DIY gas filled proportional tubes

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ChristofferBraestrup
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DIY gas filled proportional tubes

Post by ChristofferBraestrup » Mon Jan 18, 2021 11:26 pm

"...How hard can it be?"

I'm messing around with making gas filled proportional conuter tubes, since I saw a figure in an unrelated paper that answered my biggest issue - how to get a thin anode wire perfectly taut and straight down the axis of the tube.

The answer is an internal support structure pulling the wire taut by a spring, the wire crimped into stainless capillaries.

I've created something very similar with hypodermic needles and a ballpoint pen spring. This assembly is supposed to fit into a 15 mm dia copper tube.

The non springy end has the anode soldered to a little flat copper disc on the end of the plastic part of the needle. This will contact the centre of a hermetic bnc just by pressure, provided by a second larger spring pushing this entire assembly against the other end cap ( with gas fill tube).

The long springy needle is sliding freely in the hole, and the wire is just crimped with a dulled and rounded over side cutter. The two end plates are 13 mm dia acrylic and the two stiffeners are 1/16 stainless capillary - this may be replaced with acrylic strips in the future. The anode wire is the thinnest copper wire available to man: a single strand extracted from cheap hifi cables.

If this behaves just barely I will order some thin gauge tungsten wire for the task.

Geometry and materials choices are to be decided later.

I hope to have more updates on this soon!
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Richard Hull
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Re: DIY gas filled proportional tubes

Post by Richard Hull » Tue Jan 19, 2021 5:48 am

Great effort. Lots of forethought here. Flawless concentricity warranting smooth even fields within the detection area are a must. There can be no bulges or extra metal in the device as these are the norm in such endeavors. Thin wire to larger wire connections are always glass sleeved at their juncture to preserve the fine wire-to-smooth cathode shell field uniformity.
Such sleeves need not be sealed to the wire at all and can be left open to the fill gas. The ends of such sleeves define the sensitive volume. simple diagram below.

Note: I have made GM tubes before. I was planning on selling them. I have about 50 individual professionally made, functional GM tubes just laying around the two labs. Thus, making them for myself is a fool's errand, save for the experience gained in the doing and working. (it's all about the doing)

Unfortunately, trying to sell some of my fabulous mica windowed 5979 professional GM, (alpha, beta, gamma) tubes both here in the trading post and at numerous hamfests for 10 years had virtually no takers. LND gets $130 each plus $25 shipping. I offered them at $60 each at hamfests and $80 shipped in the US. I figured if I can't get that for the perfect 5979 replacement tube for the navy PDR-27J GM counter, all my hand labor to roll my own (beta, gamma) tubes for sale would be pure folly.

No one builds things anymore. The old hams of yesteryear are too lazy but capable to assemble their own counter around the hard to get mica windowed tube at a bargain price, while the young ones aren't real hams but two meter people, (a quarter of a useful notch above CB folks). The old technician class brass pounders that I knew and hung around when a kid are pretty much silent keys now.

Richard Hull
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Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
Retired now...Doing only what I want and not what I should...every day is a saturday.

ChristofferBraestrup
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Re: DIY gas filled proportional tubes

Post by ChristofferBraestrup » Wed Jan 20, 2021 12:02 am

Thanks for the heads up with the insulation around the non-wire parts of the anode!

How much the two metal struts impact the field remains to be seen.. According to William R. Leo's book on nuclear electronics the field at the tube wall is neglible, and electrons just drift lazily towards the anode, and charge multiplication happens only a few anode wire widths from the anode.

