Re: Russian 2X2 valve rectifier X-ray emission report
radhoo, Mon Dec 06 2010, 11:22AM

Sorry for re-opening an old thread, but I've just purchased some 2x2's from ebay, knowing about their regular glass and x-ray emission properties, and now I just stumbled upon this report, so thanks for the excellent details, Proud Mary.

What I'm trying to do is to use my CW multiplier to drive a rectifier tube to a level where it can impress my intensifier screens, enough to be captured by a digital camera.

I also have the 6LJ6A, 3CZ3, 3BW2, 3A3C.




EDIT: you might have more details on your experiment, that would be useful here, for eg. can you draw an approximate distribution of the x-ray emission as compared to the tube's perimeter?

Re: Russian 2X2 valve rectifier X-ray emission report
Proud Mary, Mon Dec 06 2010, 02:32PM

This Russian 2C2S is the 'equivalent' of 2X2A - which does not mean it is identical. It means that the pin outs are the same, and the principal parameters are similar, so the rectifier can be expected to perform well in circuits designed for 2X2A. The state-owned manufacturer may or may not have used the same alloys in the electrode assemblies, since 'equivalence' is an empirical concept based on actual working performance, and not on metallurgy and manufacturing processes.

An X-ray source emits two types of radiation, as we know - continuous radiation, the so-called bremsstrahlung or 'braking radiation,' and the characteristic spectra of the chemical elements being excited by the electron beam. It is here that we may discover big differences between
2C2S and 2X2A, and perhaps even between batches of the same valve, perhaps reflecting changing costs in the metal market

I have not personally examined the American 2X2A, so what I say here is my opinion based around the Russian 2C2S.






The sharp and jagged edges seen in these pictures all become significant sources of field emission at high voltage. (This is just a valve
I've taken at random out of a box in my stack)





While the anode has been carefully shaped to avoid sharp edges, the ends of the terminals spot welded to the top are sharp wedges
presumably made by hand-held wire cutters.





Now here below is what I call a real girl power rectifier - the legendary Russian V1-0,15/55 * - which is what it says it is - a 55kV 150mA rectifier, which emits abundant radiation whether you like it or not.

Tired of those fussy little HV silicon diodes that go phut at the smallest sign of a flashover? The V1-0.15/55 is the answer to your prayers! Worried your X-ray tube isn't emitting all you hoped it would? Use the V1-0.15/55 and let it add its own soothing rays to the radiation emitted by your tube.





Yes, girls, it really is true! Tests prove that nine out of ten women who expressed a preference for Russian high voltage rectifiers chose V1-0,15/55!






Warning: Not suitable for pets or children under six.





Warning: May cause permanent chromosomal change



* I have written this in Roman script. In Cyrillic it looks like B1-0,15/55

Re: Russian 2X2 valve rectifier X-ray emission report
radhoo, Mon Dec 06 2010, 08:14PM

Actually the seller was from Lithuania, so looking closer I can see it is the 2C2S . They should arrive in a couple of days.

Proud Mary, What's with all the pink colors in your post?

Indeed it crossed my mind to try a multiplier out of DY86's. Would be an interesting piece.

Thanks!

Re: Russian 2X2 valve rectifier X-ray emission report
Proud Mary, Mon Dec 06 2010, 08:45PM


I think perhaps we have a different sense of humour!

Re: Russian 2X2 valve rectifier X-ray emission report
radhoo, Tue Dec 07 2010, 02:13PM

nice to see you're in a good mood, it is almost contagious.

so what do you think, will this diy rectifier-tube approach work with an intensifier screen?

Re: Russian 2X2 valve rectifier X-ray emission report
Proud Mary, Tue Dec 07 2010, 03:05PM


First, do not apply heater current, as this will cause the voltage drop across the rectifier to fall to 200V or so. You must use the valve in field emission - cold cathode - mode.

If you put 30kV and more across the 2C2S, you'll have enough X-rays to make a Gd2O2S screen fluoresce, and form an image.

