Testing Geiger Counters

thesandbender writes "My girlfriend's family lives in Japan and is very interested in obtaining geiger counters for testing food and other materials. Geiger counters are now impossible to get in Japan and are on long back order from most providers in the U.S. which makes me suspicious of anything we can get our hands on. My question is, what's the best way to test/verify a geiger counter. I know I can point it at a smoke detector and it should go off but I'm not sure what I should see on the gauge. We'd even take it to any reasonable local facilities for testing (NYC area). Any input would be greatly appreciated!"

Comments

Vaseline glass.

[Kenja]

A common way to test a Geiger counter is to use a small sample of Vaseline glass such as a bead. The glass contains a small amount of uranium oxide which should be detectable.

Re:Vaseline glass.

[Kenja]

As I said, Vaseline glass is often used as a calibration source. The CPM for many sources and quantities is well documented. True, if you get a random piece off eBay for a few dollars you may not know what its reading is supposed to be, but it should be consistant between different devices.

Re:Vaseline glass.

[Kalidor]

Or rather, they should at least give you what various safety levels are. One of the big misconceptions is that we know what is a dangerous level of radiation: in fact all we know is what is too much radiation. Back in the 50's and 60's a group of scientist were asked to provide safety information on radiation and they came up with a scale using the points of zero and you aren't gonna see the end of the week. They then drew a linear line between these points because they had little to go on, and presented it as a best guess and further research was needed to prove it's truly linear, exponential, logarithmic, or what-have-you. Since then the linear graph has become kind of dogma and various groups have picked various points across it to set their safety thresholds.

You'll find that you have a set threshold in most Asian nations that is quite low, due to close experience and some might say paranoia in relation to the deployment of nuclear arms.
Roughly double these guidelines, and you get what is considered safe in many European countries.
Roughly double them once more, and now you are heading toward the Americas.
 

Re:Vaseline glass.

[Lefty2446]

After rereading this a couple of times I really have to ask for confirmation :

So :
* "by convention", 1 mSv/year is considered "safe"
* the location you live in outputs about 3 times that value (natural source)

But, because we "know" where it comes from, and because it's "natural" radiation, it doesn't count as being harmfull and the safety limit is upped to those 3 mSv/year PLUS the "by convention" 1 mSv/year ??

??? What kind of logic is that ???

Shouldn't they just put the limit to 3 mSv/year for all people living in that area ? (it's kind of non-practical to remove all background radiation) + pay extra attention to potential effects due to already having 3 times the 'conventional' limit to live with ?

So nobody who lives in that area qualifies for X-rays, scans etc?

I know the following is XKCD but it's still quite informative:
http://blog.xkcd.com/2011/03/19/radiation-chart/

Re:Vaseline glass.

[umghhh]

The question about what is a safe level is a really tricky one especially as it involves statistics i.e. it is usually not: if you cross this line you will be shot but rather if you cross this line you may shorten your life by this much or become a customer of cancer clinic in course of your life but that you can also without additional exposure. There are different people and different effects depending also which part of the body got hit the most. On top of it if certain radioactive materials get into your body the effects depend on what these were and which part of the body is affected the most. Plutonium is highly toxic by itself and getting already small amounts into your system will probably kill you or made you uncomfortable (as with kidneys' failure uncomfortable for instance). On top of it you have empirical data from people working with extreme levels of radiations and these are not straight forward either - members of army units that cleaned up the shit in Chernobyl are mostly dead by now and those living are mostly sick yet President Carter took part in similarly adventures operation in Canada at Chalk River Laboratories in 1952 and he is still well.

I guess the bottom line is that you just need to ensure thatbloody thing is working in the first place i.e. shows something and then compare the results - assuming majority of the food stuffs are safe then measure those and see whether there is change.

Don't get one.

