Fukushima Fukushima radiation detection and measurement

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Use two GM tubes, only one with silver foil, one without, and measure the difference.

Use variant of above detector. If neutrons are all thermal, then no moderator is required. BF3 or He3 detectors are good choices. For high fluxes, maybe an ion-chamber enhanced with silver foil will work.

Bob S
I know some neutron detectors use two GM tubes with one having a neutron capturing foil and rely on the differential measurements as a form of neutron detection. I see they can be effective as merely a detector of neutrons - since the neutron activated foil will leave one GM tube with higher activity reading than the other (but even so not for continuous beams of unknown, possibly high, neutron/gamma fluxes).

However I am wondering as to their true effectiveness in a fluctuating high gamma and neutron radiation background since the gamma may saturate the signals of both GM tubes rendering differential readings ineffective? Also, unless they are in some kind of high density dual GM tube array, would such a detector (if they only have two GM tubes) not be very directionally dependent in their detection?

I thought most of the differential GM tube detectors with the activation foil tend to have a UHMWPE outer shell as neutron moderators to thermalize the neutrons first to improve effectiveness of activating the foil?
 
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I know some neutron detectors use two GM tubes with one having a neutron capturing foil and rely on the differential measurements as a form of neutron detection. I see they can be effective as merely a detector of neutrons - since the neutron activated foil will leave one GM tube with higher activity reading than the other (but even so not for continuous beams of unknown, possibly high, neutron/gamma fluxes).
Also works in continuous neutron fluxes.
However I am wondering as to their true effectiveness in a fluctuating high gamma and neutron radiation background since the gamma may saturate the signals of both GM tubes rendering differential readings ineffective? Also, unless they are in some kind of high density dual GM tube array, would such a detector (if they only have two GM tubes) not be very directionally dependent in their detection?
Not directionally dependent for neutrons and gammas from beta decay. In the circuit, the Geiger tube pulses are each converted to analog signals with a time constant of several seconds, and one signal is subtracted form the other. The Geiger tubes are very small, and work in high fluxes of neutrons and/or gammas.
I thought most of the differential GM tube detectors with the activation foil tend to have a UHMWPE outer shell as neutron moderators to thermalize the neutrons first to improve effectiveness of activating the foil?
See attached picture of "albatross" dual Geiger tube pulsed and continuous neutron flux detector (from 12/1970 CERN Courier) with 12.5 cm diameter polyethylene moderator.

Bob S
 

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Hi, Question
Could you tell me in layman terms what I would be looking for if I were testing Alaska seafood/produce. What would be the parameters for a hand held radiation detector? I want to purchase a detector, but want to get the right kind for the application. Will it display all types of radiation? Your help is much appreciated. Thank you. Chris
 
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Hi, Question
Could you tell me in layman terms what I would be looking for if I were testing Alaska seafood/produce. What would be the parameters for a hand held radiation detector? I want to purchase a detector, but want to get the right kind for the application. Will it display all types of radiation? Your help is much appreciated. Thank you. Chris
The limits for food are so low that a handheld detector does not really show much. It needs a lead chamber (to reduce background from floor and walls) and longer counting times to detect anything.
 
Also works in continuous neutron fluxes.Not directionally dependent for neutrons and gammas from beta decay. In the circuit, the Geiger tube pulses are each converted to analog signals with a time constant of several seconds, and one signal is subtracted form the other. The Geiger tubes are very small, and work in high fluxes of neutrons and/or gammas.
See attached picture of "albatross" dual Geiger tube pulsed and continuous neutron flux detector (from 12/1970 CERN Courier) with 12.5 cm diameter polyethylene moderator.

Bob S
I know it can work in a continuous neutron flux. I was getting at the idea that there should be a dose limitation at which point the efficiency of neutron capture by the film will decrease? Alternatively the GM tube reaches a saturation in signals. In both cases, what sort of dose are we talking about in a common neutron detector such as the dual GM tube construction ones you are talking about??

I mean by directionally dependent, as in if the GM detectors are cylindrical and axially parallel, and there is a highly collimated narrow beam of neutrons or gamma photons, then it is possible that say the gamma beam can irradiate on the foil covered GM tube leading to a reading while the non-foil GM tube shows no reading, leading to a false positive. This is purely hypothetical of course, and can easily be overcome by reducing GM tube size, and by using an array construction. In any case, this detection method is not error prone and works best for detection for neutron pulses with low gamma background for which one can definitively determine the difference in detection between the two GM tubes?
 