Now, if you reverse the normal polarity of the valve, connecting EHT+ to the cathode on pin 4, and the anode top cap to Earth, you will get a sharper image by reducing the target size. This will also increase the impedance of the valve, keeping the voltage drop across it
to a higher level than the conventional polarity and so help to produce plentiful field emission.

If you hold the valve with the top cap uppermost, then most - but not all - of the radiation will come from the open end of the anode 'bell' -
from almost at right angles to the vertical axis of the valve, and to about 45° down from this all round. The emission will occur
unevenly round 360° with the valve at the centre of the circle.

If you had 50kV/50µA across 2C2S, the dose rate distributed around a circle of radius 200mm would be somewhere between 2 and 4 Sv/hr - a non-trivial quantity.

To reduce the risk of flashover, and glass 'puncture' failure, I'd suggest putting the valve in a bath of vegetable oil - sunflower seed oil, and so on. You should not expect the tube to last long, even with this precaution, but it will last longer!

Re: Russian 2X2 valve rectifier X-ray emission report
radhoo, Tue Dec 07 2010, 03:17PM

I couldn't dare to waste your time, but just to make sure I got it right, would you draw a simple sketch of the tube's optimal position? You know what it is said about pictures as compared to words. In geometry this comparison goes even further.

Thanks!

Re: Russian 2X2 valve rectifier X-ray emission report
Proud Mary, Tue Dec 07 2010, 03:43PM






I think the field emission is coming from the sharp edge of the anode 'bell' or 'thimble' and impacting on the rods going up to the heater and cathode.

Re: Russian 2X2 valve rectifier X-ray emission report
radhoo, Tue Dec 07 2010, 09:10PM

I was just imagining some x-ray sensitive (photosensitive maybe) non-conductive foam, put in a recipient around the tube, powering the tube, then carefully dismantling the foam to see the beams pattern.

Besides this, is there a realistic approach that I could use?

What about shielding the tube in lead, except a tiny hole, checking the output, then moving the tube inside the shield, checking again and so on, for optimal output?

What about the measurements? I've got the following:




All geigers.

I also have the CDV 717 (ionisation chamber: bottom ) however there's that joke that the CDV 717 measures how dead you already are.

Then there's the CI-12B and a custom made circuit:
Unfortunately the CI-14B was over-volted before I got it so it was useless.

Any suggestions on how to get an idea of the actual X-rays level? The Radex 1706 is very sensitive, it goes screaming near an over-volted DY86 , but I'm not sure how reliable it is.

I know it is said that geigers are not good for X-rays, but why?

Re: Russian 2X2 valve rectifier X-ray emission report
Wolfram, Tue Dec 07 2010, 10:28PM

You could wrap some x-ray cassette screen around the tube, and photograph it from different angles in a dark room.

Here is a link to a video with the best x-rays I've seen taken with a normal vacuum tube and a fluorescent screen. I would say it's absolutely worth a try. If you are serious about this hobby, much better results can be had with a proper x-ray tube though, example here . Dental ones are practical in size, so I would suggest buying one if you find a good deal.


Anders M.

Re: Russian 2X2 valve rectifier X-ray emission report
radhoo, Wed Dec 08 2010, 12:01AM

Thanks, Anders.

How about the flash x-ray tubes manufactured by Svetlana? Proud Mary posted a few pics in the Projects section for his X-ray spectrometer.

Re: Russian 2X2 valve rectifier X-ray emission report
Wolfram, Wed Dec 08 2010, 12:24AM

Hello.

The tubes Mary posted in her spectrometer thread are not flash x-ray tubes, they are regular x-ray tubes with beryllium windows, made for x-ray fluorescence applications and such. Unfortunately these are not really that well suited for general radiography, as they are made for relatively low voltages and currents. They would work fine for radiography of flowers, insects and things like that, which can be very interesting.

I don't see any dental x-ray tubes on eBay right now, but there are ones for sale there regularly.


Anders M.

Re: Russian 2X2 valve rectifier X-ray emission report
Proud Mary, Wed Dec 08 2010, 12:44AM


These are not flash X-ray tubes, Radhu, as Anders has kindly pointed out. Flash X-rays tubes work by a special case of vacuum breakdown with heavy conduction and very fast rise time in the nanosecond regime.