[Anonymous Coward]

99% of the general population can't operate one. Measuring radiation is not like measuring signal strength of an electromagnetic field. People forget that it's radioactivate _matter_ emitting radioactivity, something akin as if you had tiny mobile towers all over the place. There is a large difference between a weak emitter stuck to your geiger counter and a powerful source a lot further away, but radioactivity-wise at a specific point they are indistinguishable. There is a large difference between different kinds of radioactivity aswell.

Geiger counters are useless for someone without at least a basic education in nuclear physics.

Re:Don't get one.

[the_raptor]

Unless you are picking lettuce from the grounds of the Fukushima nuclear power plant that scenario isn't going to happen (and anyway you should ALWAYS wash produce, the pesticides etc that get used aren't exactly great for you either).

From what I have read the fallout is at such low levels that it is within the bounds of variation in background radiation (ie mostly the levels are below what you would get from living in a high altitude area like Denver, Colorado). Unless you are in the immediate vicinity of the leaking reactors you aren't going to get a dose that has immediate effects, and just ignoring the whole situation will cause less damage then regularly eating junk food.

People in general are fucking terrible at risk assessment, and that is before you use the word "radiation".

There are several different types of radiation detectors with varying degrees of accuracy, and the type you can scrounge around and get now are probably not worth the money even if you put in the time and effort to calibrate and understand it.

Re:Don't get one.

[DDLKermit007]

No, not really, Geiger Counters are honestly something not meant for public use. If their family is that freaked out about the radiation, and don't trust the government, they need to jump ship like all the other weird foreigners that panic instead of being selfish and gobbling up the supply of Geiger Counters officials could be snatching up. Unless they are getting food that was raised next to the reactors, the dosage is going to be laughable. They'll get more radiation on their flight back to the states than from any ammount of cumulative food they are going to eat. Morons the whole lot of them.

Some types of smoke detectors.

[fahrbot-bot]

I know I can point it at a smoke detector and it should go off ...

Well, perhaps an Ionization type detector, but probably not other types, like Optical.

DIY

[Anonymous Coward]

If Geiger counters are hard to buy, you can make one. Here's an absolutely brilliant video on how to:
http://www.youtube.com/watch?v=G6Q7VfWdgEg

The basic idea, and brilliance, is simple. Get a plastic scintillator and hook it up to a CCD camera. Use a time exposure to record the flashes of light, and you have a cheap and easy Geiger counter. Suitable for checking food, as well as getting an idea for the radiation around you. It's not as immediate as a real Geiger counter, but at least you have some way of seeing what's going on around you instead of being blind. The scintillators are a little hard to get retail, but very available on eBay. Cost is cheap. About $32 for a 2x2" square (which is overkill). And a simple test here is to just buy a bunch of bananas, which are naturally radioactive, though very low level.

The next step up is to add some electronics. The NukAlert is great here. Japanese customers can find it at:
http://www.nukalert.jp/

I have no association with nukalert.com other than as a satisfied customer. I also don't read Japanese, so I have no idea as to what it says.

Now, to test these suckers out, you need actual radiation. You can get low level radiation devices in the States, 5 uCurie Cs-137 sources for about $80. These are used to calibrate various instruments. I would imagine that there is a way also in Japan, given how much equipment is built there. But I'm not sure if these can be imported.

HTH.

--ES--

Re:DIY

[maxwell demon]

If Geiger counters are hard to buy, you can make one. Here's an absolutely brilliant video on how to:
http://www.youtube.com/watch?v=G6Q7VfWdgEg

The basic idea, and brilliance, is simple. Get a plastic scintillator and hook it up to a CCD camera. Use a time exposure to record the flashes of light, and you have a cheap and easy Geiger counter.

That's a radiation detector, but it's not a Geiger counter.

Of course, what the poster wants most probably is just a radiation detector (and the Geiger counter is just the one radiation detector he knows of), so your advice isn't wrong; it's just wrong to call that a Geiger counter.

Geiger counters are not really useful

[Cyberax]

Geiger counters are not really useful for food testing. They generally won't detect alpha radiation which is the most harmful type. Besides, elevated concentration of caesium or strontium can be easily mimicked by elevated levels of natural K-40.

