Does anyone have any advice on the purchase of a geiger counter? New ones seem to cost $350 or more. There are refurbished ones from the 60's on
ebay for about half that price.
Does anyone have a geiger counter of some make that they are happy with? Or other advice?
Thanks.elementcollector1 - 17-10-2012 at 15:47
Ebay. Other 'used' sites. Incidentally, what do you need it for?Fossil - 17-10-2012 at 15:51
Try surplus stores, maybe even army surplus.12AX7 - 17-10-2012 at 16:16
Thanks, everyone. Element, I want it because I may be doing some thorium chemistry, or working with radon, and I'll need it to guard against
contamination. 12ax7, thanks for the link, they have interesting stuff there. There are old ones on ebay, but I'm not sure that they would be a good
investment. IrC - 18-10-2012 at 21:31
Look at the link above. This is what you DO NOT want to buy. So when looking around on eBay be sure you know the difference between a survey meter and
a Geiger counter. Virtually every survey meter listing has Geiger counter in the heading, a total lie. Assuming your survey meter works, any reading
on even the lowest scale implies you are not going to last long. You obviously want a true Geiger counter for looking at low level sources, bearing in
mind in a very high field the tube will saturate dropping your reading to zero. The Ostridge syndrome. When you walk into a deadly field your Geiger
counter will tell you there is nothing to worry about. Something I doubt you will ever encounter but it is good to understand the limitations of your
equipment. For low level testing I think the better instrument is a Scintillation counter, hard to find today and typically expensive. Sometimes you
find the great deal on eBay so it is worth searching. Do not buy the glass axial Russian tube at Goldmine or from eBay they suck. No sensitivity and
they fail often. The ultra mini metal tube which IIRC is $50 at Goldmine is only around $30 on eBay, an amazingly great tube. I built a mini detector
with one using a coin cell for power, and that counter never ceases to freak me out how sensitive it is, how reliable also.
The 6306 GM tube for $50 is your good old reliable. I just repaired an all chrome very rare 107C using the 6306 from Goldmine and four 6007 pencil
tubes I found on eBay. Works flawlessly now those NOS pencil (sub-miniature) tubes seem to be as good as new even a half century old. The ribbed
looking Russian tube is not so good either, not very sensitive compared to the 6306 and troublesome. The window for operating voltage is narrow and
flaky so If you decide to build one stick with the 6306. Do not apply pressure to the sides of the tube, do not solder to it especially on the end
(center wire) connection. Make some spring type connectors which do not require any force or twisting to connect to the tube.
If you take your time you can grab a decent Geiger counter under a hundred bucks so do not rush to buy one. The kits at Goldmine are not too bad
either and you learn something along the way.
You obviously want a true Geiger counter for looking at low level sources, bearing in mind in a very high field the tube will saturate dropping your
reading to zero.
This is a limitation in the way the signal is read out, though, right? Surely when the tube
saturates there's a much larger "quiescent" current (that is, non-pulsed) through the tube that could be sensed with comparator and used to light an
indicator lamp labelled something like "above upper range limit" or the like.IrC - 19-10-2012 at 17:00
While I am sure one could be designed to do that nothing typical on the market does. A diode detector could easily be designed to work like that. But
in any standard old GM device you are likely to find out there they all count pulses to indicate the flux whether averaged analog or digital counting.
When a Geiger tube is in a very high field of radiation it saturates making the reading fall to zero. No more pulses being produced means nothing to
measure as far as the circuitry can tell. Not sure if you are asking about what can be done or how do the typical units as designed operate. There was
one civil defense model on the market in the 60's which had ten GM tubes in parallel. One of my best hacker $5 finds at Greyhound Park swap meet in
Phoenix in the 80's. Gave me a pile of tubes to play with. It needed some subminature tubes which today online I could get easily but in 85 very hard
to locate using nothing but the Yellow pages. In any case even it would have done you in walking into a field greater than a hundred Rads or so by
dropping to zero. This is why they built ion chamber survey meters in the first place. Obviously it is very unlikely he will ever be in such a strong
field hopefully, I only mentioned it as I believe you should know the limitations of your equipment. Clearly they could have made calibrated shielding
for a GM tube for high field locations, but why would they when an ion chamber is just an empty can of air costing little to produce. They work great
in the hundred Rad or greater fields. Not like anyone is going to hang out long in such field intensities anyway.
Edit to add: you are right however, no idea why none of the old models worked with that thought in mind. After all they were in the height of cold war
paranoia as well as B movie radioactive monsters from space hysteria. Probably because they were only built for typical prospecting for low level
ores. They did know for high levels the ion chamber cost nothing to manufacture. AFAIK nobody used that principle, it sure seems a cool deadman
warning circuit could have been added to any of them. "Hey my tube just saturated were done for!".
Just don't know, cannot answer that one for you.
An afterthought: since they all used crappy blocking oscillator circuits maybe the HV just could not provide enough current to hold it saturated? I
know a latching circuit idea comes to mind. Possibly they were simply made for as little as possible with no though given to your question? Pretty
much every model I have played with had enough current to hold a GM tube in full saturation so I doubt even my afterthought has validity. The only
thought which comes to mind is hey we are smarter than they were in the 50's?
[Edited on 10-20-2012 by IrC]zenosx - 21-10-2012 at 19:21
I will say I own two from ebay, one is a rock solid airforce model from 0.1 to 500mR/hr. I can't remember the exact model, T-48 i think.
This was $350 and Very rare.
I also have a CDV-700 (the one with the hotdog probe on a wire), with beta window. It worked fine for about a month and died. I troubleshot it down
to a bad HV transformer, and the only replacement board I could find was being sold by a ripoff.
Anyway, point is, the old CDV counters are hit and miss, mine is in mint cond., but still doesn't work, others have Severe battery paste damage from
being stored 50 years with the batteries still in them.
If I were doing it over, I would spend the $150 on a modern counter.
Try UnitedNuclear.com, they have some O K low range counters good enough for contamination protection, and I think they will do alpha. They also have
other hard to find nuclear research materials like borated paraffin, and beryllium (if they have it in stock for neutron production).
I need an alpha probe myself but scintillation probes are SO expensive, and my counter is not modifiable. I use mine for uranium chemistry. So far I
have isolated yellowcake (Uranyl perodixe) and a few other compounds (oxides, nitrates, carbonates).
IF I get enough ore to work with again I will post my methods here. Good Luck.