To follow Ander's point, Svetlana do have a very stylish little X-ray tube in the dental industry standard ~70kV 7mA in this season's catalogue:











My beautiful analytical X-ray tubes work at very low power levels compared with a dental tube. The reason I am able to power them with an ignition transformer and a two stage full-wave Cockcroft and Walton multiplier at 50Hz is because these tubes have maximum anode currents of 600µA. Notice that the two types I have selected for this series of experiments do not even have water cooling, yet they can run happily for 48 or 72 hours continuously, which can be necessary in the primitive form of X-ray crystallography possible with my simple equipment.

My main interest is the X-ray world below 10keV. At the moment I can both generate and detect X-rays of 4keV, but hope to get down to 2keV in the next year. This is where much of new X-ray research is taking place, so I shall be in good company!

I have answered all of your questions relating to the highly non-linear energy response curves of GM tubes so many times before that if you search Google Images for "GM tube energy response" you will be directed to some of my previous answers here on 4HV.org.

As for your GM pancake detector, it may have failed as you suggest, but the same symptoms are produced by combinations of HT+ too high, anode resistor too low, and too much capacitance in the anode circuit.

Remember it is the job of the anode resistor to pull down the voltage across the tube to below the conduction potential after each Townsend avalanche, so if the resistance is too low, the tube will not quench, and continuous conduction may occur.

You will see that excess capacitance in the anode circuit will also tend to prolong the current pulse during conduction events while the capacitor discharges through the tube- which is why it is always best practice to extract the signal from the cathode end, although this is rarely done in hobbyist designs. Excess capacitance at the anode is the biggest single cause of erratic performance, pulse pile-up, increased dead time, and reduced tube life in GM tubes.*

I would suggest increasing the anode resistor to 20M, and seeing if this cures the fault, though you may have to increase the supply voltage to make this work.

There are - or more correctly were - specialist X-ray detecting GM tubes containing Xe, chosen for its high atomic number compared with the other noble gases. These tubes were operated at a much higher pressure/counting gas density than is usual in GM tubes, to increase the chance of collisions.

Today X-rays are measured by ionisation chambers, proportional gas tubes, GEM and micro-channel detector arrays, by scintillation counters, and solid state detectors, of which there is an ever growing number of varieties - RADFETs, PIN photodiodes, germanium detectors, diamond detectors, and so on.

* Centronics GM Tube Handbook.

Re: Russian 2X2 valve rectifier X-ray emission report
radhoo, Wed Dec 08 2010, 11:46AM

Proud Mary, sorry for the confusion, and congrats on the high level of knowledge you've achieved in this very technical field.

Time ago, I've seen some flash tubes on a webpage or (not sure) on Ebay (you might know the seller, denys2472 ), and the shape was extremely similar to those you've pictured. So in a superficial, quick assumption, I concluded they were the same type.
Now doing a quick search, the differences are obvious:

Anyway, changing topic, I assume my SI14-B is dead. The electrodes seem corroded in a HV style . The seller said he tests all his tubes, but I don't know if this is good or bad, I assumed he just put too much voltage/current in it.
The tube is initially stable, at lets say 400V . Then when the first particles enter the tube, they trigger a continuous conduction. I need to follow your advice and see the results. Some more questions:
- what about the SI-12B? ( I hate the diameter difference, but this is all I have)
- assuming the SI-14B is not dead, is it usable for detecting/dosing x-rays? I've look over the energy response graphic, that you've posted before. I will need to read/understand more on the topic before I can comment.

I am aware of the scintillation counters, you've seen mine :(
Regarding ionization chambers, I tried building one, but at that time I didn't have a suitable resistor to convert the very tiny current to a measurable voltage, probably I should give it another try.
Photodiodes unless they are manufactured for this purpose, I don't think regular ones would be efficient.
As for Radfets they might be abundantly available the next few years, but currently they are not really an option for a hobbyist.

I'd like to know more about your detection mechanism , especially one that can go as low as 4keV! I assume you've built a ionization chamber?
I hope my scintillation probe is not dead. Despite the small crystal surface, would be a very good tool. I could also try to replace the crystal with a piece of Intensifying screen material from a X-ray cassette.

