Food Contamination

Since Fukushima, much interest has developed in the application of checking food and water for possible radiation contamination.  Here are your options:  

Rely on government agencies, such as the EPA (Environmental Protection Agency) and the FDA (Food and Drug Administration) in the US, or

Procure the same equipment used by those agencies and conduct your own tests.  These include specialized devices like Multi-Channel Analyzers for Gamma Spectrometry, etc. which are quite thorough and able to detect very low levels of contaminants, along with which isotopes are present.

Or acquire a personal radiation detector which, while not as effective or thorough as the above alternatives, is readily available to the lay person and easy to use.

In the field of radiation detectors, the two most popular designs are Scintillation Counters and Geiger Counters.  Many scintillation counters are more sensitive in general, and able to detect certain radiation at greater ranges.  These devices tend to be more expensive than Geiger counters, and generally larger, more specialized, and less compact in design.

The most popular design of radiation detector is a Geiger counter because it is readily available, easy to use, of compact design in many cases, and in an affordable price range.  And certain models are quite sensitive.  So, for one who chooses to use a Geiger counter to check food and drink for radioactive contamination, certain criteria are recommended:
    

Its Geiger-Mueller (GM) tube should be of a type that can also detect Alpha radiation, by virtue of incorporating a thin mica end window.

The larger in diameter of that thin mica end window, the more efficient, sensitive, and thorough will be the test.  These large ones are known as Pancake GM tubes, as in the Inspector line of instruments.

The Geiger counter should read out in a Digital display, preferred over an analog meter, for quantifying low levels of radiation that may be present.

The instrument should offer an automatic Timed Count or Timed Measurement feature that is necessary to reveal smaller levels of contamination that a momentary scan might miss.

Of the Geiger counter models within our selection that meet at least 1 of the above criteria, here is a comparison:  

Model/Criteria	Alpha	Pancake	Digital	Timed Count	Criteria Met
Monitor 4	Yes	No	No	No	1
Rad 100	Yes	No	Yes	Yes	3
Radalert 100X	Yes	No	Yes	Yes	3
Monitor 200	Yes	No	Yes	Yes	3
PRM-8000	Yes	No	Yes	Yes	3
Detector	Yes	Yes	No	No	2
Inspector Alert	Yes	Yes	Yes	Yes	4
Ranger	Yes	Yes	Yes	Yes	4
PRM-9000	Yes	Yes	Yes	Yes	4
Onyx	Yes	Yes	Yes	Yes	4
Frisker	Yes	Yes	Yes	No	3
Ranger EXP	Yes	Yes	Yes	Yes	4

Now for the specific details of checking for contamination, and here is my disclaimer - these are only procedures that I would follow and are not represented as the best or most thorough, or foolproof.  

Remove any packaging or housing that could otherwise shield radiation.

Always orient or aim any thin mica end window as close as possible to the substance without touching, so perhaps a quarter or half inch away.

When scanning liquids, pour into a shallow container of broad surface area.  Do not use a stone or metal container which could itself be weakly radioactive and distort the test - plastic or glass are probably best.  Likewise, do not set the container on a stone or granite countertop or floor.

Or in preparation for a scan of liquid, you could also absorb it with a paper towel, and then scan the moistened towel.

Start with a "momentary scan" by slowing moving the detector across the entire surface area, looking for any sustained increase in the radiation level beyond background, evidenced by a sustained increase in the frequency of any audible clicking, along with a sustained increase in the numerical level of radiation shown on any visual display.

If the momentary scan does not reveal any radiation from the substance, and if you want to be more thorough, then resort to a "timed count".  I recommend a sampling period of at least 10 minutes, and even longer depending on how thorough you choose to be.  The idea is that if a timed count of the substance, conducted for say 10 minutes, shows a higher accumulation of radiation than does a similar timed count of normal background radiation, then that test reveals a weak radiation emission that the momentary scan missed.

In the end, the effectiveness of a Geiger counter in detecting contaminated food and drink, in my opinion, comes down to a matter of degree.  Heavily contaminated food is potentially detectable by many Geiger Counters of reasonable sensitivity.  Weakly radioactive food might be detectable by some pancake GM tube models in combination with a timed count process.  But there could theoretically be a minimum amount of radiation particles missed by any Geiger counter.  So, anyone using a Geiger counter for this purpose needs to take responsibility for that decision, versus other alternatives.

As a matter of interest, I have scanned everything from milk to soy sauce to sake, and the only radioactive item I have found so far is a batch of captured Arizona rainwater.  Specifically, I detected 6 CPM (Counts per Minute) of radiation from the sample, using the Digilert 100 Digital Geiger counter, a standard-tubed (not pancake) model, so that instrument is still pretty sensitive to have achieved that feat.  I would add, though, that a momentary scan itself of the captured rainwater failed to reveal any contamination - the radioactivity become apparent only through a 20-minute timed count.

In another example, a Canadian customer used the Inspector to determine that his imported Japanese tea leaves were contaminated.  He conducted a 30-minute timed count, showing a total reading of 53 CPM from the tea, versus background alone of 35 CPM.   The difference of 18 CPM over a 30-minute period is not only statistically significant, but conclusively points to radioactivity from the food.

 

As an additional resource on the topic of detecting radiation in food, I repeat here a summary written by International Medcom, manufacturer of the Inspector Alert and Radalert 100 models of Geiger counter:

Accurate measurement of radiation in food requires a multi-channel analyzer and a special oven for ashing the food to concentrate the radioactivity. Our instruments have been used for experimental, educational, and screening purposes in checking food.

Measuring radiation in food is tricky. Naturally occurring radiation in potassium-rich food (such as bananas, when dried into banana chips, and salt substitutes) from Potassium 40 can easily be detected with the Inspector and (with less sensitivity) the Radalert 50. In the case of fallout from nuclear testing or accidents (such as Chernobyl), you would be looking mostly for Strontium 90, Cesium 137, and possibly Plutonium 239.  Of our instruments, the Inspector is the best for this application because of its higher sensitivity.  The Inspector’s efficiency for Sr90 and Cs137 beta is good, and it does detect the Cs137 gamma. It does detect Pu239, but Pu239 can have health effects at very low concentrations, which can be difficult to detect with any instrument.

Before you screen for radiation in food, you should establish a baseline measurement in the same location where you plan to test the food. It is best to accumulate the baseline counts for 12 hours as described below.

When you measure, you should put the mica window of the instrument directly over the food you are measuring, as close as possible. In the case of milk or other liquids, fill a container very close to the top so you can measure directly, without the glass in the way. If all your milk is from the same source, you might want to boil or evaporate some to concentrate it, then take a measurement from that. Set the display to Total and accumulate the counts for 12 hours in each location. Divide the total count for the period by the exact number of minutes to get the average CPM.

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