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radhoo

Sat Jan 15 2011, 11:20PM

Registered Member #1938 Joined: Sun Jan 25 2009, 12:44PM
Location: Romania
Posts: 699

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!

radhoo

Sun Jan 16 2011, 10:55AM

Registered Member #1938 Joined: Sun Jan 25 2009, 12:44PM
Location: Romania
Posts: 699

[-]

Proud Mary

Sun Jan 16 2011, 11:32AM

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

If the figure of 800 Î¼Sv/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 1Î¼A.

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.

vircator

Sun Jan 16 2011, 03:39PM

Registered Member #3217 Joined: Mon Sept 20 2010, 06:14AM
Location: Switzerland
Posts: 15

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

radhoo

Sun Jan 16 2011, 03:58PM

Registered Member #1938 Joined: Sun Jan 25 2009, 12:44PM
Location: Romania
Posts: 699

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).

radhoo

Mon Jan 17 2011, 12:17AM

Registered Member #1938 Joined: Sun Jan 25 2009, 12:44PM
Location: Romania
Posts: 699

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.

Wolfram

Mon Jan 17 2011, 07:42AM

Registered Member #33 Joined: Sat Feb 04 2006, 01:31PM
Location: Norway
Posts: 971

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

radhoo

Mon Jan 17 2011, 12:06PM

Registered Member #1938 Joined: Sun Jan 25 2009, 12:44PM
Location: Romania
Posts: 699

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:

radhoo

Mon Jan 17 2011, 12:40PM

Registered Member #1938 Joined: Sun Jan 25 2009, 12:44PM
Location: Romania
Posts: 699

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.

radhoo

Mon Jan 17 2011, 01:05PM

Registered Member #1938 Joined: Sun Jan 25 2009, 12:44PM
Location: Romania
Posts: 699

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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