Re: Russian 2X2 valve rectifier X-ray emission report
Proud Mary, Wed Dec 08 2010, 01:56PM

I've bought from Denys perhaps a dozen times in the last few years, but I've never known him to have any flash X-ray tubes for sale.

Les Wright - "Plazmatron" in this forum - is the only person I know of who has done any experiments with flash X-ray tubes. He really loves them in the way that you might like brânză de burduf with a glass of tuică to wash it down.

Perhaps - but Soviet soldering can often look like that.

You should remember that the sensitivity of gas detectors like GM tubes is strongly related to the counting gas volume. A big tube is more sensitive than a small tube because there are more atoms of gas for particles to interact with. As there are more interactions, we have bigger samples, and so greater accuracy in any one counting period.

I've just taken this picture of my G26 GM tube to give you some idea of the size of a dedicated X-ray GM tube. (This tube is a relic of the Heroic Age of Atmospheric Atomic Tests, a technical fossil of those heady days when the World Superpowers shared out abundant radio-iodine and Sr-90 to the children of the world, so none would be left behind by technical progress.)








Don't worry if you've damaged the PMT. It's much easier to get a good cheap Russian PMT, than it is to get a decent piece of NaI(Tl)


Don't. You need equipment you do not have to calibrate and make sense of them. You cannot use scientific toy ionisation chambers when you are working with real X-rays.


You are not right to say that common PIN photodiodes are unsuitable for X-ray detection.

These three patents - issued to the UK National Radiological Protection Board - use the common PIN photodiode BPX65 as a radiation detector.





The quantum efficiency of PIN photodiodes increases with decreasing X-ray energy, so that at 1keV efficiency is almost 100%.

BPX65 has a plastic lens which must be removed for detection below about 10keV. I have bought BPX65 on ebay for a few Euros, and similar but unbranded PIN photodiodes for much less. Making the charge amplifier to use with PIN photodiodes in photon counting mode is not difficult, but requires a very careful and disciplined approach if it is to work well because of the microscopic currents involved. Here is an application note from Maxim giving a complete circuit for a PIN photodiode gamma detector.


With X-rays you can use the PIN photodiode in continuous mode (easy!) because you are not trying to detect individual tiny charges.


Again, not true. A number of cheap p-MOS transistors will give good results, which is how it was discovered in the first place.

I have just designed a very simple but effective and reliable sensor for X-ray dosimetry, and am experimenting with it at the moment. I will give out details in a few days when I have fully tested it, and will in any case be sending a few out to friends in the forum as a small Christmas gift.

Re: Russian 2X2 valve rectifier X-ray emission report
radhoo, Wed Dec 08 2010, 02:31PM

Off-topic, you seem to know a lot about RO ("Branza" and the other things you said in older posts). Most of us use US layout keyboards, so we usually skip the diacritics. Should I write it like you did , I would need to find the unicode/utf-8 character code. We also have "urdă", but we buy "Ricotta", because like all our other values, they fall without a strong spirit.

I also have this big tube (I.F.A. G64W ):



But didn't have the time to run tests on it, and a quick search revealed nothing.
Your arguments stand, I'd add that the bigger the tube, the more space is checked for radiation, meaning that I would prefer to use a big detector next to my source, then a small one that maybe skips some readings because of the field's distribution/repartition.

For the same reason I was delighted to see the big mica windows of the SI-14B. You've revived hope for this one, and there are chances it would still work. In some rare cases the avalanche discharge stopped, so a bigger resistor might actually transform this into a very stable detector.

It was a nice surprise to see the material on Maxim's site. Indeed this is what I would also call "innovation" (delivered). The attribute exotic might also fit in well :) . So all in one I will consider this approach, I must admit that I fell safer with so experienced people around, and seeing other experiments.

The BPX65 is currently unavailable on ebay, however this little photodiode reminds me of one that I took out of a floppy driver - disk present checker. I understand that the goal is to have the semiconductor crystal as exposed as possible, so removing any extra-plastic would help?

