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Vacuum Rectifiers X-rays report

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radhoo
Sat Jan 15 2011, 11:20PM Print View
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Location: Romania
Posts: 698
See the following posts for the lastest results. Here is just a quick insight of the current status:

Photo 1: 2X2 tube, inverse polarization (HV+ to Tube pins, HV- to Anode) 50KV, 15 s exposure, f/3.5, ISO 100.
Photo 2: same, different setup
Photo 3: determining the x-ray distribution field test

Photo 1&2: The same remote control while being illuminated by the 2X2
Photo 3: SDCard

Comments: For this thread I will be using various vacuum rectifier tubes, for the purpose of checking the X-Ray emission in cases of over-voltage. I will try to indicate the field distribution, best angles, and other details, but these take a lot of time, so this thread is work under progress.
Each of my experiments will be indexed like 01, 02, etc. I will also indicate the tube used, the voltage level, whether it was connected in normal polarization (meaning the Supply HV+ goes to tubes Anode) or inverse polarization (HV+ goes to the tube's bottom pins, connected together, and HV- goes to the Tube's anode). Also photography details such as fluorescent screen type, camera, exposure times, will be indicated.
Safety: There will be an entire post dedicated to safety below, however I should point out that all my tests are performed remotely, and the camera is set on a tripod, with a timer. I also use a few dosimeters to at least indicate the presence of x-rays, since they are not well suited for dosing the emission: Radex 1706 (30keV minimum sensitivity), Terra-P, Kvarts DRSB01, CDV 700.
Power supply : I'm currently using my DIY 50KV Variable supply: (ZVS+Multiplier in paraffin). For all the tests below, unless otherwise indicated, the complete system is powered from a regulated variable DC supply ( ), currently set at 12V (20amps max). Very little power , this could easily run on battery!

01.First Tests
Note: This first test uses a 2X2 connected in normal polarization.
Objective 1: demonstrate x-ray emission.
Objective 2: Verify the x-ray level is suitable for photography

Thanks for Proud Mary for discussing the characteristics of the 2x2 Russian rectifier:

I recently acquired a few of these tubes, so I run a few tests of over-volting them using my 50KV supply:

The system was triggered remotely, from safe distance (more then 6 meters) with concrete walls in between. The camera used to capture the results is a Canon S2 IS, operated using the timer function. The camera was set on a tripod, at 1.5meters away from the 2X2, and the zoom set to maximum. Focus was set to manual.

For these first tests, a limiting resistor was added in series with the supply. The tube's anode was connected to positive.
A Radex 1706 dosimeter, set in close proximity of the tube (15cm), indicated more the 800uSv/h in just 3 seconds of operation. At aprox. 80cm, the value dropped to 200uSv/h (Background level 0.13uSv/h). At two meters, the Radex was still detecting a high level. The datasheet of this dosimeter indicates it is capable of detecting X-rays of minimum 30keV.

The purpose of these tests was to determine if a radiography is at least possible using this setup. Fluorescent screens of 4 different types where used:
1. A first test, to see if the fluorescent screen emits any light:

8 seconds exposure, f/3.5 (not so good camera), ISO 400 (very noisy on this camera).

2. An object (a remote control) was added between the 2X2 and the fluorescent screen. For all the pictures here, the fluorescent screen was placed immediately after the remote control, and the distance from the tube was 5-8cm:

Exposure: 10s , f/3.5, ISO 400 , Green emitting fluorescent screen 1 (will add type later)

3. Using a blue emitting fluorescent screen:

Exposure: 10s , f/3.5, ISO 400 (Bad, bad camera).

4.Another one:

Exposure: 15s , f/3.5, ISO 400

TODO:
- a lot!
- build a container for the 2x2, filled with oil for cooling, since the tube is getting quite hot even if operated for only a few seconds
- try the tube with reversed polarity
- use lead sheet over the oil container and tube, with a small orifice to control the emission geometry
- place a micro-ampmeter in series with this setup
- dare to use the DSLR for a few shots? or maybe not.
- measure the radiation levels, in relation with the distance - estimate the safety levels
- build a few more detectors
- or -
put all the setup in a lead box.
- get a better x-ray tube
- is there anything else? comments? thanks!
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radhoo
Sun Jan 16 2011, 10:55AM
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[-]
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Proud Mary
Sun Jan 16 2011, 11:32AM
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If the figure of 800 μSv/h at 15cm is roughly correct, and you do have 50kV on the diode anode, then the field emission current through the 2X2 is much less than 1μA.

