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Testing Geiger Counters 277

Posted by samzenpus
from the rads-are-bad dept.
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!"
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Testing Geiger Counters

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  • Geiger Counter (Score:2, Informative)

    by Palmsie (1550787)

    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 particle

  • Vaseline glass. (Score:5, Informative)

    by Kenja (541830) on Monday May 23, 2011 @02:35AM (#36214602)
    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.
    • They dont just want one to detect radiation, they want one to accurately tell them how much radiation is actually present. They should also know exactly how much radiation is harmful over what period of time. A faulty counter or even poor knowledge of radiation can be just as harmful by underestimating the amount of radiation than by overestimating the amount of radiation and displacing your life / spreading panic among everyone else.

      • Re:Vaseline glass. (Score:5, Informative)

        by Kenja (541830) on Monday May 23, 2011 @02:47AM (#36214676)
        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. (Score:5, Interesting)

        by Kalidor (94097) on Monday May 23, 2011 @02:56AM (#36214720) Homepage

        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.
         

        • Probably the bigger problem is that(outside of relatively few, exotic, situations where the ionizing radiation is sufficiently intense to have you puking out your guts by lunchtime) the bigger question is often whether you are merely being exposed to radiation(modest uptick in longterm cancer risk, risk stops accruing when you leave, basically only x, gamma, and the more can-do beta rays need apply) or radioactive particles(alpha emitters get to come to the party, many radioactive materials are also chemica
    • by SomePgmr (2021234)
      If it's just to see if the thing is working, I've heard a lantern mantle works. Also old radium watches. I'm sure someone can confirm or deny.
    • Wait, what? (Score:4, Funny)

      by MrEricSir (398214) on Monday May 23, 2011 @04:09AM (#36215060) Homepage

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

    • by igny (716218)
      Or you can just go to Area 51 (in Japan Hiroshima or Nagasaki would probably work), test your GC there, compare with values on Wikipedia, update the values on Wikipedia, and you GC is now up to an international standard.
    • by pepax (748182) on Monday May 23, 2011 @06:01AM (#36215480)
      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.
      • by squizzar (1031726)

        That's quite a lot of activity. Which when you have people shouting 'One single piece of ionizing radiation can cause mutations that lead to cancer, we should ban everything nuclear' makes me think that we should all be dead already. It's almost like it's not as bad as those people make out...

        • by Lumpy (12016)

          IF you listen to the nutjobs? yes.
          If you listen to scientists that know what he hell they are talking about.... My rock collection has 2 nice pieces of uranium ore in it. yet the stone walls of my home out out 12X more radiation than the uranium in my basement.

      • by Muad'Dave (255648)

        How about using a salt substitute [wikipedia.org], which is almost pure KCl? That works a lot better. Much higher activity, and the amount of K present is easy to calculate.

      • by arisvega (1414195) on Monday May 23, 2011 @07:45AM (#36215838)

        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: (Score:3, Informative)

        by 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 stea

  • Don't get one. (Score:4, Insightful)

    by Anonymous Coward on Monday May 23, 2011 @02:38AM (#36214622)

    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.

    • by jamesh (87723)

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

      I wouldn't go that far. If you have two cans of beans in front of you and pointing the geiger counter at one gives you the same reading as background and pointing it at the other makes the thing go crazy then I think it's pretty clear which is the safer[1] one to eat.

      Likewise, with a geiger counter it should be easy to tell the difference between a lettuce still full of radioactive fallout and one that's at least been rinsed off :)

      [1] that's 'safer', which doesn't necessarily imply safe...

      • by DrXym (126579)

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

        I wouldn't go that far. If you have two cans of beans in front of you and pointing the geiger counter at one gives you the same reading as background and pointing it at the other makes the thing go crazy then I think it's pretty clear which is the safer[1] one to eat.

        Likewise, with a geiger counter it should be easy to tell the difference between a lettuce still full of radioactive fallout and one that's at least been rinsed off :)

        [1] that's 'safer', which doesn't necessarily imply safe...

        In the former case what is the likelihood of that? Has the food even been canned in an affected region? If so, choose one which wasn't. I assume even if it was then there would be restrictions and possibly an outright ban on contaminated food. In the latter, if the remedy is simply rinsing the food, then rinse the food again. It wouldn't be a bad idea to rinse cans too since it would be dust that is the issue. Also buy foods which are unlikely to be affected by the outbreak, e.g. imported meat & fish

        • by jamesh (87723)

          Also buy foods which are unlikely to be affected by the outbreak, e.g. imported meat & fish & vegetables.

