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Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
Steve McConner wrote ...
Interesting, thanks!
I had a quick look on Ebay, and found a really beat-up looking one, missing the probe head, for 99p.
I also found this:
which might be useful for uranium prospecting. It's the Trainer No. 1, an extra-sensitive counter for use with weakly radioactive practice sources. The readout is in micro-roentgens per hour.
I had a Trainer No.1 some years ago, and modified it with a 555 driven switching transistor and step-up transformer to supply the HT from four 'D' cells. It does have a very sensitive glass tube about 200mm long, from memory, but for all else it is even worse than those yellow bricks with a handle on them. It could detect a small lump of pitchblende at about one metre.
If you can find a working example for less than twenty quid or so, it's worth buying just for the sake of the GM tube, as good glass tubes are often hard to find. The rest is best put into a recycling bin.
Not to be confused with the identical looking but very insensitive unit for which the Trainer No. 1 provided training.
Registered Member #2261
Joined: Mon Aug 03 2009, 01:19AM
Location: London, UK
Posts: 581
Proud Mary wrote ...
There's a super circuit using a 4049 Hex Inverting Buffer/Converter in the front end of a particle detector on the cosmicrays.org site here:
As you see, it is a coincidence detector circuit, but you can erase one stream of the circuit, and the circuitry downstream of the 555 for your purpose. The use of the 555 to make a variable output pulse width offers useful flexibility for interfacing with other circuits.
You'll also find other handy and inventive GM circuits on cosmicrays.org....
Ah! Yes, I like that circuit by Joseph DiVerdi! The 4049 has high impedance CMOS inputs which also allow the input signal to exceed the 4049 +ive supply voltage, which might be useful, but might cause ringing or something (scope ). 4049 data sheet here:
It uses pairs of gates to generate 1uS low going pulses which in turn trigger the 555 timers to produce well defined pulses for each tube firing. I’m not clear why it uses these two different pulse shaping circuits in series.
Registered Member #2261
Joined: Mon Aug 03 2009, 01:19AM
Location: London, UK
Posts: 581
Proud Mary wrote ...
I had a Trainer No.1 some years ago, and modified it with a 555 driven switching transistor and step-up transformer to supply the HT from four 'D' cells. It does have a very sensitive glass tube about 200mm long, from memory, but for all else it is even worse than those yellow bricks with a handle on them. It could detect a small lump of pitchblende at about one metre.
If you can find a working example for less than twenty quid or so, it's worth buying just for the sake of the GM tube, as good glass tubes are often hard to find. The rest is best put into a recycling bin.
Not to be confused with the identical looking but very insensitive unit for which the Trainer No. 1 provided training.
How do you think that tube would compare to the Russian one I got?
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
IntraWinding wrote ...
Proud Mary wrote ...
I had a Trainer No.1 some years ago, and modified it with a 555 driven switching transistor and step-up transformer to supply the HT from four 'D' cells. It does have a very sensitive glass tube about 200mm long, from memory, but for all else it is even worse than those yellow bricks with a handle on them. It could detect a small lump of pitchblende at about one metre.
If you can find a working example for less than twenty quid or so, it's worth buying just for the sake of the GM tube, as good glass tubes are often hard to find. The rest is best put into a recycling bin.
Not to be confused with the identical looking but very insensitive unit for which the Trainer No. 1 provided training.
How do you think that tube would compare to the Russian one I got?
I don't know enough about either to have formed an opinion. Generally, metal skinned tubes are more robust, though there are exceptions even to this - the Victoreen 1B85 beta-gamma tube was famous for its ability to collapse under the pressure of its own vacuum with only light finger pressure.
Registered Member #2123
Joined: Sat May 16 2009, 03:10AM
Location: Bend, Oregon
Posts: 312
The beta-gamma GM tube Proud Mary mentions may be the mica-windowed 5979.
In addition to the one in the probe of my radiacmeter, I have the two spares (see photo). These need ~700 volts to operate.
One has the mica window painted black, the other (with the more elaborate window cap in the photo) has a clear window, and a glow can be seen in it when at voltage and presented with a 7uCi gamma source. I didn't know it could sense UV.
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
MinorityCarrier wrote ...
The beta-gamma GM tube Proud Mary mentions may be the mica-windowed 5979.
In addition to the one in the probe of my radiacmeter, I have the two spares (see photo). These need ~700 volts to operate.
One has the mica window painted black, the other (with the more elaborate window cap in the photo) has a clear window, and a glow can be seen in it when at voltage and presented with a 7uCi gamma source. I didn't know it could sense UV.
What you call black paint on the end mica window of your Electronic Products Co. 5979 is in fact aquadag - conductive colloidal graphite paint.*
The tube in the Meter Contamination No. 1 ancillary parts inventory was a glass wall tube type - perhaps one of the B12 series - and as government contract manufacture would certainly have been Made in England in the early 1950s.
You almost never see this probe included with second hand sales of the instrument, probably because of the vulnerability of the glass tube inside its aluminium housing, compared with the armoured rubber GM tubes also supplied with the outfit.
The single prong plug connector often seen in American and Russian GM tube design has never, to my knowledge, been used in British manufacture, which has favoured the B2, (i.e. British 2 pin as still used in many of the Centronics ZP series, and hard to get if you don't want to pay the eye-watering new price from Centronics) the B4, used in the now obsolete G series, and the International Octal, as still used in the Centronics B series glass wall beta-gamma tubes.