They really need to stop worrying about food testing. Or get a professional radiometer (which will cost $$$$).

Re:Geiger counters are not really useful

[antifoidulus]

But are they useful for testing radiation levels in the air? I live less than 100km from the edge of the evacuation zone and really would like to go there by bicycle(almost impossible to get in by car because they have barricaded off most of the area, but from what people have said, it's pretty easy to sneak in on foot or cycle). How much risk would I actually be exposing myself too? Also, would a geiger counter help?

Re:Geiger counters are not really useful

[Cyberax]

For outdoor testing Geiger counters should work just fine. You don't need to worry (much) about alpha radiation, if you are careful to not eat or drink anything from the contaminated zone and wash your clothes and shoes afterwards. Also, try to avoid dust.

You won't encounter promptly dangerous radiation levels, even if you are near the powerplant itself. Even doses as high as 100 times the normal background level require _months_ of exposure to become dangerous, and these kinds of doses will cause Geiger counter to click continuously.

Maybe I'll go for some karma too:

[Chrisq]

But, for him to be karma whoring, there'd also have to be a significant number of slashdotters who don't know (which is quite the unlikely case). So, either he didn't know; or he over-estimated the number of slashdotters who don't know.

Arse:
1. the buttocks
2. the anus
3. a stupid person; fool

Elbow:
1. The joint or bend of the arm between the forearm and the upper arm.
2. The bony outer projection of this joint.

Well its about ask likely as a slashdotter not knowing what a Geiger counter is.

Use calibrated radiation sources

[goodmanj]

"Point it at a smoke detector" won't work: the americium in smoke detectors emits alpha radiation, which can't penetrate the walls of the detector. There's no sense messing around here: if you want to do it, do it right. You will need a little bit of money and the ability to do math.

Buy a calibrated radiation source: you can buy them here, among other places. They're relatively cheap -- tens of dollars. Cs137 is very easy to get, but you also might want to get some Sr90, which is a pure beta emitter. These sealed disks contain such a tiny amount of radioactive material that the risk to health from them is negligible, and they can be mailed and used without a license. However, I do not know mailing them internationally is legal or wise.

(The same company will also sell you a lead container to hold your sources in, but I'll tell you from personal experience that quite a few gamma rays will go right through the container.)

Put the source in front of the detector, a short distance away. If your detector is working, it should start clicking/beeping like crazy. Calculate the count rate. By working out the geometry, looking up the properties of your source, and converting curies to counts per second (hey, nobody said this would be easy), you can work out the "efficiency" of the detector. Move the source farther from the detector: the counts should fall off as an inverse square law.

Now that the detector is calibrated, you can use that efficiency factor to calculate the radioactivity of an *unknown* source.

Important note: while these sources are generally considered safe, the radiation they emit will be *many* orders of magnitude more than any contamination in Japanese food products. You can look at this fact in two ways: either this shows that concerns about food safety are overblown, or suggests that the best way to protect yourself from unnecessary radiation is to not do this experiment.

If you don't have access to or don't want to buy calibrated radiation sources, you can buy yourself some "No Salt" salt substitute, which is food-grade potassium chloride. The naturally radioactive potassium-40 in it is easily detectable with a good Geiger counter: you can look up the natural abundance of 40K and do a little chemistry to figure out the number of curies in a carefully measured gram of KCl, and use it as a calibration standard.

Re:Use calibrated radiation sources

[kf6auf]

Look up Americium in a Table of Isotopes; there are a decent number gamma rays that it emits at 60keV or 73keV depending on the isotope (Am-241 or Am-243) after it alpha decays. That said, smoke detectors vary a lot depending on the amount of Americium inside and you're always better off with a long half-life calibration source.

Re:Use calibrated radiation sources

[the_raptor]

'"Point it at a smoke detector" won't work: the americium in smoke detectors emits alpha radiation, which can't penetrate the walls of the detector.'