The X-ray energy response of GM tubes below 100keV is very non-linear, so your actual dose rate may be smaller than this. It says a lot for the intensifying screen that it is able to function with such low fluence.

You may be able to influence the electron stream with one or more strong external magnets, and so give the beam better directional properties.

The image curvature or convexity at the upper edge shows the shadow the anode bell very clearly, as I showed you some weeks ago in a diagram.

I am intrigued by the fate of electrons hitting the very edge of the anode bell at a 'grazing' incidence.

PS Added Later. Don't forget you can use an ordinary mechanic's feeler gauge set as a penetrameter, or use strips of ordinary kitchen aluminium foil in layers if your rays are too soft even for the thinnest of the steel feeler gauges.
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vircator
Sun Jan 16 2011, 03:39PM
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Can you point us to a source for the Fluorescent screens you used? Thanks
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radhoo
Sun Jan 16 2011, 03:58PM
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vircator wrote ...

Can you point us to a source for the Fluorescent screens you used? Thanks

They were taken out of X-ray cassettes. You can find them on Ebay or maybe you have a friend doctor (thanks vasil).
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radhoo
Mon Jan 17 2011, 12:17AM
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02.Experiment inverse polarization
Note: Tube used 2X2. The tube was position at a very small angle from the screen plan normal, at a distance of 4cm.
Objective: compare the normal polarization emission with inverse polarization


The first image was taken with the 2X2 tube powered by connecting HV+ to Anode. The second picture has the connections reversed, the 2X2 has the anode connected to HV- , and the bottom pins connected together to HV+. The difference is obvious.


So using this reversed connection, here are some results:




The quality is good enough to actually use this radiograph for seeing the internals. A very cheap solution for a reasonably good image.

The 2X2 gets hot very quickly, the 15seconds needed for camera exposure are the maximum I would go for. Putting it under oil would improve this issue.
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Wolfram
Mon Jan 17 2011, 07:42AM

Joined: Sat Feb 04 2006, 01:31PM
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That's not bad at all. It's the best result I've seen from operating a rectifier tube in cold cathode mode.
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radhoo
Mon Jan 17 2011, 12:06PM
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Anders M. wrote ...

That's not bad at all. It's the best result I've seen from operating a rectifier tube in cold cathode mode.

Thank you, Anders M., I can only take your words as an encouragement to move further.

Here is the last radiograph, with the exposure/gamma/brightness adjusted by software:


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radhoo
Mon Jan 17 2011, 12:40PM
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03.6LJ6A (lead glass)
Note: n/a
Objective: Use a 6LJ6A shunt with Lead Glass in inverse polarization setup with the 50KV source and check the x-ray emission as recorded by the camera . No dosimeter data available here.

Result: No emission -or- emission too weak.
The two objects are seen on the fluorescent screen, only as shadows, from the UV light generated inside the tube.
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radhoo
Mon Jan 17 2011, 01:05PM
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04.Some "measurements"
Note: Tube 2X2 in normal polarization at 50KV.
While waiting for a proper lead box to encapsulate this x-ray machine, here are some measurements. Unfortunately they seem to be quite unreliable. I might say that the best detector at this point, seems to be the fluorescent screen+camera. One of my new tests will be a box made of fluorescent screens, with tube placed inside, to be a better idea of the field distribution and intensity.




These devices are not suited for dosing the X-Rays, they might work for detecting them, but might not work at all. So they have to be considered unreliable.
Picture 1: Radex 1706 and Terra-P Geiger Counters at 30 cm . The Radex seems to get saturated very quickly.
Picture 2: A CDV 700 Geiger counter set to x100 Scale.
Picture 3: A CDV 717 Ionisation chamber detector, set to x0.1 Scale, and placed at 15cm from 2X2.
Picture 4: The Radex 1706 at 50cm going for saturation
Picture 5: A 100uAmpmeter connected in series, goes past scale. Note the circuit is as follows:
(-)Bipolar HV Supply 50KV (+) ----> HV Limiting resistor ----> 2X2 Tube anode
|
|------> 100uAmpmeter--------------------------------> 2X2 Bottom pins together.


Could use some suggestions here. Thanks!
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radhoo
Mon Jan 17 2011, 02:06PM
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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?