PietKulp--thanks-I will try to find a detector with these parameters. I want to get as many chefs testing as possible for a safe source of fish, thus putting pressure on the FDA, NOAA and the seafood orgs to come clean and get the processors to test each tender ship. Questions; 1)what would be the normal counting time? 2)Do all detectors test for all 3 radiation types coming from Fukushima? Thanks again, Chris
 
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PietKulp--thanks-I will try to find a detector with these parameters. I want to get as many chefs testing as possible for a safe source of fish, thus putting pressure on the FDA, NOAA and the seafood orgs to come clean and get the processors to test each tender ship. Questions; 1)what would be the normal counting time? 2)Do all detectors test for all 3 radiation types coming from Fukushima? Thanks again, Chris
I do not think that this is something chefs should do. The FDA does not need pressure, they will do it. American authorities will screen imported food from Japan. It is horribly expensive to buy the sensitive equipment that they have.

Counting times depend on how sensitive the detector is. Geiger-Muller tubes are not sensitive. One needs NaI (sodium iodide) scintillator crystals, the larger the better.

Such detectors are for gamma radiation, which will give a good idea of what radioactive isotopes are present, if you can measure the spectrum.

So this is expensive equipment. And still, I would not expect to it to be able to detect radiactivity in seafood. If you are worried, you can eat pre-March canned or frozen fish for a while.
 
PietKulp--thanks-I will try to find a detector with these parameters. I want to get as many chefs testing as possible for a safe source of fish, thus putting pressure on the FDA, NOAA and the seafood orgs to come clean and get the processors to test each tender ship. Questions; 1)what would be the normal counting time? 2)Do all detectors test for all 3 radiation types coming from Fukushima? Thanks again, Chris
Most handheld detectors rely on ionization to detect radiation, either gas ionization detectors (such as geiger muller tube detectors) or variants of solid state ionization detectors.

Depending on your choice of the detector it may not detect all three radiation types, e.g. some solid state diode detectors are primarily only sensitive to gamma photons. Furthermore, since the energetic particles released from radioactive decay or fission have different penetration depths through matter, such as through air, you have to bring the detector element close enough to the source in order to detect them (in particular, alpha and beta particles). Most detectors are designed and used for gamma detection. Alpha and beta detection will require special detectors used in a specific fashion, otherwise it will be ineffective.

In other words, if you are testing fish, your handheld detectors are probably good for detecting gamma rays, since they have long penetration depths (certainly enough to penetrate the fish). You may also be able to pick up beta decay with some detectors if you are close enough. But for alpha decay, you'd have to be _really_ close to the source which means if the fish ingested the source, and you are only scanning the outside of the fish from a good distance like most people are shown to be doing on TV, you wouldnt be able to pick it up.
 
PietKiup and Biscuitcheese--Thanks again. More info, more questions! Is the radiation from Fukushima gama photons? I would be testing directly on the fish. So if I'm interpreting this correctly, a solid state ionization detector is better than gas ionization.
Would the following be sufficient sensitivity:
1000 cpm/mR/hr or 108 pulses referenced to Cobalt-60 radiation of 1 µSv/h ambient
Alpha - from 4.0 MeV
Beta - from 0.2 MeV
Gamma - from 0.01 MeV
for radiation detection on a fish up close and personal? This unit is a halogen filled geiger muller?
 
I am a believer that in our free country people should not be denied the right to know. So if you are interested in knowing if your food/ingedients are 'radioactive' you should be allowed to have a way of checking it yourself also since food safety authorities ultimately only check by sampling.

However in general I think the health and safety considerations of food is ultimately best left to the federal health and safety authorities in your country.

Short of comparing to academic/government/commercial research labs, sometimes the health/safety authorities will even have better equipment and better knowledge on experimentation techniques than the average civilian. This can ensure you will not get a false negative or false positive results which can have conceivably bad consequences.

For example, I'd imagine a very due dilligent health and safety regulator can sample fish properly from a large batch and not only use proximity radiation detectors to detect for high levels of radioactive decay that will be evidence for contamination, but also process some food samples for mass spectrometry to detect trace concentrations of radioisotopes if they exist, such as alpha emitters that can otherwise escape detection, etc. No average civilian has mass spectrometers or photospectrometers (the best they can do is spend a few thousand on a radiation detector).

There are too many commercially available types of detectors to draw a generic answer. Different detectors will have different characteristics, so you need to choose the one best for your application. The detector you have is a conventional GM counter.

It will depend on the extent and nature of the actual contamination from this fukushima incident for which nobody really knows yet. However there are many exotic radioisotopes produced from fission, which your fish may or may not have ingested based on radioisotpes that may or may not have been released into the environment. Again nobody knows. Assuming the worst case (worst case being the fish is contaminated with all sorts of radioisotopes and still managed to survive capture into the food chain) then all three emitters need to be considered.
 
