I have one.
Posted on 01/23/2008 3:47:38 PM PST by Aglooka
Any suggestions on good ones?
CAVEAT EMPTOR!
There are a LOT of things sold on ebay as "Geiger Counters" that are NOT "Geiger Counters"!
The most common is the "CDV-715" type, which is a "Survey Meter" -- it has an (internal) "Ion Chamber" (a big sealed metal can which may or may not be functional), instead of a "GM" (Geiger-Müller) tube, generally in a wand on the end of a cable.
So, why should you pay SO much more for a Geiger Counter, when a Survey Meter is so much cheaper? What's the difference, anyway? Oh, about several orders of magnitude.
A Geiger Counter will read SMALL amounts of radiation -- far less than the "kills you dead" level. Even a relatively cheap "CDV-700" type (note how similar the designation is to the "Survey Meter"?) will be sensitive enough to save you from Really Bad Stuff.
It will NOT read Alpha particles (not unless you buy a different probe), but, it WILL read fairly low levels of Beta and Gamma radiation.
How sensitive is a "cheap" Victoreen '700? Sensitive enough to give you a solid reading from a single (old style) lantern mantle (unburned of course), or some orange Fiestaware. Probably even some "salt substitute" (the stuff they use for that -- some type of potassium -- IS radioactive!)
It won't be able to detect the stuff that was used to murder that ex-Russian spy in England a few months ago, because that -- as deadly as it was -- was an Alpha emitter (unless I'm really misremembering things).
For more information, and to prevent buying something you'll regret having spent money on, I'd suggest subscribing to the "CDV700CLUB" mailing list:
CDV700CLUB website, with information on how to subscribe. Be sure to read a bunch of the archived posts (via the website) before jumping in with a bunch of "help me help me help me!" questions :)
That said, there IS a valid reason to buy a "Survey Meter" type device. With very high radiation levels (we're talking "aftermath of The Big One", or, serious "industrial accident" type levels), the GM tube in a GC will be swamped, and the meter will show NO radiation!
The "Survey Meters" are VERY useful for high radiation scenarios (the "is it safe to come out yet?" situation) -- which is why the government deployed massive numbers of them to the fallout shelters. (They had a variety of "standard kits" which included Survey Meters, Geiger Counters, Dosimeters (and chargers), and so forth.)
Your FIRST purchase, "IMO," should be a real Geiger Counter. A Survey Meter will NOT be of ANY use to you unless we truly enter the "Oh, SHIT!" existence. To put it another way, you will NOT be able to EVER see ANY reading on a Survey Meter (except for putting it into "Test" mode), unless you live a very, ahem, "interesting" life. For us normal folks, we are NEVER going to encounter the radiation levels that will even twitch the needle on a Survey Meter.
A Geiger Counter, however, WILL deflect pretty much all the time (!!!) That's because there is always "background radiation" -- and, by getting an idea of what normal background radiation looks like, you'll be able to quickly determine if you're measuring higher than normal levels.
The main thing is to NOT get swindled into buying an ion-chamber "Survey Meter", thinking it's a "Geiger Counter" -- even if the seller INSISTS that, yeah, it IS a Geiger Counter. If it's a "715" type (they had many different models, the 715 is probably the most common), it is NOT a Geiger Counter, no matter WHAT the seller promises you.
And, if it IS a Geiger Counter (i.e., a "700" type), make SURE that there is a "DOA" guarantee. There are a LOT of them that are defective due to age, use, abuse, etc. I've heard of a lot of them that were sold without A) the "check source" (a small radioactive "chip" on the side of the case, under a mylar label, which can be used to verify that the GC is operational -- hold the "wand" up to the "check source" and you should see the needle deflect -- the higher the sensitivity range you select, and the closer the wand, the more it will deflect (and, if you open the "beta shield" on the wand it will deflect a lot more). And, B) a lot of them are sold without the GM tube (in the wand) -- or, with a defective tube (or, defective cable, or defective circuit, etc.)
The GM tube consists of a VERY thin aluminum cylinder, with some connectors on one end, and a vacuum inside. HANDLE WITH CARE! If you give it "just a little squeeze" it WILL crumple up before your eyes!
