Radiation monitoring at playgrounds in Fukushima

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guardia's picture
guardia
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Radiation monitoring at playgrounds in Fukushima

Here are files containing measured amounts of radiation for about a hundred school playgrounds in the prefecture of Fukushima per file:

http://www.pref.fukushima.jp/j/schoolmonita0405.pdf
http://www.pref.fukushima.jp/j/schoolmonita040602.pdf
http://www.pref.fukushima.jp/j/schoolmonita0407.pdf

As one can easily note, the radiation levels are consistently higher at 1 cm than at 1 m above ground. They are not taking samples to figure out what's actually in the dirt (anyone care to speculate?), but the question remains: Would you let your kids play there?

Samuel

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Probably....

Samuel -

Not being able to read Japanese all I could work with were the numbers.  I dropped several of them into the equation for calculating dose rates from a plane source assuming the measured levels were due to radioactive particulate released from the plants and were evenly distributed on the ground.

The dose rate from a plane source is calculated as follows:

1.  From on-contact to .1r, the dose rate is as measured on-contact.  (r = the radius of the plane source)

2.  From .1r to .7r, the dose rate = .333 x the on-contact dose rate

3.  Beyond .7r, the dose rate is caclulated using the point source equation (inverse square function)

I assumed the radius of the plane source to be 10 meters.  I also assumed the 1 cm dose rate measurements to be an on-contact reading (close enough for the calculation)  For an on-contact reading of 5.3 microSieverts/hr (taken from sample point 8 in your first link), the estimated dose rate at .1r, or 1 meter should be 5.3 microSieverts/hr.  It was measured at 3.2 microSieverts/hr.  Since the 1 meter dose rate was less, that tells me either the assumed radius was too large and it was less of a plane source and more a point source, or it was measuring background.

If you change the radius to 2 meters, the numbers should work out as follows:

From on contact to 20 cm (.1r), the dose rate is 5.3 microSieverts/hr

From 20 cm to 140 cm the dose rate would drop off to .333(5.3) = 1.77 microSieverts/hr

Again, since the dose rate measured at 1 meter was 3.2, nearly twice what it should be, that tells me that the readings are measuring very close to background levels since they don't change with distance as expected.  If you look at the other readings at other sample points, the 1 cm and 1 meter readings are even closer.

On pages 14 and 15 of the survey results in the first link provided, the readings at sample points 25, 26, 27 and 30 have readings significantly highers than on any of the other pages.  These values follow the plane source calculation - I would not let my kids play there.  I would encourage Harry Reid and John Boehner to play there.

What we would need to see are dose rate measurements taken before the accident to see what the normal background levels were.  Even then, using the numbers provided and the apparent fact that they don't fall off with distance as expected tells me that the measurements are background levels. 

Subject to isotopic analysis, given these numbers, with the above noted exception, I would let my kids play on the playground.

guardia's picture
guardia
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Re: Probably....

Dogs, thanks for looking into this!

(BTW, I made a mistake.. the whole three files actually contain results for about 1500 schools.)

The text isn't very important. It only indicates the name of the ward, school, and other obvious things like titles of the columns..

So, if I'm following you correctly, except for the few results with high readings, the rest are safe enough? What I am especially worried about are radionuclides that may be hidden in the dirt, in small enough quantities to not skew the results by much, but that could cause severe enough damage if inhaled, like plutonium (never know). Is it something that's plausible in your experience?

Thanks for the detailed analysis! Will come back a bit later to understand it better, and maybe with some additional questions :)

Samuel

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Fractals!

Ah ha, I think I have just figured out the info I was missing here.. As one can see from the contamination map of Chernobyl

radioactive particles tend to concentrate in some places and not others, somewhat randomly. It looks like Brownian noise to me, which is fractal in nature and also happens on a smaller scale, such that, on something like a playground, we would get planar or even point "hot spots" here and there. If radiation does not seem to follow a planar or point source model, it's probably background radiation of stuff that was already there before, that had time to spread around and get deeper in the earth.

But if we do end up with some point source plutonium here and there, even if it it measures just 2 uSv/h, it's not very reassuring I think... Let me search this up

Samuel

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DIAP,  If the radiation is

DIAP,  If the radiation is gammas coming from the dirt with effectively no shielding, then you have a plane source on the ground and you would expect no variation with height.  The only diminishing effect would be from the shielding effect of the air.  R=infinity.  The stuff is uniformly distributed everywhere.   

The main reason there would be a change in reading would be some shielding effect.  I suspect they are trying to find the contribution of the beta radiation.  Energetic betas could be detected near the source, but would be shielded by the meter of air.  Both Cs137 and I131 are beta emitters.

