BRAWM Question: testing food with Geiger counter

We have all seen blogs and demos of people testing various items such as food, rainwater, seaweed, etc with Geiger counters.

Question: If someone claims to have taken background samples of 38 CPM and tested food at 55 CPM, is that food safe?

I'm not an expert, but neither are most bloggers, but do you subtract test subject CPM from background CPM? (55 CPM minus 38 CPM to get 17 CPM in food sample). If so, would 17 CPM be safe or is any number above background unsafe?

At what level of CPM over background be cause for concern?

You see lots of stuff on the Internet and hear stuff from people. Thank you for your input.

Thusly Hath BRAWM Spake...

The bottom line is that if your Geiger counter reads above background on your food, it may be due to mischief by the Chinese, Russians, North Koreans, Iranians, al-Qaeda dirty underpants bombers, or possibly a banana in your pocket, but it absolutely, positively is NOT coming from Fukushima, whose radiation is harmless and undetectable except by the minions of Our Glorious Empire. Thusly hath BRAWM spake.

Professor Farnsworth

Nice straw man. To recap: 1.

Nice straw man.

To recap:
1. There are plenty of foods that are contaminated with fukushima fallout.
2. A geiger counter is too blunt an instrument to see it given that your food already has natural radiation in it. You need something like a germanium detector to separate those different sources of radiation.
3. Please feel free to buy your own germanium detector and do your own analysis. No need to depend on the minions of the empire. I would suggest this one so that you get good acceptance out at the potassium peak. http://www.canberra.com/products/485.asp
4. The fallout is not harmless but it is negligible compared to what is already there, at least on the west coast of the US.
5. I'm just a humble subatomic particle physicist, I'm not associated with BRAWM.

Yours, diemos.

Would you please comment on this?

Could "salt substitute" be getting more radioactive? See:
http://www.nuc.berkeley.edu/forum/218/potassium-chloride-getting-lots-mo...
Now, this poster may have asked the wrong question, because most of the answers assure him that KCl cannot be getting more radioactive. But the last response (mine, btw) suggests that Cs137 contamination might be the culprit. Seaweed/sea water is a source of KCl - but what if the source is accumulating Cs137 from Fukushima, which is then being concentrated along with the KCl? How would a diligent scientist prove/disprove this? How about a concerned shopper on a budget?

Professor Farnsworth

Anything could be

Anything could be contaminated.

"How would a diligent scientist prove/disprove this?"

Put it in a germanium detector and look for the gamma lines specific to each contaminant. Just like BRAWM does. Take a look at the data for this milk sample. http://www.nuc.berkeley.edu/UCBAirSampling/MilkSampling/2011-04-28. Notice the lines from natural K-40 and radon decay products. See the lines from the fukushima fallot. Notice that they let this sample sit in the detector and count gammas for 22 hours before they had enough data to conclusively say there was contamination.

This level of contamination would cause a geiger counter to give the same reading as an uncontaminated sample.

Mark said he put his KCl in the germanium detector and didn't see any fukushima fallout.

"How about a concerned shopper on a budget?"

They are SOL.

Diemos

A good channel and video to explain

You should take a second to watch this video example of your gieger counter can not measure in food.

Also check out the other videos on this channel for bionerd you will find some good examples of testing and such. I am not affiliated with this person or channel.

Enjoy.

http://www.youtube.com/watch?v=Silk2g8fS8Y&feature=plcp

It doesn't matter

It really doesn't matter what you read with your Geiger counter survey meter. The fact is that your Geiger counter isn't sensitive enough to detect contamination from Fukushima at the levels that BRAWM measured.

Besides, in order to detect Fukushima contamination, you need to do spectroscopy to identify the isotopes, and you can't do spectroscopy with a Geiger counter.

In order to detect Fukushima contamination, like BRAWM does, you need very expensive and sensitive Germanium detectors, as well as have the knowledge base of radioactivity that BRAWM has to interpret the results.