So, make sure the seller gives you a "DOA" guarantee (and, make sure you have a way to TEST it when it arrives! I have read that ebay, in all their "wisdom" has cracked down on ALL sales of ALL "radioactive" materials, regardless of how harmless they are. As a result, a lot of (or all?) Geiger Counters are having the "check source" removed before they are allowed to be sold. Madness? Perhaps, but it doesn't hold a candle to what DHS is doing, pushing for this kind of law!
In addition to potential problems with the GM tube (broken/crushed/missing), there are also potential problems with the circuitry inside the device. While it's a relatively "simple" circuit, and schematics are fairly easy to find via mailing list mentioned above (and a sister list, the name of which escapes me, which I haven't looked at in a while), there are "issues."
Apart from the problem of calibrating a GC (or Survey Meter) -- something that can only be done by a licensed lab (which has genuinely hazardous materials, needed to test the different ranges on the devices) -- there are potential problems such as a damaged galvanometer (like all similar meters -- everything from a classic (pre-digital) light meter, to a (pre-digital) VOM -- the galvanometer is fairly delicate, and not too difficult to damage via shock/impact, or by passing too much current through it, i.e., if something goes wrong with the circuit, and it blasts the galvanometer).
Another potential problem is the germanium transistor used to step up the "D-Cell" voltage to the several hundred volts necessary to charge the GM tube. This type of circuit is fairly simple, it's like the circuit in your electronic flash unit -- the thing that makes a faintly audible whine as it recycles between pictures -- an oscillator and step-up transformer -- however, these are OLD devices, old enough that they were built before the proliferation of silicon transistors. Instead, they used germanium transistors.
Germanium transistors are favored for things like guitar "fuzz box" devices, because they have different characteristics (different from silicon transistors). One of these differences is that silicon transistors are MUCH more rugged. Another way of looking at it is that germanium transistors are much more delicate.
Since it seems that no one manufactures germanium transistors anymore, you REALLY want to buy a functioning unit, or, one with a good "DOA" policy. And by "good", I mean that you don't want to find yourself in a position in which you are faced with the proposition of losing more than the value of the device due to multiple/exhorbitant "shipping and handling" charges. Some sellers will offer you a very low price on the item, and then hit you with a very steep "S&H" charge. If you need to return it, he may (quite likely, "will") require you to aborb the initital fee, cover the return fee, and, quite possibly cover the fee on a replacement unit (if he replaces rather than refunds).
Even without a replacement -- with just a straight return for refund -- it's NOT at all outside the realm of possibility to find yourself faced with having to pay more for two-way shipping than you'll get in his "refund" check. Clearly, it would make no sense to "return the defective item for refund" -- your only real option is to grit your teeth and "eat the loss."
This is more long-winded than I'd intended, but the sad reality is that it is VERY easy to get ripped off when trying to buy a "Geiger Counter" when you do NOT know the facts spelled out above. Since your LIFE (and the lives of your loved ones) may depend on this purchase, I don't feel too bad about typing all this crap. :)
I would strongly urge you to either read the archives on the list (URL above) and then, if you have further questions, subscribe, and ask them of the people there (many of them are true experts, some work in the industry, or for (*gasp* the government -- but they're hobbyists, and pretty nice folks). Or, find a local "expert" and ask him to help you find a GC. (I mean a real expert, not some nimrod who "knows all about it" and assures you that a "Survey Meter" is "all you need unless you're a real pro" (blah, blah, blah)...)
Last word, I promise: You would be well served to have a decent/inexpensive GC, a decent/inexpensive Survey Meter too (but NOT until you've gotten a GC!), and, a few "dosimeters" (roughly "fountain pen" sized things that sit in your shirt pocket, which you read by holding up to your eye, and viewing a needle. You also need a "charger", which is another little oscillator (similar circuit), but in this case, instead of maintaining voltage in a GC tube, you are putting some high voltage into the sealed dosimeter, in order to zero the needle. The charger has a knob -- you turn the knob until the needle is zeroed, and then you remove the dosimeter from the charger).