Thanks, Biscuitcheese. Yes, I too believe in a free country with a right to know and protect myself and my customers. So I will purchase a detector for testing the fish from the fishing grounds directly in the Kuroshio Japanese current. We only have one testing station in Alaska and that is Dutch Harbor, and it is random screening. My fish comes from the gulf area, where all the Copper River salmon pass thru. I have contacted my state health boards and they can't answer any of my concerns and said I should contact the FDA, who states that the fish are safe to consume, even though they aren't testing commerically caught fish yet. Don't really know how they came to the conclusion that the fish are safe. I'll be proactive, I'd rather spend a few bucks, test and know than develop cancer and wonder about if it was the fish. Peace.
 
I see on the news some restaurant owners (in japanese restaurants in asia and even a three michellin star chef in the states) have purchased radiation detectors as a guarentee of food safety (although while demonstrating on TV most hold their detectors so far away from the seafood that they are likely only going to detect gamma radiation only while alpha and beta emitters that are more toxic when ingested in general may not be detected in such a fashion). It seems to be better than doing nothing I suppose. Good luck I guess. Hopefully seafood contamination isnt bad. And here I was thinking the gulf oil issue was bad enough for the seafood here.
 
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PietKiup and Biscuitcheese--Thanks again. More info, more questions! Is the radiation from Fukushima gama photons? I would be testing directly on the fish. So if I'm interpreting this correctly, a solid state ionization detector is better than gas ionization.
Would the following be sufficient sensitivity:
1000 cpm/mR/hr or 108 pulses referenced to Cobalt-60 radiation of 1 µSv/h ambient
Alpha - from 4.0 MeV
Beta - from 0.2 MeV
Gamma - from 0.01 MeV
for radiation detection on a fish up close and personal? This unit is a halogen filled geiger muller?
So it is a gaseous detector, not very sensitive to gamma, most of which passes straight through it. It is not sensitive enough to screen for radioactivity at the levels that would ban foods. But it is affordable, and it might be a sensible business decision to buy one if customers are concerned.

... the FDA, who states that the fish are safe to consume, even though they aren't testing commerically caught fish yet. Don't really know how they came to the conclusion that the fish are safe. I'll be proactive, I'd rather spend a few bucks, test and know than develop cancer and wonder about if it was the fish. Peace.
Most likely, levels in Alaskan fish would still be below detection levels. Detection levels are really really low. Way below levels that a normal person would call unsafe.
 
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I found some data. Cs-137 in sardines is about 0.1 Bq/kg (wet weight). In 1986 (Chernobyl) it went up to almost 1 Bq/kg.

This is not a health risk. Levels in Swedish moose and reindeer are still elevated. An average of many samples was 100 Bq/kg. The EU limit for imported food is 600 Bq/kg. Fish from the sea won't come close to that.
 
I found some data. Cs-137 in sardines is about 0.1 Bq/kg (wet weight). In 1986 (Chernobyl) it went up to almost 1 Bq/kg.

This is not a health risk. Levels in Swedish moose and reindeer are still elevated. An average of many samples was 100 Bq/kg. The EU limit for imported food is 600 Bq/kg. Fish from the sea won't come close to that.
This depends where and also when the measurements are done on the food supply. The disaster is still ongoing, and they also recently purposely dumped large quantities of contaminated water into the ocean for which the real impact is truely unknown a priori.

Also, as mentioned, it is unlikely decay readings are effective since it is doubtful alpha decay is accounted for from such food screenings using radiation detectors. And even still, even with analytical techniques like mass spec, they are still only sampling food which maybe prone to errors. E.g. i am doubtful heath authorities consider the uneven contamination distribution due to bioaccumulation into their already limited statistical sampling.
 
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This is not a health risk. Levels in Swedish moose and reindeer are still elevated. An average of many samples was 100 Bq/kg. The EU limit for imported food is 600 Bq/kg. Fish from the sea won't come close to that.
In 2008/2009, wild boars shot at the german/czech border (in bavaria) showed an average CS-137 concentration of 7000 Bq/kg. That's way above the legal limit of 600 Bq/kg. Over 20 years after Chernobyl.

It's not fish, but it shows, for how long radioactive materials stay in the food chain.

http://www.spiegel.de/international/zeitgeist/0,1518,709345,00.html (english version)
 
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I think this question fits here best...