I've seen it done in a high temperature proportional counter (which was the inspiration for this project):

Image

source: https://www.researchgate.net/publicatio ... evaluation

Gas tightness was achieved by soldering the tube to a flanged BNC connector which hopefully is hermetic. The other end is fitted with a rubber serum septum cap that fit perfectly. this is bored out to allow for the very victorian stopcock. Alternatively and more modern, the detector can be charged with a un-holed septum, a hypodermic needle connected to a vacuum line, and one connected to a balloon of the desired fill gas. cycling between sticking in the vacuum needle and the balloon should flush the chamber pretty well. I guess that's a very chemist-y approach to gas handling!
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Richard Hull
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Re: DIY gas filled proportional tubes

Post by Richard Hull » Wed Jan 20, 2021 6:06 am

Yes, for an experimental situation, a fill stopcock is desired as one fiddles with successive gas mixtures until happy with the detection ability and plateau in the case of a GM tube. Proportional tubes do not usually have a complex mix of as many as three carefully metered in gases that are rather critical in the GM tube. In the case of the GM tube, the detector field design is rather critical as it impacts the quench and dead time to a marked degree in the case of a "fast counter". The collection time of the lumbering heavy ions to the shell is a slow trip long after the end of the collection of the electrons.

The early days of serious nuclear counting are interesting. There were four periods. 1. the early research used the photographic, scintillation counting, and electroscope methods 1898-1908.... Geiger made the first crude very slow counters which were not really electronic at all. 2. The second period where special sealed GM tubes with specific construction and gases were used and Mueller worked with Geiger to find organic quenching agents within the tubes that really increased their counting speed 1908-1925. 3. The electronic era came into being in the mid 1920's but only in special labs. All were hand built, including the GM tubes. This period lasted until WW-II. 4. The current era from the late 1930's and during WW-II until today when the tremendous need for reliable manufactured counting systems and special GM and proportional tubes made full use of electronics and modern infinite life tubes using halogen quench gases that made super fast counters a thing of common manufacture to all from Research facilities to schools an even the common home owner.

I really believe everyone here should save the following URL as it is a rich on-line museum of the history of radiation work in the last century. I give the directory page URL. For the purpose of this post, check out the early GM counter tube page and the proportional tube page to see just how sloppy many famous researcher used junk and sealing wax to make their research tubes as late as early WW-II. Remember there were no established manufacturers of GM tubes or counter systems until WW-II forced the issue. In the museum on GM tubes you will see that individual schools and scientists were still hand making their own tubes as late as 1950!! The cold war and post war research shoved the manufacture of these tubes into custom factory production in the millions of stable reliable GM and proportional tubes for use in many special counting situations. Thus, the 1950's might be regarded as the beginning of the first GM and proportional tube manufacture and sales.

https://www.orau.org/ptp/museumdirectory.htm

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
Retired now...Doing only what I want and not what I should...every day is a saturday.

ChristofferBraestrup
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Re: DIY gas filled proportional tubes

Post by ChristofferBraestrup » Wed Jan 20, 2021 11:29 pm

What a great resource!

DIY thin window GM tubes with cellophane coated in aquadag is definitely worth trying even today!

--I put some high voltage on my air proportional tube (until I find or make a fill gas), and at 1500-1700V I get plenty of tail pulses with differing heights. And this is by just connecting the tube through a bias box and cap directly to a standard oscilloscope through roulghly 20 cm coax.

With a CSP I'm sure the pulses will look much nicer.

At higher voltages, 2500-3kV, the tube was unstable, occasionally running smooth, then a pulse would set off a seconds long burst of very large ugly pulses - I believe this is the "continuous discharge" region where the tube basically ignites like a fluorescent tube. This makes sense as the tube is just filled with moist atmospheric air.

Either way a promising start. The tube is sensitive to microphonic effects, as the wire jiggles and field fluctuates.

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Re: DIY gas filled proportional tubes

Post by ChristofferBraestrup » Thu Jan 21, 2021 12:04 am

I learnt of a new proportional counter flavour from an 1960s educational chart I recently received.

The "proton recoil counter" - a proportional counter lined with a hydrogen rich material, from which fast neutrons would knock out protons to ionize the gas.