When I was in high school 12 years ago the radiation sources the science department had were from the 80's and barely registered above background using the Geiger counter we had. I bought in some Americium based smoke detectors from home and those where emitting massively more amounts of radiation.

It is my understanding that the alpha from those sources would be stopped by the plastic housing and a few centimetres of air, not by the ionization chamber housing itself.

Wait, what?

[MrEricSir]

Vaseline is radioactive?! So you're saying I shouldn't be using it to, you know, wax my carrot?

Re:A tiny bit on radiation readings

[Teun]

You are very wrong in assuming radiation is less inside a building, especially granite has a high natural radiation and it might be incorporated in the concrete.

Certain kinds of plaster board are made from material recovered at cement furnaces and it too has a quite high radiation level.

Radiation measurements are part of my job, I'm certified for it and I can tell you making a useful measurement of foodstuff requires expensive gear and a lot of time.

A simple way of checking the counter is to point it downwards to a non-polluted part of the ground, record the reading in counts/sec, this is called the background radiation.

Background radiation is as low as 4-8 counts at sea and around 30-40 in an area with clay or granite. Going up in the mountains might expose you to ~100 counts/sec from cosmic radiation. Now point it at the object you want to check, when the reading is less than 3x the background it can be considered non-polluted. That doesn't mean it's safe but at least there's less worry.

The biggest problem is these meters will not show you all radiation, usually only Gamma and Beta radiation while Alpha can be just as dangerous. Some sorts of radiation have a hard time passing through even a thin layer of moisture, that includes the skin of vegetables.

All in all, buying a Geiger counter is most likely a total waste of money and certainly a source of misinterpretation.

Don't.

[Alex Belits]

geiger counters for testing food and other materials

Geiger counters are absolutely useless for testing anything other than minerals, background radiation and things like ventilation ducts (surprisingly a major collector of everything radioactive). After Chernobyl disaster I made, used and later calibrated a simple Geiger-counter-based ionizing radiation meter, and it was useful to determine how contaminated the areas around my city (Gomel) were. The result was exactly the same as what was confirmed later -- some short-lived contamination within the city (easily attributable to I-131 due to distinctive half-life around a week), mostly clean to the southwest, more contamination (longer-lived, counter was useless for determining its nature but later I have learned that it was Sr-90, Cs-134 and Cs-137) to the northeast.

However to test anything that even resembles food, you need a gamma spectrometer, complete with a test chamber made of lead bricks. I happened to participate in those measurements much later, and I am certain, Japanese environmental/food safety authorities are already using something similar now. You have absolutely no chance to get anything close to it on your own, so just don't.

Re:Don't.

[Attila the Bun]

You have absolutely no chance to get anything close to it on your own, so just don't.

I'm afraid this is pretty much true, although the hobbyist in me doesn't like to admit it.

The amount of radioactivity you're looking for is small compared to natural background, and small even compared to the normal variations in background. To identify any un-natural contamination you'll need a detector capable of distinguishing different isotopes, in a low-background environment, and it'll need to be regularly calibrated with standard sources. That entails a lot more gear than a Geiger-Muller tube, all of which is very very expensive, not to say tricky to operate.

With a GM counter about the best you can do is to try to measure the radioactive decay of a sample, although most relevant isotopes have very long lifetimes which will be too hard to measure. 131-iodine is easy to detect and has a measurable half-life at 8 days, but I expect the authorities would find it before you do, and anyway most of it has gone by now.

Alternatively you might befriend a physicist at your nearest nuclear research institute. Even then he or she will need to be quite a good friend, because the time and effort involved is significant, and this kind of expensive gear tends to be permanently in-use.

