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Vacuum Rectifiers X-rays report

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radhoo

Mon Jan 17 2011, 02:06PM

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

05.A Field distribution test
Note: A 2X2 Tube in inverse polarization at 50KV, placed with the anode towards the fluorescent screen (perpendicular on the screen's surface):

Distance between tube end and screen: 3cm .

Comments: if the central black spot is probably a shadow caused by the metallic anode cap, then what is the bigger concentric shadow ring?

radhoo

Mon Jan 17 2011, 02:32PM

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

I already said that IMO the CCDs + fluorescent screens offer a great potential in detecting and dosing the X-rays. Here's the last image again, with two levels of segmentation (threshold) applied. In image processing, threshold is a segmentation process in which only the pixels with a high enough intensity pass (bigger then the configured threshold) and are market as white, the others are market as black.
So by adjusting the threshold it is possible to observe the more intense spots as captured by the digital camera. This not only shows where the field is more intense, but it also helps in observing the distribution field. As stated previously, a needed next step is to enclose the tube totally in Fluorescent material, and to record a 360 degrees image.
With the image above, it is possible to observe the tube has a stronger emission in the left half, then it has in the right one as per the presented position:

Central picture shows the area with the most intense emission.

Proud Mary

Mon Jan 17 2011, 03:07PM

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

radhoo wrote ...

04.Some measurements

I don't think it right to call any of these indications 'measurements.' You have used equipment which you knew to be unsuited to the measurement of X-rays below 50keV, and now you ask why the indications on these useless instruments are all in disagreement.

The best use for the yellow brick with the handle on it? Paint it black and use it as a weight for eel fishing in the DunÄƒrea.

radhoo

Mon Jan 17 2011, 03:32PM

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

Proud Mary wrote ...

I don't think it right to call any of these indications 'measurements.' You have used equipment which you knew to be unsuited to the measurement of X-rays below 50keV, and now you ask why the indications on these useless instruments are all in disagreement.
The best use for the yellow brick with the handle on it? Paint it black and use it as a weight for eel fishing in the DunÄƒrea.

Besides the saturation in close proximity of the tube, I had some good use of the RD1706: Moving it further allowed this detector/indicator to function a little better: By doing so, the RD1706 showed an expected lower radiation level, as per the distance increment. It also has a very loud beep that goes on as soon as I power the tube which is also useful as a warning.
Even if the indications are totally inaccurate, the values indicated are related to the distance, so I can at least see where the field is not so hot/active/counts producing.

Proud Mary

Mon Jan 17 2011, 03:49PM

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

I think these experiments mapping the X-ray emission lobes of the 2X2 are both new and excellent, but you must sort out your dosimetry and shielding issues or your fingers will turn into bratwurst, my friend:

radhoo

Mon Jan 17 2011, 04:19PM

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

A bit offtopic but,

All tests are performed remotely. Basically the setup is in a different room, 6 meters from where I am, two walls in between, one of them made of concrete and steel 15cm tick. So my fingers should stay safe. If there was a such a risk, I would never run these tests.

Proud Mary

Tue Jan 18 2011, 04:02PM

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

Those bratwurst do look good, don't they?

Thinking about the concentric shadow surrounding the anode shadow in your radiograph, I wonder if it can be the longitudinal shadow of the anode bell from X-ray photons produced by field electron impacts on the circular shielding plate?

It certainly is an interesting feature worth investigating. If you have a good magnet, and place it near the shielding plate it might cause sufficient disturbance of the field emission electrons to show up on the radiograph

radhoo

Tue Jan 18 2011, 05:42PM

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

I have a few Neodymium n48 magnets, that I can use for this purpose. Probably this evening I will run some more tests.

Some other ideas:
- re-test my NaI scintillation probe with this x-ray emitting setup
- try to identify a correlation between photon energy and : 1) pixel intensity in camera images -or- 2) scintillation amplitude (in an effort to get the dosimetry on the right direction) . There are issues with both I will see what I can come up with.
- test some other vacuum rectifier tubes (I got a few, hope there are some without lead glass as well).
- use aluminum foil for hardening the beam and see how that works .

Interesting to see how well the lead-glass works for shielding! See the 03.6LJ6A above.

Arcstarter

Tue Jan 18 2011, 08:50PM

Registered Member #1225 Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253

Great thread, Radu! This thread will be priceless for the project i am working on, which is an experimental x-ray machine like yours, with a high voltage stabilizer. I would like to get some rectifier tubes and test them as you did, too. Also, i have newfound motivation for the project, i think i'd like to go melt some lead now

Good luck!

Proud Mary

Tue Jan 18 2011, 09:09PM

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

If the 2X2 anode is made of molybdenum or nickel - which is quite probable - you will see one of the reasons why the X-ray output in the 'normal' tube polarity is so weak.

With a Mo anode, the bremsstrahlung is not plentiful, and the KÎ± emission only just on the edge of possible transmission through the glass.

And if the anode is nickel, the KÎ± emission won't even get through the glass envelope:

Notice that there is no photon emission at all between about 40keV and 55keV for either metal - a very common phenomenon.

If we believe the worst of Cold War propaganda, and imagine that these Soviet 2X2s had an anode made from old scrap iron, we have
the same picture:

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