The worldwide average background dose for a human being is about 2.4 millisievert (mSv) per year.  => 0.3uSv/hr

I don't mind 2 to 5 times normal background - but 20 times or more is starting to get worrisome.  More to the point - is everybody living with this elevated background level and how much is 30yr Cs 137.  

 

 

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Guardia and Grondeau,   

Guardia and Grondeau,

    I found this paper insightful:

Comparing Japan's Radiation Release to "Background Radiation ...

 

Apologists for the type of old, unsafe nuclear reactors which are leaking in Japan argue that the amount of radiation released from Fukushima is small compared to the amount of "background radiation".

There Are NO Background Levels of Radioactive Caesium or Iodine

Wikipedia provides some details on the distribution of cesium-137 due to human activities:

Small amounts of caesium-134 and caesium-137 were released into the environment during nearly all nuclear weapon tests and some nuclear accidents, most notably the Chernobyl disaster. As of 2005, caesium-137 is the principal source of radiation in the zone of alienation around the Chernobyl nuclear power plant. Together with caesium-134, iodine-131, and strontium-90, caesium-137 was among the isotopes with greatest health impact distributed by the reactor explosion.

The mean contamination of caesium-137 in Germany following the Chernobyl disaster was 2000 to 4000 Bq/m2. This corresponds to a contamination of 1 mg/km2 of caesium-137, totaling about 500 grams deposited over all of Germany.Caesium-137 is unique in that it is totally anthropogenic. Unlike most other radioisotopes, caesium-137 is not produced from its non-radioactive isotope, but from uranium. It did not occur in nature before nuclear weapons testing began. By observing the characteristic gamma rays emitted by this isotope, it is possible to determine whether the contents of a given sealed container were made before or after the advent of atomic bomb explosions. This procedure has been used by researchers to check the authenticity of certain rare wines, most notably the purported "Jefferson bottles".

As the EPA notes:

Cesium-133 is the only naturally occurring isotope and is non-radioactive; all
other isotopes, including cesium-137, are produced by human activity.

So there was no "background radiation" for caesium-137 before above-ground nuclear testing and nuclear accidents such as Chernobyl.

Japan has already, according to some estimates, released 50% of the amount of caesium-137 released by Chernobyl, and many experts say that the Fukushima plants will keep on leaking for months. See this and this. The amount of radioactive fuel at Fukushima dwarfs Chernobyl.

Likewise, iodine-131 is not a naturally occurring isotope. As the Encyclopedia Britannica notes:

 

The only naturally occurring isotope of iodine is stable iodine-127. An exceptionally useful radioactive isotope is iodine-131...

 

And New Scientist reports that huge quantities of iodine-131 are being released in Japan:

Austrian researchers have used a worldwide network of radiation detectors – designed to spot clandestine nuclear bomb tests – to show that iodine-131 is being released at daily levels 73 per cent of those seen after the 1986 disaster.

(Indeed, some experts are saying that the amount of radioactivity released in Japan alreadyexceeds Chernobyl.)

Naturally-Occurring Radiation

There are, of course, naturally occurring radioactive materials.

But lumping all types of radiation together is misleading ... and is comparing apples to oranges.

As the National Research Council's Committee to Assess the Scientific Information for the Radiation Exposure Screening and Education Program explains:

 

Radioactivity generates radiation by emitting particles. Radioactive materials outside the the body are called external emitters, and radioactive materials located within the body are called internal emitters.

Internal emitters are much more dangerous than external emitters. Specifically, one is only exposed to radiation as long as he or she is near the external emitter.

For example, when you get an x-ray, an external emitter is turned on for an instant, and then switched back off.

But internal emitters steadily and continuously emit radiation for as long as the particle remains radioactive, or until the person dies - whichever occurs first. As such, they are much more dangerous.

Dr. Helen Caldicott and many other medical doctors and scientists have confirmed this. See this and this.

As Hirose Takashi notes:

All of the information media are at fault here I think. They are saying stupid things like, why, we are exposed to radiation all the time in our daily life, we get radiation from outer space. But that’s one millisievert per year. A year has 365 days, a day has 24 hours; multiply 365 by 24, you get 8760. Multiply the 400 millisieverts by that, you get 3,500,000 the normal dose. You call that safe? And what media have reported this? None. They compare it to a CT scan, which is over in an instant; that has nothing to do with it. The reason radioactivity can be measured is that radioactive material is escaping. What is dangerous is when that material enters your body and irradiates it from inside. These industry-mouthpiece scholars come on TV and what to they say? They say as you move away the radiation is reduced in inverse ratio to the square of the distance. I want to say the reverse. Internal irradiation happens when radioactive material is ingested into the body. What happens? Say there is a nuclear particle one meter away from you. You breathe it in, it sticks inside your body; the distance between you and it is now at the micron level. One meter is 1000 millimeters, one micron is one thousandth of a millimeter. That’s a thousand times a thousand: a thousand squared. That’s the real meaning of “inverse ratio of the square of the distance.” Radiation exposure is increased by a factor of a trillion. Inhaling even the tiniest particle, that’s the danger.