Since there are several estimates of released radioactivity, I would like to try converting "released radioactivity of isotope x" into "released mass of isotope x". I think this would help in imagining, how much of the reactor's inventory is gone.
But how do I do this?

My approach would be the following, but I'm not sure if it's right, if it's an okay estimate or if it's total ********. So please give me some feedback. ^^;

[...]

How much Cäsium-137 is there in Fukushima overall in all damaged reactors? (1-4)
You have the right basic idea, but you're missing a factor of log(2), I think.

Bq is the number of decays per second. So to get number of atoms that produces x decays per second, you take x Bq and divide by the decay constant (the probability of decay of 1 atom per second).

The Cs-137 half-life is 30.1 years, so the relation of half-life to decay constant is: lambda = ln(2)/tau ~ 0.693/30.17 years = 7.285 x 10^-10/s.

So 10 PB (that was released to the atmosphere) amounts to 1.373 x 10^25 atoms of Cs-137: mass of Cs-137 atom is 136.9 u x 1.660 x 10^-27 kg / u ~ 3.11 kg.

A guess at the total inventory of Cs-137 in cores 1-3 at Fukushima could be based on an ORNL study of the inventory of Cs-137 for a fully radiated core (Cs-137 takes a while to build up to an equilibrium value) at the Brown's ferry nuclear plant (a BWR like Fukushima with power rating of 1065 MWe: which gave 273 PBq, or 850 kg of Cs-137.

http://www.scribd.com/doc/51577387/MARK-I-Reactor-Meltdown-Analysis [Broken]

(see page 84 for the initial Cs-137 inventory).

Scaling this number by power ratios to the Fukushima cores 1-3, I get about 1600 kg of Cs-137, and another 630 kg or so from
core 4, which was in the spent fuel pool ... so ~ 2200 kg Cs-137 total might have been available for release. I'm not sure of the total content of the spent fuel pool at unit 4, though ...
 
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Kind of a challenge, Given radioactivity samples of example 4.0 Bq I-131 m^3, Cs-137 = 1.2 Bq/m^3 yielding a air dose rate of 5.5 micro Sv/hr http://www.mext.go.jp/component/english/__icsFiles/afieldfile/2011/05/02/1305673_050210.pdf [Broken] Hopefully this translated.
 
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NUCENG

Science Advisor
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You have the right basic idea, but you're missing a factor of log(2), I think.

Bq is the number of decays per second. So to get number of atoms that produces x decays per second, you take x Bq and divide by the decay constant (the probability of decay of 1 atom per second).

The Cs-137 half-life is 30.1 years, so the relation of half-life to decay constant is: lambda = ln(2)/tau ~ 0.693/30.17 years = 7.285 x 10^-10/s.

So 10 PB (that was released to the atmosphere) amounts to 1.373 x 10^25 atoms of Cs-137: mass of Cs-137 atom is 136.9 u x 1.660 x 10^-27 kg / u ~ 3.11 kg.

A guess at the total inventory of Cs-137 in cores 1-3 at Fukushima could be based on an ORNL study of the inventory of Cs-137 for a fully radiated core (Cs-137 takes a while to build up to an equilibrium value) at the Brown's ferry nuclear plant (a BWR like Fukushima with power rating of 1065 MWe: which gave 273 PBq, or 850 kg of Cs-137.

http://www.scribd.com/doc/51577387/MARK-I-Reactor-Meltdown-Analysis [Broken]

(see page 84 for the initial Cs-137 inventory).

Scaling this number by power ratios to the Fukushima cores 1-3, I get about 1600 kg of Cs-137, and another 630 kg or so from
core 4, which was in the spent fuel pool ... so ~ 2200 kg Cs-137 total might have been available for release. I'm not sure of the total content of the spent fuel pool at unit 4, though ...
I checked the initial loading in your reference against the method and information I provided in another thread. Your reference has about half the initial Cs-137 inventory but is within a couple percent on I-131.
 
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Kind of a challenge, Given radioactivity samples of example 4.0 Bq I-131 m^3, Cs-137 = 1.2 Bq/m^3 yielding a air dose rate of 5.5 micro Sv/hr http://www.mext.go.jp/component/english/__icsFiles/afieldfile/2011/05/02/1305673_050210.pdf [Broken] Hopefully this translated.
So I forgot to actually ask the question. These sample result levels released by mext don't jive with the radiation levels. Can any of you make sense of the radioactivity levels in japan vs the radiation levels. Earlier, I found a result listing that included samples, 1 cm rad and 1 meter rad, but I can't locate it now. Any help appreciated.
 
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swl

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I live in the Kanto area and I would like to be able to test the food I'm feeding my children, and the playgrounds and parks where they play.