The last part of your reply, reminds me how I cut the metal case of germanium transistor, cleaned the white substance to get a photodiode. I'm sure that to some degree, the photoelectric effect would work with x-rays as well.
On the other hand a 2n3055 transistor has a very big Si crystal, totally exposed if you remove the metal cap (very easy). Would that work?
What about an array of such tiny semiconductor detectors, arranged like the photo-cells in a fly's eye?

What about using CCDs directly?

Re: Russian 2X2 valve rectifier X-ray emission report
Proud Mary, Wed Dec 08 2010, 05:04PM






As you can see, these tubes have been made to a very low standard, probably to meet the production quota of a 5 Year Plan. I call them the Little Blue Horror because the glass is so thin and fragile that you can break them with your breath. But the thin glass makes them a very good detector despite the poor engineering of the base and its pins. They were all made in 1960 - 50 years ago.





The ageing paper wrapped around the tube is its data sheet, each one filled out by hand after measuring the characteristics of one particular tube, a time consuming labour that you no longer see today except for very expensive hand-built parts like some X-ray tubes, big hydrogen thyratrons, and so on.






A very fine tube you have there, Radhu. I would guess it is a high voltage type - somewhere between 950V and 1150V - but that is only an educated guess. It will not be difficult to make a graph of its curve, but you must have a variable voltage supply 300V - 1200V.


Yes, that is possible. Pancake GM devices are used mostly in close up contamination detectors - used for examining people and surfaces for nuclear bomb fall out ash in this case. They will detect some X-rays, but are not designed to do so. The distance through the counting gas between the front window and the back is very short, and there is not much metal there for X-rays to knock electrons out of - the main source of GM events for X and Gamma rays.


I have other circuits for use with PIN photodiodes using cheap electrometer FETs in the critical first stage.


Very soft X-rays can only travel a short distance through the air, so even very thin plastic will block rays below about 2 or 3keV. Experiments must have both the X-ray source and the detector in the same vacuum space.



I'm sure you know that big old transistors are often packed with beryllium oxide, a very toxic carcinogen. Facts/SF301.pdf



There are a thousand and one experiments you can do to try and create new detectors, or improve old ones. But I would encourage you to have at least two completely reliable systems for detecting and measuring X-rays before you go much further.

CCDs are becoming more and more important in X-ray detection and imaging. For one example only:




That's enough for now. You have me all worn out with all these questions!

Good Stuff Added Later

I have found some references to your G64W GM tube!

Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment
Volume 339, Issues 1-2, 22 January 1994, Pages 329-333.

Measurements of the level of soil contamination using helicopters

D. M. Farcaiu, Maria Sahagia and Stefania Sahagia
Institute for Physics and Nuclear Engineering, P.O. Box MG-6, Bucharest, Romania

Here we learn that a "system type ASGM 25 which contained a battery of 72 GeigerMiiller counters type G64W (Romanian, organic gas filling, 32 mm diameter and 360 mm length)" has been installed in a helicopter to look for 'lost' (really!) Co-60 and I-131 in the Romanian countryside and forests.

Then in this paper:
Comparative Technology Transfer and Society, Volume 7, Number 1, April 2009, pp. 66-110 (Article)
Analysis of Soviet Technology Transfer in the Development of China's Nuclear Weapons
Liu Yanqiong
Liu Jifeng

we learn a bit more about the "ASGM 25" special equipment:

"Uranium prospecting: The Soviet Union hoped to obtain uranium from
China, while China wanted to acquire the Soviet’s advanced technology and
equipment. Under Agreements 55.01 and 56.12, the Soviet Union agreed to
provide these for uranium exploration. Regarding prospecting equipment and
apparatus, the Soviets provided aircraft, comprehensive aerial-surveying instruments,
radiation devices, and logging measurements. Prior to Agreement
54.01, when Soviet expert Lazutekin assisted China in uranium exploration,
Geiger counters were used—the first radiation detector made in China, which
had been assembled by the Institute of Modern Physics (Liang, 2007, p. 25).
Under Agreement 55.01, the Soviet Union did provide some equipment and
technology, including an AN-2 aircraft for aerial surveying, a set of ASGM-25
aerial-surveying instruments, and a complete crew for aerial surveying. Prospecting
crew 309 then organized an air force survey team (Wen, 2005)."