          I think that's the whole point... slapping an "Imported Goods" sticker on something doesn't make it imported, but makes it hard to tell the difference. Do you really trust your supply chain all the way to the end?

          • by DrXym (126579)
            I don't live in Japan and have no idea how their food labelling works. However in the EU all food stuffs display a country of origin and in the case of unprocessed meats, eggs you can usually trace the product right back to the farm the animal was reared on.
            • by mwvdlee (775178)

              So if you stick a copied label on a new egg, has the single chicken retroactively layed double the amount of eggs? Or was the label invalid?

              • by nojayuk (567177)

                The eggs have codes [egginfo.co.uk] printed directly on the shell using inkjet technology. The codes indicate the production facility and the date the egg was collected. This allows an outbreak of, say, salmonella to be traced back to a particular location and even a particular group of birds that laid the infected eggs.

              • by DrXym (126579)
                Eggs are printed with the information of their country / farm of origin, grade, use by date with a red dye. So I expect any fraud involving packaged goods sold through supermarkets would be quickly uncovered. It doesn't stop occasional incidents of dodgy food entering the market but it is usually through dodgy wholesalers selling to fast food places rather than suppliers / supermarkets would tend to be more stringent.
              • by Lumpy (12016)

                the label is magical. the second that label is slapped on something the source is transported to whatever country you wrote on it.

      • Re:Don't get one. (Score:5, Insightful)

        by the_raptor (652941) on Monday May 23, 2011 @03:16AM (#36214828)

        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.

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

        I wouldn't go that far. If you have two cans of beans in front of you and pointing the geiger counter at one gives you the same reading as background and pointing it at the other makes the thing go crazy then I think it's pretty clear which is the safer[1] one to eat.

        Likewise, with a geiger counter it should be easy to tell the difference between a lettuce still full of radioactive fallout and one that's at least been rinsed off :)

        [1] that's 'safer', which doesn't necessarily imply safe...

        Not necessarily - all you know is one is emitting more penetrating particles than the other - whose particles are probably already penetrating your skin as well. The other can could be loaded with alpha emitters which are blocked by the can. Once you eat them, however...

        As a result, your readings don't amount to a hill of beans when it comes to assessing safety...

      • by Lumpy (12016)

        If you put the two cans of beans in front of you, you now have two cans of contaminated beans.
        Again, more than a basic education is needed.

    • Wrong. The goal of the TFA author is simply whether he is entering a potentially dangerous area or if an object is radioactive. He does not need be an expert on the subject to know that if the geiger starts beeping, is because something in place is radioactive enough for him to have to avoid.
  • 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.

  • 1. Your local college/university science department
    2. Local Fire Dept or the nearest Fire Dept hazmat team

    My personal experience is that geiger counters come with a sample for calibration, but apparently yours didn't.

    • by SharpFang (651121)

      Old (esp. military grade) geiger counters came with callibration samples. This doesn't appear to be the case with modern hand-held devices though - they come pre-callibrated and you are not supposed to mess with the callibration in any way.

      One significant reason might be sensitivity. The old ones wouldn't pick background radiation or anything slightly above it. You needed a source just to confirm the device works at all. Nowadays the counters can guage the background quite accurately so you don't need extra

  • by fahrbot-bot (874524) on Monday May 23, 2011 @02:50AM (#36214696)

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

    Well, perhaps an Ionization [wikipedia.org] type detector, but probably not other types, like Optical.

    • Not even then. If your radiation counter goes off near a smoke detector, throw that thing out and get a new one, ASAP!

      Yes, most ionization-type detectors contain a small amount of Americium 241. It is radioactive. BUT... it is housed in a metal can that has angled louvers so that air can pass through, but there is no line-of-sight to the radioactive material. All radiation emitted by the Americium should be (and normally is) fully contained by the can.

      The only way you should be able to measure radiati
  • DIY (Score:5, Interesting)

    by Anonymous Coward on Monday May 23, 2011 @02:53AM (#36214706)

    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 (Score:5, Informative)

      by maxwell demon (590494) on Monday May 23, 2011 @03:16AM (#36214826) Journal

      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 [youtube.com]

      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.

    • by SharpFang (651121)

      The basic idea is brillant. The effect, not quite so.