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radhoo
Mon Jan 17 2011, 02:32PM
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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.
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Proud Mary
Mon Jan 17 2011, 03:07PM
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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 Dunărea.
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radhoo
Mon Jan 17 2011, 03:32PM
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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 Dunărea.

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.
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Proud Mary
Mon Jan 17 2011, 03:49PM
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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:



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radhoo
Mon Jan 17 2011, 04:19PM
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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.
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Proud Mary
Tue Jan 18 2011, 04:02PM
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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

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radhoo
Tue Jan 18 2011, 05:42PM
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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.
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Arcstarter
Tue Jan 18 2011, 08:50PM
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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!
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Proud Mary
Tue Jan 18 2011, 09:09PM
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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 Kα emission only just on the edge of possible transmission through the glass.





And if the anode is nickel, the Kα 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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radhoo
Wed Jan 19 2011, 09:32AM
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@Arcstarter, thanks, make sure those stabilizers you're planning to use don't have lead glass. I was surprised to see how efficient they are in blocking my 50keV x-rays.

@Proud Mary, There is iron inside, I saw this when doing the neodymium magnets test, not sure if it's the entire anode bell - but I don't think so, since the attraction was weak - probably I was sensing just the steel wires holding the internals together. Do you perhaps have another chart showing the emissions for tungsten? Got something here: , this sure explains the big difference in choosing the anode.
For inverse polarization, I wonder how quickly the filament will get destroyed after these tests. And I'm guessing the electrons have one single favorite spot.

Time to post some new results, I got the field distribution shape, and it looks very good!
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radhoo
Wed Jan 19 2011, 11:22AM
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06.A Field distribution test
Note: A 2X2 Tube in inverse polarization at 50KV. Setup looks like this:


Test1: The Z(vertical) axis:

Here is the last image again, with exposure/brightness increased in software:

Conclusion: As expected, on the vertical axis, the radiation is higher at the same level the anode is (the tungsten filament, under the bell). The bell doesn't make any difference, in fact the radiation is higher where the bell is (it passes straight through).

Test 2: First 360° (X/Y) distribution results
The same setup was used and four images of the fluorescent screen where taken with tube at A=0° , A=90°, A=180°, A=270°. Distance from the tube was D=6 cm (another test with D=10cm was performed, but with the same results).
It was very important not to move the camera at all , not to change any distances, fluorescent screen position, etc, so the results would be comparable. Here are the 4 shots, with exposure/brightness improvement:

And after Segmentation Threshold was applied (Level=140):

Here's is the tube, at 0°,90°,180°,270° in the same positions used to generate the images above:

Conclusions:The field distribution is uniform. The small changes in shape are only caused by the small metal plate, under the bell (easily visible by comparing the tube images with the blue fluorescent images). The source of radiation resulting from the 2X2 tube, should be visualized as a HOT, vertical rod, places inside the Bell. This rod, is , of course, the tungsten filament positioned vertically. The metallic bell produces almost no perturbation on the x-ray escaping it, however the small metal plate, under the bell is a strong blocker (it is not steel! what metal could that be?)
LE: the reason we get less radiation under the bell level is not entirely related to the small metallic plate, but also to the electric field distribution that causes the X-ray emissions: The electrons move from the bell to the inner tungsten filament, and produce x-rays, so we only get them between the bell and the internal filament. The metallic plate only blocks/attenuates a small ammount of rays that are oriented to the bottom of the tube. Most of them however are emitted perpendicular on the filament direction. X-RAY emission is therefore distributed like this:

The blue arrows are the electron paths, and the greens are the photons emitted. The internal filament represented in red is connected to HV+ and the external bell is connected to HV-.

Test 3: Another approach to 360° (X/Y) field distribution verification
A simpler test was performed, by surrounding the 2X2 with a tube made out of fluorescent material. Some extra attention was payed to keeping the 2X2 as close a possible to the center of the outer tube:


Segmentation on the fluorescent screen images:

A very nice cylindrical,uniform emission field! The projected band appears to be quite narrow, related to the size of the vertical tungsten filament inside the tube. The picture to the right was added to observe the position of the tube elements as compared to the fluorescence projected on the intensifier screen.

