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Registered Member #1938
Joined: Sun Jan 25 2009, 12:44PM
Location: Romania
Posts: 701
Proud Mary wrote ...
Radu, the frequency of the incident light being the same in all cases, are you saying that the magnitude of your photoelectric voltage is related to the work function of the metal surfaces - as in Einstein's photoelectric equations - and that this property can predict the X-ray performance of the tube?
Steve McConner wrote ...
So maybe Radu's method just detects whether there is any barium in the cathode/anode.
radhoo wrote ...
I will try to bring more evidence that a simple laser pointer test can indicate whether a vacuum rectifier tube is suitable for X-ray emission, given some preliminary requirements are met like: high-Z target, electrode geometry, etc . For the time I had for this evening's test, this is all I could come with.
Steve, Proud Mary, I'm not trying to guess the anode metal characteristics using light. More details follow:
I need to highlight the preliminary requirements mentioned above. I'm not saying that if a vacuum tube provides high voltages when illuminated it will also emit abundant x-rays. Instead I'm saying that high vacuum is what makes the 2X2 so special and that using the photoelectric effect we have a basic test of getting an idea of the gas pressure inside. This test should stand when comparing various rectifier tubes, that have similar metals in their internal electrodes, similar anode/cathode geometry / similar internal pressure and so on. I don't expect my Cesium-photosensitive tube to be a X-ray emitter, even if illuminated by UV produces close to 800mV!.
Actually I didn't give this much importance, until I got the Russian V1-0.1/30 . First I was delighted to see the simple internals, the large anode bell and nice spacing between the components. It also has one very sharp electrode, not connected to anything, except the bottom pin - a lot of potential for particle experiments. Then putting some light on the anode / cathode inside the bell enclosure, showed very poor photoelectric results. I had a guess this will not work well for x-rays. To support this idea I then took other tubes for a test, and DY86 was an interesting surprise.
Registered Member #1938
Joined: Sun Jan 25 2009, 12:44PM
Location: Romania
Posts: 701
That would be great if he could do it. He mentioned a vacuum rig somewhere. Les, can you go as low as 0.2mm Hg as per the article quoted by Proud Mary, describing the Hard vacuum? Do you have uranium, or at least some ore?
radhoo wrote ...
...the oxide covering the filament is either barium oxide or strontium oxide. I would assume this is barium, but Proud Mary could help me with a simple chemistry test: put a little piece of the oxide in an colorless flame: barium makes the flame green, while the strontium makes it red.
Proud Mary, could you test this for me using the broken tube's filament? An ordinary butane flame would do. Both barium and strontium are strong flame "pigments" , they have been used in fireworks, so the color should be easily visible. Barium produces a green-yellowish color, but still a green, I have some chloride somewhere, I'll see if I can take a photo for comparison.
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
radhoo wrote ...
That would be great if he could do it. He mentioned a vacuum rig somewhere. Les, can you go as low as 0.2mm Hg as per the article quoted by Proud Mary, describing the Hard vacuum? Do you have uranium, or at least some ore?
radhoo wrote ...
...the oxide covering the filament is either barium oxide or strontium oxide. I would assume this is barium, but Proud Mary could help me with a simple chemistry test: put a little piece of the oxide in an colorless flame: barium makes the flame green, while the strontium makes it red.
Proud Mary, could you test this for me using the broken tube's filament? An ordinary butane flame would do. Both barium and strontium are strong flame "pigments" , they have been used in fireworks, so the color should be easily visible. Barium produces a green-yellowish color, but still a green, I have some chloride somewhere, I'll see if I can take a photo for comparison.
I'm sure Les can pump down to a much lower gas pressure than that, if neccessary, but how low he'll have to tell you himself.
As for the colourimetric tests, Radu, do you want me to test the coated cathode cylinder, or the insulated filament inside it, as per my photomicrographs above? I will have to wait until night, to be sure of enough darkness to get a good image.
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
I'll do the flame test tonight after dinner, Radu. If the cathode coating contains strontium as well as barium, I'm not sure what colour we should expect to see with no spectroscope to separate the red from the green. But we'll find out later...
Registered Member #1667
Joined: Sat Aug 30 2008, 09:57PM
Location:
Posts: 374
Sorry for interrupting with a little question: I just bought a few DY86s for the fun of it. Has anyone tried external electrodes to affect the field inside the tube? Maybe the flashover problems can be alleviated by adding field shaping electrodes.
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
Radu I've just spent an hour looking for my other 2X2As and can't find them anywhere, though I know I have at least five, and perhaps more. I'll look for them again later, in some different crates and boxes, but if I have put them away in the wrong place, this may take some time.
Update: I have found one of them in the bottom of a box of photomultipliers, but will save it for my dosimetry experiment at the weekend. I shan't mind butchering it after that, to test the cathode coating, as I have no real use for them.
I am sorry for any disappointment my forgetfulness may have caused.
Registered Member #1134
Joined: Tue Nov 20 2007, 04:39PM
Location: Bonnie Scotland
Posts: 351
Proud Mary wrote ...
I'm sure Les can pump down to a much lower gas pressure than that, if necessary, but how low he'll have to tell you himself.
1x10e-6 torr on a good day. Way harder than the old gas discharge x-ray tubes of antiquity, and plenty hard enough to quantify any field emission characteristics.
Steve McConner wrote ...
The pinhole camera might be worth a try. The "camera" of course is simply a lead sheet with a small hole poked in it. The instructions I saw for making it were to bash an indent in the sheet with a hammer and punch, then cut/file off the little bump that appears on the other side.
That sounds like an excellent idea. I used a pinhole camera to image to focal spot of a diffraction tube, to determine the line focus windows from the spot focus windows.
I think this tube may require an image intensified setup rather than raw film to image the "anode"........runs off to shed....
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Vacuum Rectifiers X-rays report