      Read the comments on the video and follow the links. Plastic scintillator simply does not emit enough light to be captured by a consumer-grade camera. Scientific camera, correct temperature, darkness achieved by thick black plastic - yes, it works. Best of consumer-grade night-vision cameras, 1h exposure - nothing. half-inch plywood appears "transparent" for night streetlights, but the scintillator remains dark. Sources so strong that they make alarm go o

  • by Cyberax (705495) on Monday May 23, 2011 @02:54AM (#36214708)

    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 $$$$).

    • by antifoidulus (807088) on Monday May 23, 2011 @03:11AM (#36214802) Homepage Journal
      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?
      • by Cyberax (705495) on Monday May 23, 2011 @03:24AM (#36214864)

        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.

        • You've convinced me, I'm going to take a brief trip into the evacuation zone as soon as I can. I just have to make sure to post the pictures anonymously as getting caught going in there could potentially get me deported :P
          • by nojayuk (567177)

            A blogger named Spike [wordpress.com] has been to the 20km zone boundary. The Japanese authorities are now enforcing the exclusion zone to prevent looting of deserted properties as well as stopping folks who want to return to their homes.

        • Re: (Score:2, Interesting)

          by SharpFang (651121)

          It's smart to take the counter with you and -learn the doses-.
          The problem is radioactivity occurs in "patches". Places where water drained and dried. Plants that are strongly absorbing. Cloth in the wind, capturing dust particles.

          As for learning the doses: http://xkcd.com/radiation/ [xkcd.com] is helpful but generally, 0.1 microsievert/h is common background level, 1-10 microsieverts/h is the usual "elevarted radiation level" in deserted areas. Some of most radioactive trash in Chernobyl zone findable currently is 3 m

      • 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?

        Not really - you need a device to suck air through a filter and then test the filter. Once you get the counts, wait a while and retest to get the half life and try to see what the source may be.

        • by Muad'Dave (255648)

          Once you get the counts, wait a while and retest to get the half life and try to see what the source may be.

          Often the isotope in question can be determined by the emission spectrum using gamma spectroscopy [wikipedia.org] - no need to wait a half life. If that were true, we'd still be waiting to verify the discovery of most of the isotopes of Uranium and Plutonium.

      • (I) 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).

        Why are you trying to slip past the barricades?

        Do you really want to be asked this question in a Japanese lock-up?

  • 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 [amazon.com] 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
  • by meerling (1487879) on Monday May 23, 2011 @03:08AM (#36214784)
    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. :)
    • by Teun (17872) on Monday May 23, 2011 @04:55AM (#36215242) Homepage
      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.

  • by goodmanj (234846) on Monday May 23, 2011 @03:09AM (#36214788)

    "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 [spectrumtechniques.com], 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.

    • by AmiMoJo (196126)

      mportant 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.

      And here-in lies the problem. Even if you calibrate your Geiger counter the readings will only be assured for much higher levels of radiation than you are likely to encounter. Instruments that can measure very low levels accurately are extremely expensive and require professional calibration. You couldn't just point one at your food either, it would need to be prepared (and destroyed) to get a good reading.

      The good news is that I'm sure there are plenty of people with high end equipment checking food and so

    • by kf6auf (719514) on Monday May 23, 2011 @05:44AM (#36215416)

      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.

    • by the_raptor (652941) on Monday May 23, 2011 @06:26AM (#36215574)

      '"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.

    • Re: (Score:3, Informative)

      by vlm (69642)

      "Point it at a smoke detector" won't work: the americium in smoke detectors emits alpha radiation

      Most of your post is sooo good but this tiny part is soooo far off. I can tell you're quoting some simplified "book learning" not having done experiments in a lab with some Am241 and even a cheapy scintillator MCA. Trust me, you get a nice assortment of gammas from Am-241.

      http://wiki.4hv.org/index.php/Americium-241 [4hv.org]

      Go to google image search, enter "am 241 gamma spectrum" and see pretty graphs of Am241 gamma emission.

      Also, never forget that there is no such thing as a chemically pure (or especially isotope

  • by drolli (522659) on Monday May 23, 2011 @03:22AM (#36214854) Journal

    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.