The dosimeters come in a couple of different ranges (i.e. "low" and "high" :) and are fairly inexpensive (often only a few bucks on ebay) -- and, they do NOT require a battery to operate. You just charge 'em up, and then periodically take a peek to see how much radiation you have accumulated. However, they're also fairly delicate -- a light tube, with a vacuum, and lots of "stuff" in it -- i.e., the needle mechanism (static electricity holds it in place, radiation zaps the static), a lens for the eyepiece, etc. Lots of places where they MAY develop a leak. A leaky dosimeter is a paperweight.
Basically, you test them by charging, and seeing if A) you can zero them with the charger, and B) they'll hold the charge (i.e., should NOT "wander" off the zero point -- unless you're in a hot zone!)
They should not be thought of as your primary line of defense. They're more like the special "badges" worn by people who work in the Radiology department at a hospital -- something that will show accumulated radiation over time, NOT something that will tell you "how hot is it here?" (In other words, if you are in a known "hot" zone, and you want to limit your exposure (I am not going to go into stuff like REM limits etc. I'm too tired, I'm a bit rusty, and the info is readily available), then you would periodically check your dosimeter to see when it's time to boogie. Sort of like the air gauge on a SCUBA rig.
Any questions? Don't ask ME! :) (Seriously -- I've barely scratched the surface, and I am NOT really qualified to go much beyond what I've posted here. The main point I cannot overemphasize is to NOT buy a "Survey Meter" thinking that it's a "Geiger Counter" -- and I emphasize it because this mistake is made ALL too frequently, in part due to people not knowing what they're buying, in part due to some sellers not knowing what they're selling, and, in part due to SOME sellers who DO know what they're selling (!!!) going right ahead and foisting these things on the unwary. Thus, I close as I began, CAVEAT EMPTOR!
PS: It's NOT often that I sit and type out a message of this length. NONE of this is boilerplate. I typed out the entire thing from scratch, in real time. I did this because it is IMPORTANT information. I only hope that the TYPE of importance never goes beyond the "don't get ripped off" realm. Unfortunately, in the world we live in, we'd be fools to NOT consider the possibility of "the unthinkable" hitting us. For those who think this to be a stretch, click on my name, go to my FR home page, and scroll down to the "Night of the Weak Knees" excerpt.
If you won't believe me, maybe you'll believe Christopher Hitchens.
Oh, boy.
It’s worse than I thought.
Not only is DHS behind this, but, they want to use it as model legislation for the rest of the country.
Where’s the outrage? Where’s the NEWS coverage? (So far, the Village Voice and one Op-Ed in the NYT seems to be it! Hey, Rupert — can’t you cut at least a minute or two from the nonstop celebrity gossip BS “news”, and endless babbling about the endless polls that no one gives a damn about — to devote to coverage of a REAL story?)
Read, contemplate the implications, and feel ill:
http://www.nytimes.com/2008/01/30/opinion/30omullan.html?_r=1&oref=slogin
That's putting it mildly, but I agree.
Howevever, if you want something really portable, that can warn you of dangerous radiation levels, get a device called a NUKALERT. It is small enough to hang on a key chain (my wife keeps hers there; I keep mine in my pocket), and gives you a rough measure of radiation level. Good enough to tell whether "it's safe to go out yet."
Incidentally, building a GM counter isn't all that easy. I tried it when I was in high school, back in 1949. The electronic circuit isn't all that hard, not even with vacuum tubes. It's simply a trigger circuit that takes pulses from the GM tube and converts them into square waves. Building the GM tube itself is really difficult. My several efforts weren't good enough. Evacuating and sealing the tube is tough unless you have industrial-grade equipment.
Your thoughtfullness is just another example of why I love this site. Thanks.
Molon Labe.
I have one.
Aware Electronics sells an assortment of very inexpensive geiger counters, their cheapest is the RM-60 at $150. It can be hooked to a cheap PC to run software (provided) to graph the readings.
Idiots.
It's one thing to be able to detect a hazardous level of exposure, but then what? I'm surprised you mentioned the need to buy all that stuff without pointing out that having plenty of potassium iodide on hand reduces the risk associated with some types of radiation exposure.
It's sure cheaper than a geiger counter and is a necessary part of any radiation disaster management plan.
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