As explained below, the only thing your Geiger counter is showing you when you measure food and rainwater and whatever... is the natural radioactivity from Mother Nature that we are all exposed to.

Questions from the Peanut Gallery on your KCl test-

1. Did you try to find a pre-Fukushima sample of KCl for comparison?

2. Did you perform a chemical assay to verify the purity of the KCl you tested?

3. Where is the 5.5% alpha emission coming from if K40 is a beta/gamma emitter?

Professor Farnsworth

"3. Where is the 5.5% alpha

"3. Where is the 5.5% alpha emission coming from if K40 is a beta/gamma emitter?"

A sheet of paper will stop all alphas and a fraction of the betas. You cannot conclude from his measurements that there are any alpha emissions. The reduction in count rate could be from the reduced flux of betas.

Mark says "we can conclude radiation is not primarily alpha"

"Next I set about figuring out what kind of radiation was coming from the potassium chloride. The three kinds of radiation are shielded in different ways. If radiation is primarily alpha particles, a sheet of paper should stop them. So I tried it:"

"Piece of paper (0.1 mm) 94.4±2.1%"

"Since the radiation is not attenuated very much (94% passes through), we can conclude that the radiation is not primarily alpha particles."

I believe you should have directed your criticism to Mark, the experimenter. Allow me to direct my next question to both you and him:

4. Would either of you eat this stuff??

Professor Farnsworth

You gotta learn to read what

You gotta learn to read what scientists actually write and not what you think they write or what you would like for them to write.

The conclusion that "the radiation is not primarily alpha particles" is correct. The data indicates that the level of alpha radiation is somewhere between 0.0% to 5.6%.

Here's an example of scientific thinking:

IF - the radiation were primarily alpha particles
THEN - the reduction would be >50%
SINCE - the reduction in NOT >50%
THEN - the radiation is not primarily alpha particles.

One cannot draw any further conclusions about the level of alpha radiation without additional data.

"4. Would either of you eat this stuff??"

I would if my doctor told me to reduce my sodium. Otherwise I'd stick to salt. The radiation coming out is consistent with what I would expect given that I'm perfectly aware that K-40 is radioactive. I'm also aware that the body maintains a constant level of potassium so any excess potassium I eat will just be excreted away so no additional dose.

No need to invent any fukushima contamination to understand what the Geiger counter is seeing.

K-40 radiation

The person before you was correct — the 6% decrease is due to the attenuation of some of the low energy betas. I said that the source is "not primarily alpha particles," I did not say that it for sure included alpha particles. I was doing an elementary textbook experiment to demonstrate the effect of different materials on the radiation. If the attenuation had been nearly 100%, then I would have concluded that the radiation was primarily alpha particles (although a very low-energy beta emitter such as tritium would also have fit the description.) Of course, we knew beforehand that the radioactive isotope responsible for the emission is K-40, and I meant to show with some simple tests that the radiation fits K-40's nuclear decay data.

As for (1) and (2): potassium-40 is not produced in reactors. It was produced by nature billions of years ago and is still radioactive. I have tested this same sample with our germanium spectroscopic detectors and found the tell-tale 1460 keV gamma-ray line of K-40.

(4) Yes, I have eaten some of this KCl. But it tastes bad, so I generally do not eat it for that reason.

Mark [BRAWM Team Member]

Aren't you the least bit curious...

... If that 6% IS alpha radiation or not? And if it is alpha, from WHAT? If it were, oh, let's say, radium, would you still eat it?

Professor Farnsworth

Sure I'm the least bit

Sure I'm the least bit curious. Curiosity is the Achille's heel of all scientists.

But I don't have the time to subject everything I eat to a full analysis. If there was an actual reason to think there was contamination I might make the effort to do an analysis, but there's not.

Alpha emitters are a natural component of soil so they're in all the foods we eat at a low level. http://hps.org/publicinformation/ate/q1946.html

The question then becomes what level of contamination is enough that you would want to do something about it.

