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Rebuilding an x-ray tube.

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Proud Mary

Mon May 14 2012, 03:39PM

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

plazmatron wrote ...

My interest after this rebuild, is centred on carbon fibre cathodes, and low kvp (1-3kvp) radiography.

Great stuff! At 2 keV, only one in two photons setting out on a journey of 10 mm through the air will arrive at their destination!

plazmatron

Mon May 14 2012, 05:05PM

Registered Member #1134 Joined: Tue Nov 20 2007, 04:39PM
Location: Bonnie Scotland
Posts: 351

Proud Mary wrote ...

plazmatron wrote ...

My interest after this rebuild, is centred on carbon fibre cathodes, and low kvp (1-3kvp) radiography.

Great stuff! At 2 keV, only one in two photons setting out on a journey of 10 mm through the air will arrive at their destination!

Quite a loss! But there is no prerequisite for a small radiographic subject to be in air. I'm sure a small subject and film container at reduced pressure could be fabricated.
In fact at these levels, I would go so far as to say such a chamber would be a necessity, since if you went by the 'sledgehammer approach' and just built a very powerful source, I am sure the resultant scatter in air would be horrendous.

I'm sure it will be a far more technically challenging project than this one has been!

Les

Proud Mary

Mon May 14 2012, 06:14PM

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

I was just being conversational, Les; it's not something I'd have expected you not to know.

Biological specimens - amoeba, for example - still require a window, so I've been reading around silicon nitride for use below 1.5 keV, but haven't found anything that looks accessible yet.

plazmatron

Mon May 14 2012, 09:31PM

Registered Member #1134 Joined: Tue Nov 20 2007, 04:39PM
Location: Bonnie Scotland
Posts: 351

Proud Mary wrote ...

I was just being conversational, Les; it's not something I'd have expected you not to know.

Biological specimens - amoeba, for example - still require a window, so I've been reading around silicon nitride for use below 1.5 keV, but haven't found anything that looks accessible yet.

So was I

More for the benefit of people that might stumble upon this thread.

Yes, I was thinking of common plastics. Commercially, for such applications, they use Polyethylene naphthalate, supported on a wire grid. As I recall, it transmits reasonably down to 100eV or so.

I see no reason why, polypropylene, polyethylene, cellulose acetate etc, couldn't be fashioned into an x-ray window. Even if the plastic is somewhat permeable, on a fast enough continuously pumped system, I don't see it being too much of an issue.

What do you reckon?

Les

Proud Mary

Tue May 15 2012, 09:51AM

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

I see polyethylene naphthalate being used for X-ray detector windows here:

As with the well known Kapton (C22H10N205) windows, I imagine their suitability would depend on whether the absorption edges and X-ray fluorescence of elements in the window could interfere with whatever outcome you are hoping for.

Clearly, slight permeability and outgassing of polymer windows isn't important under continuous pumping in a demountable source, and what's more, abundant ultra soft rays can be produced in glow discharges at relatively high pressures (e.g. Aluminium KÎ± (1.5keV), in He at 200 millitorr, anode 2 kV.)

As for the silicon nitride windows I foolishly suggested...

"A further problem with the contact method for producing soft x-ray images has been that the ($350 - Stella) silicon nitride windows rarely, if ever, survive the imaging process..."*

*A.D. Stead et al. Soft x-ray contact microscopy of biological specimens: Aluminum-coated silicon nitride windows as XUV filters J. X-Ray Science and Technology Vol. 2, Issue 3, Sept.1990, pp. 172â€“179

plazmatron

Tue May 15 2012, 09:06PM

Registered Member #1134 Joined: Tue Nov 20 2007, 04:39PM
Location: Bonnie Scotland
Posts: 351

Proud Mary wrote ...

.......................... and what's more, abundant ultra soft rays can be produced in glow discharges at relatively high pressures (e.g. Aluminium KÎ± (1.5keV), in He at 200 millitorr, anode 2 kV.)

I think I have a bunch of .pdf's you pointed me too regarding that. A He discharge seems particularly attractive, since it is so inexpensive and readily available, and pressure favours even a small displacement pump, for the vacuum.:-D

As I recall, weren't some of those x-ray tubes made entirely of plastic?