Regular salt - it contains potassium-40

[pepax]

Use common kitchen salt (NaCl). It contains a small amount of potassium chloride (KCl). The amount of KCl in the salt you buy should be listed on the packaging. 0.012% of the KCl present will contain a naturally occurring radioactive isotope of potassium, potassium-40 (half-life of 1.3 billion years). So, if you weigh the amount of salt you test with your Geiger counter, you should be able to figure out how much potassium-40 you have. The specific activity of potassium-40 is 0.0000071 Curie/gram. One Curie is 3.7×10^10 decays per second, so one gram of potassium-40 should give you 263000 decays per second, one milligram of potassium-40 should give you 263 decays/second, and so on. By comparing your measurement results to what you would expect, you can tell how well your Geiger counter is performing. Be ready to measure for at least several minutes, though.

Re:Regular salt - it contains potassium-40

[arisvega]

one milligram of potassium-40 should give you 263 decays/second, and so on.

You have a good idea there but all these are rough estimates. The actual counts would depend on the distance from the source (in effect the solid angle), the instrument's sensitivity, the source's geometry and other stuff I may be forgetting.

I have done instrument calibration (as a student, not as a lab manager, so I am not an expert by far) on both Geiger-Müller counters and solid state detectors. Calibration was mandatory before the actual measurements took place. Even in laboratory conditions, with experts running around and helping out, point sources and 0.5mm accuracy on distances and the like, let's just say that they turned out to be not the easiest instruments to use, and people where ending up being off (but not way off) in their estimates for the actual activity of the radioactive sources.

Furthermore, there are different 'types' of 'radiation'- alpha, beta, gamma, neutrons. Depending on your counter/instrument, you could measure on or more of these; also there is math to be done afterwards; some instruments (like G/M) measure just 'counts' (the event when a particle 'hits' the detector), others can give more detail. And you need to do some math afterwards, unless the instrument itself does it for you.

My punchline; its use is not trivial, it needs some training (not impossible, though). In times of need such as these I would assume that the few instruments that find their way to Japan would be put to much much better use if they are delivered to experts.

Re:Regular salt - it contains potassium-40

[Anonymous Coward]

This is probably below detection limits -- not because of the sensitivity of typical Geiger counters isn't theoretically able to detect that, but because background sources from all around you will contribute too, and 0.012% 40K in whatever KCl is in table salt is nothing by comparison to those. The signal will be swamped. With a real Geiger counter set at high sensitivity, you'll hear a steady peck-peck-peck of radioactive particles from the environment. With a high enough sensitivity, it will be a steady buzz. If I take a typical granite or clay sample, which contain many times more K than in table salt (up to several weight percent), it can sometimes still be difficult to differentiate them from background with any Geiger counter I've used, like this old classic. 40K has a fairly slow decay rate too (a half-life of ~1.250 billion years), but if you get pure KCl, it is probably detectable.

Many Geiger counters come with their own radiation source for calibration purposes, although obviously they wear out with time due to decay. I'd say if you don't get a calibration source with your Geiger counter purchase, then it probably isn't a very good one, because you have no way of verifying that it is working.

Also, be aware that while Geiger counters detect gamma rays, they don't detect beta rays unless they have the right window over the tube, and it is unusual for them to detect alpha radiation at all unless they've been geared up with a special probe. Furthermore, it is very unlikely that you could reliably test for potential food contamination of any significance with an ordinary Geiger counter without careful laboratory calibration of both the instrument and the materials you are testing (i.e. food samples that are "known to be non-radioactive"). A Geiger counter tells you "it's hot" to varying degrees. It probably won't be able to tell the difference between an ordinary uncontaminated banana (plenty of K) and a contaminated cucumber, or maybe even the difference between cucumbers grown in different soil nutrients or with a little bit of clay on them. There is going to be a lot of natural variation between foods. We're talking about vanishingly small amounts of radioactive material, and trying to differentiate those from background isn't easy. To do anything useful you probably need an instrument tuned to the particular gamma ray frequencies of the isotopes that are greatest biological concern, such as isotopes of iodine, cesium, and strontium.