I've no idea if these caught on, or they stayed in the 1960s. Should be fairly easy to try out though!
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Richard Hull
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Re: DIY gas filled proportional tubes

Post by Richard Hull » Thu Jan 21, 2021 12:33 am

Yes, the ORAU museum site is choked full of goodies. I was poking around just a few minutes ago in the public consumer product part, I noted that a tape dispenser I have is shown to be radioactive!! They show a red one, mine is green. It is radioactive and the thorium signature shows on my gamma spectrometer in 2000 sec. It also tickles my Ludlum model 3 with 2" pancake detector. Those hot thorium gammas whistle right through the plastic!

https://www.orau.org/ptp/collection/con ... penser.htm

The earliest GM tubes were open to air! An open ended cylinder with a stiff wire was used first. Biasing and stability were beyond abysmal to terrible. Putting a mica window on it helped it go from rotten to merely very bad. pumping a bit of air out made it upgrade to just poor. These worked for sure, but required electroscopes to indicate a pulse rate just above background in the zero electronics era. Still, as terrible as it was, it beat sitting in the dark for 3 hour shifts counting pulses on scintillation screens. Geiger who worked with Rutherford for a period before WW-I had the terrible task of counting scintillations and was spelled in the effort by a "Miss Brooks", a doctoral candidate like Geiger. Is it any wonder that Geiger decided to monkey around with high field cylinders creating an environment that would count with micro pulses in air as alpha particles streaked into the cylinders blasting out 200,000 ion pairs in their path! Rutherford found Geiger a fine fellow once this odious duty was cast aside with those first terrible Geiger detectors. Rutherford constantly accused the human scintillation counters of falling asleep on duty, fouling "his data". (Read the history and you get cool facts like this)

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
Retired now...Doing only what I want and not what I should...every day is a saturday.

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Maciek Szymanski
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Re: DIY gas filled proportional tubes

Post by Maciek Szymanski » Thu Jan 21, 2021 10:35 am

There is a grat chapter on practical building GM and proportional tubes (1939 state of art) in "Procedures In Experimental Physics" by Roger Hayward

https://archive.org/details/in.ernet.dli.2015.212054/
“Begin at the beginning," the King said, very gravely, "and go on till you come to the end: then stop.” ― Lewis Carroll, Alice in Wonderland

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Richard Hull
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Re: DIY gas filled proportional tubes

Post by Richard Hull » Thu Jan 21, 2021 7:02 pm

I have 4 copies of that book that went through close to 15 separate printings from 1939 to the late 50's with a paperback reprint by Lindsay in the 1980's and 90's. Many of those 1939 procedures are still good for amateur use, today. The illustrations are flawless and from a bygone era.

The section on making your own GM counter is very good and the detailed and difficult passivation process of the copper GM tube shell is important to its success, if the tube is to be stable over a period of time. Passivation never left the GM tube shell game. This is due to the quench agents chemical reactivity with the shell. First it was organics and later the highly corrosive and chemically active halogen quench agent found in 100% of all modern tubes. Today passivation is not so bad as special, inert shell alloys resistant to specific halogens avoid this critical mission in GM manufacture.

Even some modern, not so great manufactured GM tubes are far better than anything that one might make privately. The Russian STS-5 tube is a great beta-gamma tube for about $20.00. Made by the countless millions after Chernobyl, they are a great surplus choice for a small, simple counter. Serious GM counters demand a 2" pancake tube, (alpha, beta, gamma), such as the LND 7311 for a bit over $100 each.

Accurate and stable proportional tubes can range from simple and easy to make all the way to a virtual impossibility at the amateur level.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
Retired now...Doing only what I want and not what I should...every day is a saturday.

ChristofferBraestrup
Posts: 110
Joined: Sat Apr 11, 2020 1:47 pm
Real name: Christoffer Braestrup

Re: DIY gas filled proportional tubes

Post by ChristofferBraestrup » Thu May 13, 2021 12:19 pm

I wonder if it would be worth puncturing one of the plentiful soviet GM tubes, to make an air proportional counter tube. I have a few large SI21G tubes (20cm x 20mm ish).
Walls feel thin enough to pierce with a sharp needle. cycling between rough vacuum and air a few times, then leaving under vacuum for a while would hopefully get all the quenching agent out.

Then one would end with an air filled tube with the right geometry. One could then make another hole in the other end and epoxy on some hose connections for gas-flow operation.

What do you think? Waste of a good tube?

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