Now as to the detection of UV photons originating outwith the tube, don't forget that the Townsend avalanche consists of Primary and Secondary avalanche components. In the primary avalanche, your gas molecules (Ar, Ne, etc) are not only ionized, but excited. When these de-excite, they emit a UV photon. These UV photons hit on the gas molecules causing further ionization, which sets off secondary avalanches until the entire length of the anode is involved. So you'll see that as UV photons are an essential part of the GM process, those that get into the tube from outside will also trigger avalanches and so cause spurious counts.
*Atomic Energy Commission Radiation Instrument Catalog, July 1st 1950, entry BG-1A29A.
Registered Member #2261
Joined: Mon Aug 03 2009, 01:19AM
Location: London, UK
Posts: 581
Here's an interesting old article from 'Popular Science', May 1955. It appears a 'Uranium Rush' was on in the US! It has a 6 tube option.
Super Geiger Counter By Howard G. McEntee
I'm surprised to see the Anode resistors bypassed with capacitors. I've been thinking about ways to improve Geiger tube recovery time and I wonder if that's what they're intended for?
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
IntraWinding wrote ...
Here's an interesting old article from 'Popular Science', May 1955. There appears to have been a 'Uranium Rush' was on in the US! It has a 6 tube option.
Super Geiger Counter By Howard G. McEntee
I'm surprised to see the Anode resistors bypassed with capacitors. I've been thinking about ways to improve Geiger tube recovery time and I wonder if that's what they're intended for?
Those caps are yer actual compensation* for stray capacitance when you consider the tube as a generator in the middle of a potential divider. Have a dekko in the Centronics GM tube bible here:
As it happens, I've got a few of those 5886 electrometer pentodes somewhere, but I wouldn't waste them on a GM circuit which could be better done using el cheapo FETs like 2N3819, and work all the better for it.
It seems a pity to use so many GM tubes in parallel like that, when a lot more could be done with them - such as coincidence and anti-coincidence counting - but the use of thermionic valves imposed great austerity of design on equipment intended to be portable. .
As for the early Cold War uranium bonanza in the USA: "As the only legal purchaser of the ore, the Atomic Energy Commission established minimum prices, guaranteed the rates for ten years, and added a $10,000 bonus for each separate discovery and production of high-grade uranium from new deposits."
Quoted from here:
I believe a similar government initiative promoted uranium prospecting in the Commonwealth of Australia during the "A-Bomb" years.
* Not to be confused with a tube's energy response compensation using metal foils (often tin) as filters wrapped round all, or part of, the tube
Added later: If you find that your tube is a 390V type, don't bother to make an HT PSU for the rig, as I have enough miniature 9VDC-500VDC modules to spare you one. They're about the size of two sugar cubes and came from a Harwell junk clearance auction. I always think that if ex-Harwell kit was thought good enough to have helped blow up Maralinga, Montebello and Christmas Islands, and parts of the Nevada desert, they must be good enough for me!
Registered Member #2261
Joined: Mon Aug 03 2009, 01:19AM
Location: London, UK
Posts: 581
Proud Mary wrote ...
Those caps are yer actual compensation* for stray capacitance when you consider the tube as a generator in the middle of a potential divider. Have a dekko in the Centronics GM tube bible here:
I picked up your mention of that guide in an earlier post and have read it. Thanks - the best I've seen (shame it's a scan of a poor quality printout though - I'm almost motivated to recreate it, but that's a lot of work and perhaps someone has a better copy already?).
The way I understood the compensation thing is by analogy to a x10 scope probe where you have to have the capacitive division ratio equal to the resistive to get faithful wave shape out. With the usual Anode/Cathode resistor ratio of 45:1, the capacitance parallel to the Cathode resistor should be 45 x the sum of the tube & Anode resistor capacitances. Normally you aim to keep the later pair as low as possible, but in the Popular Science circuit they've added capacitance on purpose in parallel to the Anode resistor!
Presumably then this dire act is a consequence of a huge Cathode resistor capacitance then? Is that something you get with valves?
Proud Mary wrote ...
Added later: If you find that your tube is a 390V type, don't bother to make an HT PSU for the rig, as I have enough miniature 9VDC-500VDC modules to spare you one. They're about the size of two sugar cubes and came from a Harwell junk clearance auction. I always think that if ex-Harwell kit was thought good enough to have helped blow up Maralinga, Montebello and Christmas Islands, and parts of the Nevada desert, they must be good enough for me!
Wow! Thanks. That will save a lot of tinkering! I'm pretty much certain it will turn out to be low voltage and most likely 390V. May I PM you if so?
Can I ask how you manage to get Harwell stuff (without revealing your 'trade secrets')? I use eBay all the time, but that's all I know for used kit.
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
IntraWinding wrote ...
Wow! Thanks. That will save a lot of tinkering! I'm pretty much certain it will turn out to be low voltage and most likely 390V. May I PM you if so?
No probs!
As for the Centronics GM theory book, I doubt that they will reprint it now. The days of the GM counter are fading fast, as new technology replaces the vulnerable glass to metal seals, the hunch-back energy response curve, significant dead time, and the problem of saturation at high count rates.
Other ionized gas detectors are still mainstream, but have moved away from the coaxial cylinder topology, towards devices like GEMS and Thick GEMS which I mean to try out using padboard and Veroboard. Read a few of the GEMS and Thick GEMS papers online and tell me if you thick Veroboard might just work.
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Radioactive Mineral Sample Prospecting Equipment - Advice Sought
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Wow! Thanks. That will save a lot of tinkering! I'm pretty much certain it will turn out to be low voltage and most likely 390V. May I PM you if so?