    • by vlm (69642)

      Been there, done that. Humorously, WRT the NRC exempt samples, the main problem is each source is moderately expensive (think of the cost of a nice lunch). And nuts think it would be funny, cool, scary and 'leet to steal them. So its kind of like walking up to the lab counter in the chem building and asking for a bottle of gold chloride... they probably have it in stock, and they're probably not amused at the idea of "loaning" it to you without leaving behind an ID and signatures blah blah. The main dan

  • 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 wit

  • http://unitednuclear.com/index.php?main_page=index&cPath=2_5 [unitednuclear.com]

    All Isotopes are sold by the microcurie (uCi)
    ( 1 microcurie = 2.22 x 10E6 disintegrations / minute = 2,220,000 cpm )

    Normal sources are + or - 20% pf stated value.
    For calibrated sources, add $120.00 and source will be + or - 5% of stated value and will include a calibration certificate.
    Calibration is only available for gamma sources.

    • by vlm (69642)

      Eeeek, prices have gone up. 20 years ago those sold for about $15 each. I'm not sure if the price of anything but gold, oil, and silver has more than quadrupled since then.

  • by Orgasmatron (8103)

    You can't calibrate it yourself. Or, if you could, you wouldn't be asking here. You need special equipment.

    Look here. http://www.radmeters4u.com/calibrate.htm [radmeters4u.com]

  • http://www.amazon.com/Images-SI-Inc-Uranium-Ore/dp/B000796XXM
  • Use this chart [xkcd.com] and a bushel of bananas.
  • You get a caesium source and measure the radiation level with a known good instrument, and the instrument you want to calibrate. The physics department of any good university should be able to do this. Its a standard prac exercise.

  • 1. Set the scale on as low as possible and watch people freak when the needle pegs ...

    2. When responding to a reported incident, set the scale as high as possible so people feel safe and don't panic since all they hear is a slow tick...tick...

  • Don't. (Score:5, Informative)

    by Alex Belits (437) * on Monday May 23, 2011 @05:54AM (#36215450) Homepage

    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. (Score:4, Interesting)

      by Attila the Bun (952109) on Monday May 23, 2011 @07:14AM (#36215742)

      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.

    • by vlm (69642)

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

      We disagree

      http://tech.groups.yahoo.com/group/GammaSpectrometry [yahoo.com]

  • John Iovine [makezine.com] long time designer/manufacturer of Geiger counters did an interview with Make: about a month ago and his concerns were just the same as yours. There's some interesting insights in the (admittedly short) interview, but it's well worth a read.

    We have a couple of good tube suppliers, because we’ve been in the business for a while. One of them just said to me, “We’ve got shoe makers calling us up, yesterday they were making shoes, and today they want to start making Geiger counters.”

    I know exactly what he was saying. And, really, anybody can make a working Geiger counter. You just put together a high voltage circuit and detect the pulses. But how accurate is it, and what’s its longevity? It took us years to perfect making a Geiger counter—a good Geiger counter. It’s still like a black art. As with a lot of things, you really have to be in it for a while, and see all the crazy things that can happen, and this enables you to can build some resiliency into the circuit so that it will keep functioning properly.

    These people who are just looking to make a quick buck are saying, “I can build a Geiger counter.” Yeah, you can build a Geiger counter, and it will probably work on some level, but you won’t know how to calibrate the thing, or even know that it’s in the ballpark of being accurate.

  • Stop giving into the paranoia and get on with your lives. You're exposed to more radiation on a daily basis than you'll ever get from potentially contaminated food. Nuclear power plant meltdowns may be scary scary, but biological damage due to food contamination is so rare as to be statistically insignificant. If you want to protect your Japanese family, tell them to stop going to restaurants and other public places that allow smoking (which is not only harmful in all the known ways, but is also slightly ra

  • by thesandbender (911391) on Monday May 23, 2011 @06:47AM (#36215650)
    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.
  • http://en.wikipedia.org/wiki/Banana_equivalent_dose [wikipedia.org]

    Found it while I was researching and quantifies what many of you have been pointing out about the effective level of contamination.
  • by Proudrooster (580120) on Monday May 23, 2011 @07:00AM (#36215694) Homepage
    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 [ebay.com]

    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.
  • by WillRobinson (159226) on Monday May 23, 2011 @08:05AM (#36215940) Journal

    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.

  • by smellsofbikes (890263) on Monday May 23, 2011 @11:40AM (#36217978) Journal

    If you want a cheap radiation source, you can buy 2% thoriated tungsten rods [tigdepot.com] 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 [madscientisthut.com] for building a high voltage power supply from a hacked-up flash unit from a disposable camera and here is the detector circuit [madscientisthut.com] 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 [madscientisthut.com] but we also have detailed instructions for making your own [madscientisthut.com] 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.

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