 [Interviewer] So making comparisons with X-rays and CT scans has no meaning. Because you can breathe in radioactive material.

 [Takashi] That’s right. When it enters your body, there’s no telling where it will go. The biggest danger is women, especially pregnant women, and little children. Now they’re talking about iodine and cesium, but that’s only part of it, they’re not using the proper detection instruments. What they call monitoring means only measuring the amount of radiation in the air. Their instruments don’t eat. What they measure has no connection with the amount of radioactive material. . . .

There are few natural high-dose internal emitters. Bananas, brazil nuts and some other foods contain radioactive potassium-40, but in extremely low doses.

As the American Journal of Public Health noted in 1962:

Of the radioisotopes originally present in rock-type formations, some may become internal emitters through natural processes. They may be leached or dissolved into ground and surface waters, thus gaining access to man's water and food supply. For either physical or biological reasons, only a few of the naturally radioactive heavy atoms are important sources of internal radiation exposure. The three most important are believed to be radium 226, the most abundant natural isotope of radium; lead 210, a daughter of radium 226 and of radon 222, and radium 228, a daughter of natural thorium.

 

Radon 222 has a half life of less than 4 days. Radium has a much longer half-life. However,radium ions do not form complexes easily, due to highly basic character of ions. Radium compounds are quite rare, occurring almost exclusively in uranium ores.

Some parts of the country are at higher risk of exposure to naturally-occurring radium than others. It is not only those built on top of uranium mines. For example, the American Journal of Public Health article notes:

 

Water derived from surface sources such as rivers, lakes, or wells penetrating unconsolidated sand or gravel deposits were, in general, found to contain considerably lower concentrations of radium 226 than wells penetrating deep sandstone formations of Cambrian or pre-Cambrian ages.

In contrast, cesium-137 - one of the main types of radioactivity being spewed by the Japanese plants - has a much longer half life, and can easily contaminate food and water supplies. As the New York Times noted recently:

 

 

Over the long term, the big threat to human health is cesium-137, which has a half-life of 30 years.

At that rate of disintegration, John Emsley wrote in “Nature’s Building Blocks” (Oxford, 2001), “it takes over 200 years to reduce it to 1 percent of its former level.”

It is cesium-137 that still contaminates much of the land in Ukraine around the Chernobyl reactor.

***

Cesium-137 mixes easily with water and is chemically similar to potassium. It thus mimics how potassium gets metabolized in the body and can enter through many foods, including milk.

As the EPA notes in a discussion entitled " What can I do to protect myself and my family from cesium-137?":

Cesium-137 that is dispersed in the environment, like that from atmospheric testing, is impossible to avoid.

Radioactive iodine can also become a potent internal emitter. As the Times notes:

Iodine-131 has a half-life of eight days and is quite dangerous to human health. If absorbed through contaminated food, especially milk and milk products, it will accumulate in the thyroid and cause cancer.

The bottom line is that there is some naturally-occurring background radiation, which can - at times - pose a health hazard (especially in parts of the country with high levels of radioactive radon or radium).

But cesium-137 and radioactive iodine - the two main radioactive substances being spewed by the leaking Japanese nuclear plants - are not naturally-occurring substances, and can become powerful internal emitters which can cause tremendous damage to the health of people who are unfortunate enough to breathe in even a particle of the substances, or ingest them in food or water. Unlike low-levels of radioactive potassium found in bananas - which our bodies have adapted to over many years - cesium-137 and iodine 131 are brand new, extremely dangerous substances.

And unlike naturally-occurring internal emitters like radon and radium - whose distribution is largely concentrated in certain areas of the country - radioactive cesium and iodine are spreading not only nationally, but world-wide.

At the very least, it is important to note that each individual internal emitters behaves differently. They each accumulate in different places in the body, target different organs, mimic different vitamins and minerals, and are excreted differently (or not at all). Therefore, comparing radioactive cesium or iodine with naturally occurring radioactive substances - even those which can become internal emitters - is incorrect and misleading.

This is not to say that we're all going to get cancer. Most of use probably won't. This is solely an attempt to counter the misleading propaganda from apologists for old, unsafe nuclear reactors. For background information on "safe" radiation levels, see this.