It is my understanding that the Iodine 131 is now a non-issue so long as there is no further criticality of uncontained fuel. I also have the impression that the only serious concerns now are Cesium 134 and 137. Is this likely to be true?

If our 'only' worries are the two Cesium isotopes, then is it safe to conclude that I needn't be concerned about alpha radiation? If so, is it possible to measure the beta and gamma radiation from food using a GM tube or inexpensive scintillation meter?

Would GM meters or scintillation meters be useful for checking the ground and grass in the parks and schools where our children play?

The radiation levels at the nearest MEXT monitoring point indicates that the radiation in that area is only slightly above the historical background levels. Unfortunately, the nearest monitoring point is over 20 miles away, and it is my understanding that fallout can be distributed in a manner comparable to the spots on a leopard, or the stripes on zebra, so I think it would be good for our family, and the other families near us to have some information about our immediate area.

Thanks for reading.
 

Astronuc

Staff Emeritus
Science Advisor
18,547
1,682
I live in the Kanto area and I would like to be able to test the food I'm feeding my children, and the playgrounds and parks where they play.

It is my understanding that the Iodine 131 is now a non-issue so long as there is no further criticality of uncontained fuel. I also have the impression that the only serious concerns now are Cesium 134 and 137. Is this likely to be true?
Yes. It is expected that the noble gases Xe, Kr and volatiles I and Cs escaped from the plant and were transported in air. The Cs isotopes are the most persistent because of the longer half-lives.
See also this thread - https://www.physicsforums.com/showthread.php?t=500760

If our 'only' worries are the two Cesium isotopes, then is it safe to conclude that I needn't be concerned about alpha radiation? If so, is it possible to measure the beta and gamma radiation from food using a GM tube or inexpensive scintillation meter?
This information might help - http://hps.org/publicinformation/ate/q534.html [Broken]

Would GM meters or scintillation meters be useful for checking the ground and grass in the parks and schools where our children play?
Perhaps. It might be worthwhile to have an independent assay. Is there a local university which might monitor the local area?

The radiation levels at the nearest MEXT monitoring point indicates that the radiation in that area is only slightly above the historical background levels. Unfortunately, the nearest monitoring point is over 20 miles away, and it is my understanding that fallout can be distributed in a manner comparable to the spots on a leopard, or the stripes on zebra, so I think it would be good for our family, and the other families near us to have some information about our immediate area.

Thanks for reading.
The local deposition is likely to be variable as it depends on the release at the source and the variable meterological conditions following the release.
 
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I live in the Kanto area and I would like to be able to test the food I'm feeding my children, and the playgrounds and parks where they play.

It is my understanding that the Iodine 131 is now a non-issue so long as there is no further criticality of uncontained fuel. I also have the impression that the only serious concerns now are Cesium 134 and 137. Is this likely to be true?

If our 'only' worries are the two Cesium isotopes, then is it safe to conclude that I needn't be concerned about alpha radiation? If so, is it possible to measure the beta and gamma radiation from food using a GM tube or inexpensive scintillation meter?

Would GM meters or scintillation meters be useful for checking the ground and grass in the parks and schools where our children play?

The radiation levels at the nearest MEXT monitoring point indicates that the radiation in that area is only slightly above the historical background levels. Unfortunately, the nearest monitoring point is over 20 miles away, and it is my understanding that fallout can be distributed in a manner comparable to the spots on a leopard, or the stripes on zebra, so I think it would be good for our family, and the other families near us to have some information about our immediate area.

Thanks for reading.
I suggest a decent beta-gamma type meter. They are durable, easy to use and easy to find. You don't need to know alot to use them. they come with instructions. They won't give you the full picture on soil or food, but will give you an indication of good vs. bad. You can gain useful knowledge about the enviornment the kids are being exposed to.
 
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I am trying to understand the monitoring instrumentation and data generated. This forum is fascinating, but most of it way over my head.

Questions:

1. Is the federal government using instrumentation that is adequate or designed to provide the information regarding radiation fallout from Fukushima that is of value to the public?
If not, is anyone gathering appropriate data?
--what are the "best" instruments are being using?
--how are they calibrated?
--how often are they calibrated and under what circumstances would they require re-calibration?
--are the "limits" fixed or have they become a moving target?
--what is the story behind the failure of radiation monitoring equipment and the reduction in monitoring in view of an ongoing crisis?

2. In my experience with physiologic data, the increased automation of collection and analysis results in the lowering of expertise in the operator with a resultant decrease in the quality of the information obtained. Is it different in this type of monitoring?
 

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