the resulting images are well illuminated
- no electron beam focal points that would melt/puncture the filament if it was to be struck directly

I will capture a few close-up pictures of this glow, next time I power the tube. Now that the winter is so harsh I have other electron related problems - making my diesel car start.

Proud Mary

Wed Jan 26 2011, 01:32PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

1296048141 543 FT0 Russian 2x2a Anode Bell Exterior

The external diameter of the anode bell is 20mm.

1296048175 543 FT0 Russian 2x2a Anode Bell Top View

1296048078 543 FT0 Russian 2x2a Anode Bell Interior Radu A

The very slightly elevated and rough spot welds on the inside top of the anode are a possible field emission source.

radhoo

Wed Jan 26 2011, 03:14PM

Registered Member #1938 Joined: Sun Jan 25 2009, 12:44PM
Location: Romania
Posts: 701

Great pictures.

Does it make sense to find out the anode bell's density?

With a sensitive balance the weight should be no problem. I'm not so sure about the volume, using a liquid and a small graduated container - might require cutting the anode bell in small pieces to fit a small tube. For bigger tubes would be hard to distinguish the levels difference.

Proud Mary wrote ...

The very slightly elevated and rough spot welds on the inside top of the anode are a possible field emission source.

That's a fair assumption. But shouldn't that limit the area of the new cathode that gets the electron bombardment? In a picture I took with a different purpose (posted abovE) the internal oxide rod glows intensely. Having such a tiny electron emitters I would have expected to see only the top part of the oxide rod glowing.
What happens under high vacuum anyway: Do electron jump on the shortest path, or there is a diffuse electrical field filling the space between electrodes?

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