Les

Proud Mary

Tue May 15 2012, 11:07PM

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

plazmatron wrote ...

This one's a real cracker, and you'll see at once how this very simple set-up can be modified, adjusted, and re-invented, as far as scientific imagination can take you:

Kuichi Tsuji and Kasuaki Wagatsuma Compact Glow Discharge X-ray Tube Review of Scientific Instruments Vol 69, No. 11, Nov. 1998

I haven't been able to look at the full text of this next one from the same guys, but the abstract alone will be enough to guide you as there is a lot of literature about the Grimm glow discharge lamp. Note the report of strong continuous as well as characteristic emission at up to 5 kV.

Jpn. J. Appl. Phys. 36 (1997) pp. L446-L448

Fast Electrons from Grimm Glow Discharge Helium Plasmas

Kouichi Tsuji, Hideyuki Matsuta and Kazuaki Wagatsuma

Pulsed high voltages with a maximum of 5 kV were applied to the Grimm glow discharge lamp using helium gas. Strong radiation of the continuous X-rays and the characteristic X-rays from the window materials of Al and Zr thin films was observed. We consider that the high-energy electron, namely, the runaway electron, emitted from the cathode surface passed right through the hollow anode and bombarded the X-ray window, resulting in the X-ray emission. This electric discharge lamp is expected to be useful as a new electron and soft-X-ray source.

Finally, here's a good general view of the Grimm thing:

Bogaerts, A. and Gijbels, R. Comprehensive Description of a Grimm-type glow discharge source etc Spectrochimica Acta Part B 53 (1998) pp. 437 -462

I use an old 2250-0-2250 350 mA transmitter HT transformer in my experiments using a variac on the primary side to set the output voltage. This is followed by a bridge rectifier using MW oven diodes, and the usual reservoir and smoothing capacitors together with monster choke of the thermionic era. I used this approach because I had all the parts knocking around - I'm always discovering things I didn't know I had - but there must be much more modern ways of producing a stiff but variable 1.5 - 5.0 kV DC supply of a few hundred mA without having to burgle a museum.

Stella

Proud Mary

Wed May 16 2012, 04:12PM

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

Les, here is the paper which uses the plastic body of a syringe as the chamber for a soft X-ray source:

Murakami H, Ono R, Hirai A, Hosokawa Y, Kawai J. A simple X-ray emitter. Anal Sci. 2005 Jul;21(7):881-4.

plazmatron

Thu May 17 2012, 12:11PM

Registered Member #1134 Joined: Tue Nov 20 2007, 04:39PM
Location: Bonnie Scotland
Posts: 351

Yes, those are they! Thanks!

It is interesting, that no commercial application seems to have come of these!

Thinking about it, I would be interested to see, how 'bright' a source could be created based on these with nanosecond high current pulses...........

Proud Mary

Thu May 17 2012, 01:58PM

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

plazmatron wrote ...

Yes, those are they! Thanks!

It is interesting, that no commercial application seems to have come of these!

Jun Kawai, Hideshi Ishii, and Yoshinori Hosokawa Terasawa-type small X-Ray Gas Tubes and its Application to Neutralizer for Static Electricity XXIInd Int. Symp. on Discharges and Electrical Insulation in Vacuum Matsue, 2006

This paper looks a bit dodgy to me, Les.

"DC electric potential of from 500 V to 2 kV were applied, ... (and)... X-rays were observed by a Geiger-MÃ¼ller counter." I suppose some of the 2 keV photons will have have transited the Kapton window, and heroically struggled through what would have to be a very short air gap - but then they would have to get through the end window or wall of the GM tube, and still have enough puff left to do some ionising when once they got inside. It just doesn't look right, does it? Elsewhere in the paper, and in the abstract, mention is made of 5 kV, but even here no one familiar with the ineffable mystery of the ultra-soft rays would ever think of using a GM tube to detect them. It is, of course, a paper translated from the Japanese, and the translator may have misused the term "Geiger-MÃ¼ller counter" as a generic for all radiation detectors, but it certainly raises a question mark, doesn't it?

There are also patents for glow-discharge X-ray sources proposing their use in food sterilization &c. e.g.

but as you know, the existence of a US patent is no guarantee that something will work, or ever has done!

Stella

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