For myself, I'm going to go have some sushi tonight. I'll eat tuna and salmon and nori knowing full well that they are contaminated with cesium at levels that are unimportant compared to what I already receive. I'll eat it and enjoy it.

I truly am grateful that I have the technical background to evaluate these things for myself and can thus make informed decisions for myself. It must be terrible to live in constant fear surrounded by nuclear boogeymen in every shadow.

What IS your threshold for concern?

Your salt substitute test shows a reading over 10X background while a number of other tests posted on youtube show 2X. Radioactive tuna, radioactive kelp (kelp being a source of KCl), burning rocks... NOTHING seems to be a cause for concern, so you say. Why on Earth does BRAWN even exist? In case al-qaeda's #2 man constructs a "dirty underpants bomb", perhaps?

Professor Farnsworth

BRAWM exists because the

BRAWM exists because the Fukushima reactors had a meltdown and the scientists at Berkeley wanted to know how much fallout was reaching the west coast. I for one am grateful for the work that they did. In the days following the meltdown it was the only credible and timely source of info on the web about what was reaching the SF bay area. I was perfectly ready to bug out if the readings turned out to be high enough to be of concern. Luckily for the west coast it turned out to be a nothing burger.

"Your salt substitute test shows a reading over 10X background while a number of other tests posted on youtube show 2X."

Yup. The count rate is going to be proportional to the size of the sample. Double the amount of KCl and you'll get 20X background. Quadruple it and you'll get 40X background. We already know that count rate is proportional to the size of the sample. That's basic science.

"Radioactive tuna, radioactive kelp (kelp being a source of KCl), burning rocks... NOTHING seems to be a cause for concern, so you say."

Me? I'm concerned. I'm glad someone is measuring it so that I know how much to be concerned. I try to stay away from radionuclides as much as I can but there's always a cost/benefit ratio and I'm not going to incur enormous costs to avoid things that are not much of a threat.

As for burning rocks you should complain to the military that they should keep better track of their white phosphorous ammunition.

As for me personally I think nuclear power is a terrible idea. I just hate the idea of shivering in the dark more. Fossil fuels are eventually going to be used up. We have no plan B.

Yes we do, use the power from

Yes we do, use the power from the Sun.
California is bathed in sunlight,
think about it every time you turn on the Air Conditioning.
Solar energy will stop you from shivering in the dark, all you need to do for that is store the energy from the Sun,
and despite what the Nuclear industry desperately wants you to believe, this is not difficult to do.

Plan B is Solar power + energy storage.

Nuclear power is completely unnecessary.

Basic Science? - Now I've got you, Wernstrom!

"The count rate is going to be proportional to the size of the sample. Double the amount of KCl and you'll get 20X background. Quadruple it and you'll get 40X background. We already know that count rate is proportional to the size of the sample. That's basic science."

You might enjoy this clip - the guy packs over 20 lb of potassium salt on top of his Geiger counter, trying to break 100 cpm:
http://www.youtube.com/watch?v=9ug7LZY_8Ho

This seems to refute your claim, assuming we are referring to MEASURED count rate - the salt near the detector BLOCKS beta from the salt behind itself.

"I'm not going to incur enormous costs to avoid things that are not much of a threat."

The basic problem for humanity is that the nuke industry/govt plutonium junkies have defined cost vs threat for us all, with a little help from Price-Anderson.

"As for burning rocks you should complain to the military that they should keep better track of their white phosphorous ammunition."

Please consult a dictionary for the proper spelling of the element phosphorus. The adjective "phosphorous" means "glowing", and could be used, cleverly, to describe the appearance of plutonium, e.g.

I do appreciate your answer, and am trying to respond thoughtfully.

Professor Farnsworth

"I do appreciate your answer,

"I do appreciate your answer, and am trying to respond thoughtfully."

I do appreciate your desire to know, and am trying to guess the right balance between understandability and rigor in my answers.