The first statement that G64W has an 'organic gas filling' tells us that it is a high voltage GM tube. Organic quench gas - very often ethanol vapour -
is an older technology than halogen quenching, and is typically used with a so-called Penning gas mixture in high voltage tubes. The plateau length in organic quench tubes is usually 200-300V, so it would be safe to start the tube at 1050V - 1100V with a 20M anode resistor, and it will probably work straight away (if it it still in working order, of course!)

You will notice that G64W is described as having a length of 30cm - this its effective length - the length of the sensitive detecting part - rather than the mechanical length, including terminals etc, which is obviously longer.

Re: Russian 2X2 valve rectifier X-ray emission report
radhoo, Wed Dec 08 2010, 06:43PM

Indeed :) Your time and valuable explanations are much appreciated!

Re: Russian 2X2 valve rectifier X-ray emission report
Proud Mary, Wed Dec 08 2010, 06:51PM


Radhu, I added a bit about your big GM tube to my last post above while you were posting your reply, so you may not have seen it.

You'll understand that by using 72 GM tubes in 'Soviet apparatus ASGM 25' they have multiplied the detector volume of counting gas by 72, and so increased the system sensitivity to a very high degree.

Why can't I have Soviet apparatus ASGM 25?

Re: Russian 2X2 valve rectifier X-ray emission report
radhoo, Wed Dec 08 2010, 08:44PM

I've got some ideas on how to optimally use my Geiger tubes. So this is what I came up with:
1. I will use an inverter driven by 2 AA batteries. The inverter will use a High Freq ferrite small transformer (found in many supplies), with an output close to 1200V and a very small current capability.
2. This supply might use or not a small multiplier to achieve 1200V, but the output will be regulated, either by driving the excess voltage to ground, over Zener diodes, or using the Zeners to open a transistor that would stop the oscillations (optimal energy usage). I did some tests for both and all is good. Using some jumpers connected next to the Z-diodes, I will be able to precisely select the output voltage (for variosu tubes).
3. The counter will use a high ohmic resistor connected to the tube's anode , to collect the signal which will be driven to the ADC entry of an ATmega8 microcontroller.
4. The microcontroller will count the pulses, do various calculations.
5. Optionally the microcontroller could use an output pin to control the HV supply for X-rays via a relay or some other mechanism.
6. The microcontroller will have a Bluetooth TTL Chip attached, as shown here:

so I could remotely read data and/or control the HV supply for the x-rays.
7. On a second thought I might use PWM from the ATMega8 directly to drive the little ferrite transformer for the tube's supply.

Is there anything else I need to consider for this detector?

Re: Russian 2X2 valve rectifier X-ray emission report
radhoo, Wed Dec 08 2010, 09:30PM

What is really happening here: ?

Re: Russian 2X2 valve rectifier X-ray emission report
Proud Mary, Wed Dec 08 2010, 11:24PM


Who can say? X-ray emission often - but not always - causes glass to glow yellow-green or blue, depending on the energy of the rays, and the chemical composition of the glass.

Anyway, the time has come for you to stop guessing what may be happening in your experiments, and finding out what is going on by using appropriate radiation tools. If that tube in your video was emitting X-rays, you may have received more than one year's normal background radiation exposure - say 2.5mSv - so you can fool around no more - not if you want me to help you at any rate.

You should read carefully the Centronics Geiger Müller Tubes Theory handbook, as this will help enormously in developing ideas about what to do with your G64W. You can download it as .pdf here:

Re: Russian 2X2 valve rectifier X-ray emission report
radhoo, Fri Dec 10 2010, 05:47PM

I've just started reading it, thanks.

The previous experiments where done with the camera on tripod+timer, and I was like 8 meters away, in another room, with some concrete walls in between. I had no measurement instruments back then, not even a GM Dosimeter, but the distance should have kept me on the safe side.

Re: Russian 2X2 valve rectifier X-ray emission report
radhoo, Sat Jan 15 2011, 11:26PM

some interesting results using 2X2: