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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!"
In case you didn't know what it was (like me):
Wikipedia:
A Geiger counter, also called a Geiger-Müller counter, is a type of particle detector that measures ionizing radiation. They detect the emission of nuclear radiation: alpha particles, beta particles or gamma rays. A Geiger counter detects radiation by ionization produced in a low-pressure gas in a Geiger-Müller tube. Each particle detected produces a pulse of current, but the Geiger counter cannot distinguish the energy of the source particles. Geiger counters are popular instruments used for measurements in health physics, industry, geology and other fields, because they can be made with simple electronic circuits.
Carl Sagan quotes get you an automatic +5 on all posts.
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.
"Have you ever thought about just turning off the TV, sitting down with your kids, and hitting them?"
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.
test G counters with a mantle for a gas lantern, like Colman. it's a strong short range source, so when you hold it an inch or 2 away, it'll be loud. anything thats that loud, worry about. less than that, don't worry about. That's what I learned in a Nuke Med R&D/mfg facility.
Well, perhaps an Ionization type detector, but probably not other types, like Optical.
It must have been something you assimilated. . . .
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--
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 $$$$).
I have a Geiger counter from the 1960's that includes a small sample of radioactive material on its side for testing and calibration. The manual states that there should be a certain number of clicks per second, and based on the half life of the material, it looks like it still works fine. Amazon also sells small samples of uranium that have a specific number of clicks per second that you can use to test your equipment.
Other than that, there is a normal level of background radiation that amounts to about 14 clicks per minute if no other material is available, but this might not be viable in your area.
Actually, I don't really have a pressing need for my Geiger counter, and it sure sounds like you need it more than me. If you want, I'd be happy to ship it. Let me know.
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.
I can't say anything about calibrating, but an easy way to check it's functionality and great way to demonstrate science is as follows:
:)
Go outside, preferably during the day, take a reading. This is background radiation, you live in it your entire life, it varies, and the sun puts out a lot so it will be lower during the night. Don't panic, Hollywood, like usual, got the science wrong. (Think about it, how often do cars actually explode in real life. Yeah, Hollywood science is useless.)
Great, now go inside a building, take another reading. If you've got access to a nice sturdy concrete building with a basement, or some caves, those are even better. See how much it dropped? That's because of the building (or earth and solid rock) blocking the radiation coming from the sky.
Now keeping an eye on the changing levels is probably what someone in Japan really wants, but you might have to ask someone that's in the science department at a university to find out what the readings were before the Fukishima incident.
Also, distance from source will effect intensity by a lot! So a chunk of radioactive material 1 meter away will read much much higher than one 10 meters away. Since the sun and other stars are so far away, the measly distance of the Earths diameter won't make much different to those, so unless there's a flare or something, only the terrestrial sources will be a big worry.
Anyhow, this is all high school stuff, or it used to be before they started dumbing down science in schools, so it's easy to find books about it in most libraries.
As a side note, you can NOT detect a modern unexploded nuke with a geiger counter, their cases are so heavily shielded you can use them for radiation shielding.
Again, Hollywood is so full of it.
"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.
if you know somebody who organizes a lab course in physics, in a university you can ask if you can take the geiger counter there and compare it to their calibrated samples. Typically there is a box of sealed test samples (well locked away), which have well defined radiation doses in different gamma-ranges, so you can test the sensitivity. However, you will have to take an safety instruction to even touch the box. So if you know somebody there well, he may help you. He may even tell you how to calibrate the device correctly using that sample. Another way, which is less technically challenging and will not give you a quantitative calibration is to use one of the typical stones which radiate stronger. Refer to any standard textbook which these are in you region. Look e.g. for granite on wikipedia and follow to the original sources. However none of these means will provide you with any information about the sensitivity of the counter.
As for your friend trying to measure food: More than a quantitative comparison "this radiates stronger than that" will not be possible. The data will be problematically low for the prescribed doses if the counter has no good integrator/long term counter and is stable. Any quantitative measurement of contamination with isotopes is completely unrealistic outside the lab and with an inexperienced operator, especially if the device has no energy resolution. A simple workaround around the latter would be insert materials with different absorption coefficients into the path and compare the measurements, but i cant tell how well that works. Moreover 100-1000Bq/kg is not much. I doubt you manage to get more than a count rate of 1-10clicks per second from a sample of acceptable size. which means that in order to get a 10Percent resolution you may have to integrate over 100seconds or more. That means that the dark count rate should be acceptably stable.
If your friend does this to protect the own health, i recommend the following: don't do it. There are two possibilities: either the food in monitored professionally and marked correctly (which i believe is normally the case in Japan) or its not. If its monitored professionally then there will be no long-term contamination which is undetected. The effect of a spurious peak in one meal to ten or even hundred times of the allowed level wont kill you or have any adverse effects, and reliably i think you will be only able to detect starting from about 10-100 times of the allowed dose. If the food which is not monitored professionally *and* comes from within 50-100km around the reactor then don't eat it, if you have the choice, until the situation stabilized (that is, when any kind of containment, even by a simple plastic foil is reestablished and then after a few months, look at the ieae website). If you believe you must support the farmers there, then donate money, don't buy the food.
An non-reading can also provide you with a false sense of safety, and that is true for all uncontrolled foods. There is no way for a layman to establish safety of a food which comes from within the problematic range around the reactor.
My personal feeling is that *in Japan, which has high food quality in general* an inexperienced operator of a Geiger counter trying to measure his own food will have higher stress due to mis/unclear readings and the constant (lets remember, this may have to be done for 20years if you take it seriously) reminder of the danger just before eating. The adverse health effects of this and possible associated psychological effects (stress before eating) will outweigh the negative effects of getting a higher dose from time to time. If you take the 30min-1h per day which you need to check the food *seriously* for such low doses of radiation, then there are other thing you can do in this hour (go jogging, ride a bike etc.) which will help the body more to develop the immune system.
If I remember correctly the reported levels of contamination in the food and water supply in Japan were, even at their peek, in the order of a couple of 100Bq per kg. You need to put a sample in a counter or spectrometer for some time to be able to tell those levels from background. Pointing a GM tube at pieces of spinach to see if one is contaminated more than another is futile, all you are going to notice is variations in background. You can have fun finding all sorts of slightly radioactive things with a counter if you like but unless you are willing to spend >$10k on a portable gamma spectrometer which _might_ be able to distinguish tiny amounts of I-131 or Cs-137 from background you are not going to find anything in the food.
Vaseline is radioactive?! So you're saying I shouldn't be using it to, you know, wax my carrot?
There's no -1 for "I don't get it."
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.
Contrary to the popular belief, there indeed is no God.
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.
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).
... 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).
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
Thanks for all the excellent input and we will be reviewing it throughly.
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.
If you really need two, I have some. want much and if it would like them pm me. I have them on Craigslist in Dallas. I would rather help a fellow slashdotter. They were always calibrated, but the cal sticker ran out last year. Just pm me.
If you want a cheap radiation source, you can buy 2% thoriated tungsten rods for TIG welding. Find a local store and buy a 1/16" rod: individually they only cost about $8. Other people have suggested Coleman lantern mantles but the ones you can buy these days don't seem to have thorium in them anymore, because the old ones were *seriously* radioactive. If you *have* a Geiger counter you can go to an Army/Navy Surplus store and check the ones they have since a lot of old radioactive ones are still in stock.
My homebuilt geiger counter, using a surplus Russian GM tube, can easily detect a single thoriated tungsten rod if held up close to the tube, as can my vintage Civil Defense CDV700. Both will also detect a smoke detector.
If you want to build your own geiger counter and have a tube, here are instructions for building a high voltage power supply from a hacked-up flash unit from a disposable camera and here is the detector circuit that translates that into audible clicks. If you optoisolate that detector circuit you can feed it into an Arduino and log/display counts per second on a laptop. (It needs optoisolation because the output of the audio click board is negative with respect to power and way more than 5V, so it'll cook an Arduino, as I found out. Although an Arduino analog input can withstand -200V and still function, amazingly enough.)
If you just want to detect ionizing radiation, you can build an ionization chamber. My company supplies DIY kits but we also have detailed instructions for making your own with a component list of like four transistors and a handful of resistors, and a tin can. They're more sensitive than a Geiger tube, although they're much slower to react, taking seconds to change their reading. One neat thing is you can build them as chambers so you can actually put a sample inside the chamber, if you want, and they detect alpha, beta, and gamma.
And as other people have said, any sample you buy that'll allow you to characterize your radiation detector will expose you to tens to thousands of times as much radiation as anything in Japan unless you're actually inside the grounds of the power plant, so this whole project might not do what you want.
Nostalgia's not what it used to be.