Yes, you're right. To get the number exactly right you need to take into account self-shielding of the betas from the material. Only betas emitted in the surface layer will reach the detector. So the beta contribution will plateau after a couple of cm thickness in the sample.

I don't understand your point with the clip. He's got 20 cpm background and 550 cpm with his plastic bag sample.

Wha?? - Sorry, wrong clip!

Try this one:
http://www.youtube.com/watch?feature=endscreen&NR=1&v=XS2LHJ4ZRXM

In all seriousness, isn't a little more rigorous testing of salt substitutes warranted? Could they not be harboring an unanticipated concentration of Cs137, which their normal QC may not be looking for? Do you not acknowledge that HEPA filters in CA (see Enviroreporter in Santa Monica) have shown over 5X background late last year? I don't want to panic or cause same, nor avoid any food I normally enjoy - but if our govt "experts" won't even make unbiased data available to inform our decisions (due to their cost/benefit calculations), what's the point of having them? Assuming, of course, that "Government of the people, by the people, for the people" is not just an obsolete marketing slogan...

Professor Farnsworth

"In all seriousness, isn't a

"In all seriousness, isn't a little more rigorous testing of salt substitutes warranted?"

Why salt substitutes as opposed to anything else?

"Could they not be harboring an unanticipated concentration of Cs137"

Sure. but is there any reason to think that? Testing fish in the pacific is reasonable since a lot of cesium was dumped in the ocean. Testing rice from fukushima is reasonable because that is in the fallout path. Testing milk in california is reasonable since that's a bioaccumulation path. Why salt substitutes?

You can test anything but you don't have the resources to test everything.

"which their normal QC may not be looking for?"

I doubt that gamma spectroscopy is a part of anyone's QC.

"Do you not acknowledge that HEPA filters in CA (see Enviroreporter in Santa Monica) have shown over 5X background late last year?"

All the HEPA filter and rainwater measurements have been consistent with natural radon decay products. http://www.nuc.berkeley.edu/UCBAirSampling/measurement-of-radioactivity

I'm not sure what you want. The world's radioactive. All of your food is going to set off a geiger counter because all of your food has potassium in it. You have to have a level of contamination greater than what's already there from the potassium for a geiger counter to tell you anything.

Geiger counter measurements

Great question, thanks for asking.

Yes, one must always subtract a background measurement from the sample measurement to find the radioactivity of the sample alone. It is important that when making a background measurement that the setup remains exactly the same except that the sample is absent. Assuming this, it is correct to subtract the background rate of 38 counts per minute from the sample rate of 55 counts per minute to obtain the radioactivity from the source itself: 17 counts per minute.

Now does that mean the food is contaminated? What many people do not realize is that all foods are radioactive, so in general we expect there to be some counts above background. Foods contain potassium, which means they contain the primordial radioactive isotope 40K. Foods can also contain trace amounts of 226Ra and other 238U and 232Th decay products. A Geiger counter can detect the beta and gamma emissions from these isotopes.

To see how radioactive potassium is, please see my simple measurement of a canister of potassium chloride purchased at a grocery store — that canister comes in at 466 CPM above background. It is not radioactive because of Fukushima, and it is not unsafe.

You also mentioned people measuring rain and finding that it is radioactive. This is also completely natural. I wrote up a measurement of rainwater using a Geiger counter where I find significant radioactivity in the sample but it dies off with the characteristic time of the half-lives of radon decay products.

Geiger counters are rather blunt instruments; they can detect radioactivity but they cannot tell you which isotope is responsible for it. One might detect radioactivity using one of these instruments, but there is plenty of benign natural radiation out there (e.g., where does the 38 CPM of the background test come from?). A Geiger counter would really only be useful for finding contamination in northeast Japan and nowhere else in the world. To find any isotopes released by the Fukushima reactors one needs to use spectroscopic detectors, such as our germanium detectors. But what we have seen in our own measurements is that the amount of radioactivity from the Fukushima accident was very small here on the West Coast, and most traces have long since disappeared from our environment.

Mark [BRAWM Team Member]