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Xray,  certainly beta

Xray,  certainly beta emmitters are more problematic once ingested - and indeed most background radiation is gammas.   I would argue that once you specify the nature of the radiation - alpha, beta, or gamma - and to a lesser extent the energies, you can treat the biological effects of the various isotopic emmiters the same.  For example, I131 decays with a 0.6Mev beta, and Cs137 with a 0.51MeV  beta 90% of the time and a 1.2MeV beta 6% of the time.  Those energetic betas will collide with surrounding particles and slow down and stop over a distance of several millimeters in tissue, breaking chemical bonds and generating ions in the process.  Most beta emmiters that you will pick up with a gieger counter will have energys of several hundred keV or higher and few isotopes have betas with energies greater than 3MeV, so a count is a count - to within a factor of ten! 

Alphas are the worst for doing damage when ingested.  they deposit all of their energy in a very short range.  This means you get severe disruption of local cells with a single disintegration.  Their geiger counters will not pick up any alphas because they would be stopped in the detection windows of the geiger tubes.  I would guess the worst alpha sources would be plutionium and uranium.  Fortunately, I don't think there is much of that out yet.

So, the real issue for japan is how much beta emmiters are tolerable?  Hence the need to test food and worry about dust on a playground.  Presumably, cleaning up the playgrounds by either vaccuming up the dust or encapulating it under a few inches of dirt could diminish the problem.  You would still have the gammas, but as you point out - the betas are worse.

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Need more data

Thanks guys for all the input! I guess we will just have to wait for more data about what exactly has fallen where, and to sit tight in the meantime... Or maybe they are being cynical about all this thinking something along these lines: "We'll probably get a couple more explosions in the next few months and may need to redo the readings anyway, so let's try to wait this out the longest possible" ... Yell

Samuel

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The nightmare: airborne uranium and plutonium

First evidence of global contamination from alpha-emitting particulates from
Fukushima. Elevated Uranium in air filters in Hawaii and Marianas islands

Quote:

Clearly the levels in the Pacific air samplers are much higher that the levels
found in the AWE filters even at the time of the Gulf War.
If we assume that the background level in the Pacific is around 300nBq/m3 then
the detection of between 4000 and 10,000nBq/m3 represents a very significant
and alarming increase in Uranium concentration and suggests (a) that further
measurements of uranium particulates should be carried out globally and (b)
that the levels of particulates in Japan and nearby countries within 2000km
radius may be dangerous.

I'm living a nightmare... Can anyone comment on this? thanks

Samuel

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Japan Held Nuclear Data, Leaving Evacuees in Peril

 http://www.nytimes.com/2011/08/09/world/asia/09japan.html?_r=1

FUKUSHIMA, Japan — The day after a giant tsunami set off the continuing disaster at the Fukushima Daiichi nuclear plant, thousands of residents at the nearby town of Namie gathered to evacuate.

Given no guidance from Tokyo, town officials led the residents north, believing that winter winds would be blowing south and carrying away any radioactive emissions. For three nights, while hydrogen explosions at four of the reactors spewed radiation into the air, they stayed in a district called Tsushima where the children played outside and some parents used water from a mountain stream to prepare rice.

The winds, in fact, had been blowing directly toward Tsushima — and town officials would learn two months later that a government computer system designed to predict the spread of radioactive releases had been showing just that.

But the forecasts were left unpublicized by bureaucrats in Tokyo, operating in a culture that sought to avoid responsibility and, above all, criticism. Japan’s political leaders at first did not know about the system and later played down the data, apparently fearful of having to significantly enlarge the evacuation zone — and acknowledge the accident’s severity.

Hmm...what else haven't they admitted to yet?

 

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Just a guess....
jumblies wrote:

 http://www.nytimes.com/2011/08/09/world/asia/09japan.html?_r=1

FUKUSHIMA, Japan — The day after a giant tsunami set off the continuing disaster at the Fukushima Daiichi nuclear plant, thousands of residents at the nearby town of Namie gathered to evacuate.

Given no guidance from Tokyo, town officials led the residents north, believing that winter winds would be blowing south and carrying away any radioactive emissions. For three nights, while hydrogen explosions at four of the reactors spewed radiation into the air, they stayed in a district called Tsushima where the children played outside and some parents used water from a mountain stream to prepare rice.

The winds, in fact, had been blowing directly toward Tsushima — and town officials would learn two months later that a government computer system designed to predict the spread of radioactive releases had been showing just that.

But the forecasts were left unpublicized by bureaucrats in Tokyo, operating in a culture that sought to avoid responsibility and, above all, criticism. Japan’s political leaders at first did not know about the system and later played down the data, apparently fearful of having to significantly enlarge the evacuation zone — and acknowledge the accident’s severity.

Hmm...what else haven't they admitted to yet?

 

We will probably find more such instances - with the luxury of hindsight.

That is why they are called lessons learned.

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Dogs_In_A_Pile wrote: We
Dogs_In_A_Pile wrote:

We will probably find more such instances - with the luxury of hindsight.

That is why they are called lessons learned.

I suspect they're more like just lessons. I don't see a great deal of learning happening, sadly.

 

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