This nice emission field can be used to project good quality radiographs, using this very cheap vacuum tube - the 2X2 .
The only concern is that the emission is radial (cylindrical shape with the center in the tungsten filament) but with some geometry knowledge unaltered, flat projections, can be obtained.
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Proud Mary
Wed Jan 19 2011, 11:24AM
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X-ray production efficiency is roughly kV x Z x 10E-6, where Z is the Atomic Number - 74 in the case of W.

For an anode voltage less than 69.5 kV, there can be no K-characteristic radiation from a tungsten target, as the incident electron energy must exceed the K-shell binding energy for emission to occur.







This paper contains some very interesting observations on W target emission:

Soole BW The Attenuation of X-Radiation Generated at Constant Potentials Sufficient to Excite K-Radiation in a Tungsten Target Phys. Med. Biol., 1971, Vol. 16, No. 3, 427-437



But let's not jump to conclusions that the emission comes from W! Certainly the heater filaments will be either W, or a W/Mo alloy, but there are other metals besides in the construction of the valve.

Edit: You were posting yours above, while I was writing this.

You have made a very good job of this Radhu. Excellent!
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radhoo
Wed Jan 19 2011, 11:39AM
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07.Magnetic field influence
Note: A 2X2 Tube in inverse polarization at 50KV. A very strong Neodymium magnet was placed outside the tube, right next to the bell:

I took three pictures:
1) with the north pole of the magnet set towards the tube
2) without magnet
3) with the south pole of the magnet oriented towards the tube
The results:

Now the threshold (L=150):

In this setup, the magnet produces no visible influence on the emission field.

I am quite pleased of this method of highlighting the results by using image processing on the fluorescent screen shots. It shows a great potential of observing the x-ray phenomenon in more detail. Segmentation can be binary, as used up until now in my reports, but it can use several threshold levels and multiple colors to indicate various radiation levels. The following example shows two segmentation levels of 180 , corresponding to very intense radiation, and 140, corresponding to a decrease in radiation level:

An entire scale of intensities can be built this way with a corresponding color map legend.
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Proud Mary
Wed Jan 19 2011, 11:52AM
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I feel you should try the magnet experiment again, with the magnets lower down so the magnetic field bisects the open end of the anode bell and the electrode connection leads, where electron field emission is likely to be occurring.

There will be almost no electrons available for interaction with the magnetic field as you show it in the set-up in the picture. The anode bell will shield any electrons flying around inside from the magnetic field.



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radhoo
Wed Jan 19 2011, 12:00PM
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I also need to see the angle at which the narrow emission band expands with distance. This one:

To determine that I will use two fluorescent screen cylinders at a few cm apart.

LE: I will also write a little software to do the segmentation automatically and create a map of colors. If I knew the Fluorescent screen fluorescence coefficient (must be something related to the energy of incident x-ray photon and the amount of visible light emitted), I could link it to the light intensity and compute the x-ray energy of the color map areas.The fluorescence surface would indicate the counts. That would a neat x-ray dosimeter. Eg:

Doing the same thing, but using several camera-captured frames, at a well known time interval, allows the time component to jump in the equation, so the Sv/h can be computed for a given color-map area.
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Proud Mary
Wed Jan 19 2011, 12:13PM
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Radhu, if you use the shadow of a metal washer, you can easily plot the beam divergence, by measuring the amount the washer's circular shadow expands with distance from the valve.

You can also assess the quality of the beam by means of a metal gauze or grill with square holes. Distortion of the squares imaged directly relates to field non-linearity.

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radhoo
Wed Jan 19 2011, 12:15PM
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Indeed, geometry offers endless possibilities to solving a problem.


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Proud Mary
Wed Jan 19 2011, 12:22PM
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I added this to my post above whilst you were posting yours:

You can also assess the quality of the beam by means of a metal gauze or grill with square holes. Distortion of the imaged squares directly relates to field non-linearity.
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radhoo
Thu Jan 20 2011, 11:13PM
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Location: Romania
Posts: 698
Unfortunately I couldn't find such a metal piece with square holes. I'll see if I find something else. Some more interesting finds are to follow, meanwhile, here are some radiographs I took:

SDCard:


Mogo Bluetooth mouse ( it has a metallic side):


A piece of coral - blocks the rays completely!


The Kvarts DRSB-01 Dosimeter


As can be seen in the pictures, the optimal position of the tube is at 45 degrees, with the anode towards the fluorescent screen. This way a maximum uniform illumination surface is obtained (see the nice big square green glow with uniform intensity - less shadows). More on this in the next post.
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