Unless you know you're buying and eating food from within the contaminated region (for some strange reason), the best bet is probably to trust the Japanese food inspectors and to wash food thoroughly. Self-measurement of food for potential contamination by radioactive materials is likely to be an exercise in frustration with a regular Geiger counter.

Re:Geiger Counter

[Anonymous Coward]

I can't believe so many people are doubting if slashdotters know what a Geiger Counter is when the original question begins with "My girlfriend's family". That means he's wondering if his Japanese Real Doll (Leal Doll -- don't worry, I'm Asian) is safe for sexy time.

If this dolls a clickin'
don't bother dickin'.

Follow up from the author

[thesandbender]

1. I appreciate everyone's input about the comparative levels of radiation and I'm working with my g/f to translate the xkcd chart to Japanese to put things in perspective for her family (we'll be sending it to Mr. Munroe when we finish for him to post if he likes).
2. We've already purchased Vaseline glass beads.
3. I'm very interested in the detailed comments that testing is pointless b/c we couldn't get access to the equipment/environment needed to properly test and will be following those up.

From a practical and scientific standpoint we both understand that the exposure they are subject to where they live is less than being at altitude on a flight to Japan. However her family and the country as a whole has been through a very traumatic event ... first from a force they can't predict (the earthquake) and now from one they can't really see (radioactive contamination). So why we can look at this objectively and say the exposure really doesn't amount to much unless you're near the site, they'll never be able to because of what they have been through. Realistically, if you survived a plane crash you'd probably be hesitant about getting on a plane even though the statistical chances of you being in two commercial plane crashes are practically 0. Just the way the human psyche works. Anyway, I would like to keep them from throwing money away if testing food is a complete impracticality (#3).

Thanks for all the excellent input and we will be reviewing it throughly.

How to test a geiger counter -- READ THIS

[Proudrooster]

First off, a smoke detector is not a good source for testing a geiger counter. The high voltage gas canister inside is usually tuned for Cesium and Americium (the source in a smoke detector) usually gives a false high reading.

To test properly, you need a known source. The better counters come with a source, usually taped to the side of the unit, but you can get sources off of Ebay.
http://cgi.ebay.com/Radioactive-Mantle-Geiger-Counter-Detector-Test-Source-/160587370187?pt=LH_DefaultDomain_0&hash=item2563c0cecb

I don't have much time this morning, so here is an excerpt from my radiation monitor manual for how it works and what it detects. Good luck.

How the Radiation Monitor Works The Radiation Monitor senses ionizing radiation by means of a Geiger-Mueller (GM) tube. The tube is fully enclosed inside the instrument. When ionizing radiation or a particle strikes the tube, it is sensed electronically and monitored by its own display, a computer, or by a flashing count light. When the switch is in the AUDIO position, the instrument will also beep with each ionizing event. It is calibrated for Cesium-137, but also serves as an excellent indicator of relative intensities for other sources of ionizing radiation. Gamma radiation is measured in milli-Roentgens per hour. Alpha and beta are measured in counts/minute (CPM). About 5 to 25 counts at random intervals (depending on location and altitude) can be expected every minute from naturally occurring background radiation. The end of the GM tube has a thin mica window. This mica window is protected by the screen at the end of the sensor. It allows alpha particles to reach the GM tube and be detected. The mica window will also sense low energy beta particles and gamma radiation that cannot penetrate the plastic case or the side of the tube. Note: Some very low energy radiation cannot be detected through the mica window. The Radiation Monitor does not detect neutron, microwave, radio frequency (RF), laser, infrared, or ultraviolet radiation. It is calibrated for Cesium-137, and is most accurate for it and other isotopes of similar energies. Some isotopes it will detect relatively well are cobalt-60, technicium-99m, phosphorus-32, and strontium-90. Some types of radiation are very difficult or impossible for this GM tube to detect. Beta emissions from tritium are too weak to detect using the Radiation Monitor. Americium-241, used in some smoke detectors, can overexcite the GM tube and give an indication of a higher level of radiation than is actually there.