Debunked: High Radiation Readings in Japanese Green Tea, linked to Fukushima?

Balance

Senior Member.
[Admin UPDATE Jan-18-2014]

Yuuki-Cha tea has posted certificates on their web site, which they say show all teas tested are below detectable limits of radioactive cesium and iodine. I have no reason to doubt this. I think that the teas are all perfectly safe, and the video below is irresponsible scaremongering.

http://www.yuuki-cha.com/test-results (http://archive.is/WnnZ9)

While I have no reason to doubt the levels, it is unfortunate that the certificates are not readable.

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[Admin UPDATE: Jan-12-2014]
The videoed test is useless and misleading. Calculated using the figures in the video, the tea has about 30 Bq/Kg. By comparison a banana naturally has 130 Bq/Kq. The legal limit for tea leaves is 500 Bq/Kg. However there are really too many variable to make an accurate determination. What is missing from the video is a test of the measuring setup against a reference material, such as a banana]

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Original post follows:

I've just been alerted to this video, could someone please decipher what it's really showing. From previous radiation debunks, I guess it's a flawed test and even if not, those readings are not a problem? Thank you.


 
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Balance

Senior Member.
If I knew what I was looking at, maybe. But this is probably so wrong. He carries out a number or svrts/hr counts (100mins each) of no tea, tea and tea blocked by various materials, aluminium, paper, wood etc. The no tea averages 4000+ while the other tests show elevations of another 1000+ counts. If you skip to 8:30 there's a table of data.
 

Mick West

Administrator
Staff member
If I knew what I was looking at, maybe. But this is probably so wrong. He carries out a number or svrts/hr counts (100mins each) of no tea, tea and tea blocked by various materials, aluminium, paper, wood etc. The no tea averages 4000+ while the other tests show elevations of another 1000+ counts. If you skip to 8:30 there's a table of data.

I've attached the table to your OP.

sverts/hr is a different reading from CPM. Attached here is the manual for the meter:


Geiger counters can detect the four main types of ionizing radiation: alpha, beta, gamma, and x-rays. Some detect only gamma and x-rays. Our instruments are calibrated to Cesium 137, but also serve as excellent indicators for many other sources of ionizing radiation. Gamma and x-rays are measured in milliroentgens per hour (mR/hr), microsieverts (μSv/hr), or millisieverts (mSv/hr). Alpha and beta are measured in counts per minute (CPM) or counts per second (CPS).

The window of the GM tube is very thin mica. This mica window is protected by a screen. Some levels of alpha, low energy beta, gamma, and x-rays that cannot penetrate the plastic case or the side of the tube can be sensed through the window.

Try not to touch the instrument to any suspected radioactive substance.

Although some beta and most gamma radiation can go through protective gear, try to avoid skin contamination and ingestion. When you leave a radioactive area, remove any protective outerwear and dispose of it properly. If you think you have been contaminated, as an additional precaution, shower and consult a physician.

How to Determine Alpha, Beta, or Gamma source.

To determine whether the radiation detected is alpha, beta, or gamma, hold the instrument toward the source.

Alpha: If there is no indication through the back of the case (the side of the tube), position the window close to but not touching the source. If there is an indication, it is alpha, beta, or low energy gamma. If a sheet of paper placed between the window and the source stops the indication, it is most likely alpha. To avoid particles falling into the instrument, do not hold the source above the window.

Beta: Place a piece of aluminum about 1/8 inch (3 mm) thick between the instrument and the source. If the indication stops, decreases, or changes, it is most likely beta radiation. Most common isotopes emit both beta and gamma radiation. This is why the indication would decrease or change but not stop.

The non-occupational dose limits set by the government is 100 mR above background annually.

It is up to the individual to decide what a safe radiation level is. It will be different depending on the individual and their knowledge of radiation and its affects. Radiation levels will vary according to location and circumstances. As an example; if your background level is 25 CPM (counts per minute) where you live, when you fly in an airplane at 30,000 feet your rate meter may measure 200 CPM (.2 mR) for 2 to 5 hours. That is 8 times your normal background radiation on the ground, but it is only for a limited amount of time.

When measuring radiation in an emergency response situation, it is good to have something to compare your readings to. Taking a background radiation level reading in your area before a radiation event will help you determine if you have an elevated level of radiation and whether or not to stay in that location. Background radiation is naturally occurring radiation that is always present. It includes high energy gamma rays from the sun and outer space and alpha, beta, gamma radiation emitted from elements in the earth. Using a rate meter, you can determine your normal background radiation levels.

Content from External Source
 

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Mick West

Administrator
Staff member
The issue seems to be real, the question here is if these readings actually mean anything.
http://edition.cnn.com/2011/WORLD/asiapcf/06/17/japan.green.tea/

CNN) -- Japan's green tea fields sway in the early summer winds, the picture of bucolic beauty. But beneath these peaceful rows of young green buds, ready for the second harvest of the year, a national crisis is brewing.

Earlier this month, Japan's government banned green tea from parts of three prefectures: Tochigi, Chiba and Kanagawa; and banned tea from all of a fourth prefecture, Ibaraki.

The authorities had detected levels of radioactive cesium in tea leaves above the legal limit of 500 becquerels per kilogram.

Now the discovery of radiation in fields further south in Shizuoka, Japan, some 400 kilometers away from the crippled Fukushima Daiichi Nuclear Plant, threatens the most robust tea-producing region in Japan.

The Shizuoka government says it asked five tea manufacturing plants in the Warashina district of Shizuoka to voluntarily stop shipping green tea leaves, after tests revealed dried tea contained 581 to 654 becquerels of cesium per kilogram.
Content from External Source
 

Balance

Senior Member.
Yes, my non-understanding is the different types of radiation. This article focuses on cesium and uses a metric of Bq/kg

http://www.teamuse.com/article_110701.html


So Is It Safe Or Not?

Yes, most of Japan’s tea is safe. Tea from the Uji region, and the Yame, Kumamoto, Miyazaki and Kagoshima prefectures have not been found to have any radiation to date; they are all west of areas where radiation has been found. There technically is detectable cesium in all Shizuoka’s tea, though it seems that most does not exceed government standards. The jury is still out on how much of Shizuoka’s teas have been affected and whether it is localized to certain areas of the prefecture or certain processors. For what it’s worth, the acceptable radiation levels being used by the Japanese government are far more stringent than both United States and WHO standards, which can only benefit tea consumers. Obviously, pregnant women and children need to be extra cautious about radiation exposure in general. We should all consistently make informed decisions about what we put in our bodies – not just tea.
Content from External Source
 

Mick West

Administrator
Staff member
From the manual:

Becquerel (Bq) is defined as the activity of a quantity of radioactive material in which one nucleus decays per second. 1 dps (one disintegration per second).
Content from External Source
A nucleus decay makes the geiger counter click. So if it counts every decay and you have 1Kg of a substance containing 1Bq, you will get 1 count per second, 60 CPM, a tick--tick--tick on the geiger counter. If it has 500 Bq/Kg, you would get 500 counts per second, 30,000 CPM, a high pitched buzz on the counter.

However not all disintegrations are measured, so counts per minute is actually a fraction of the disintegration per minute, the detection efficiency, which this meter has labeled as 25%

Energy Sensitivity
Detects Alpha down to 2 MeV. Detects Beta down to .16 MeV; typical detection efficiency at 1 MeV is approx. 25%. Detects Gamma down to 10 KeV through the end window. 3340 CPM/mR/hr (Cs137). Smallest detectable level for I125 is .02 μCi at contact.
Content from External Source
The bag has 50g of tea.



The number he keeps saying "average of data points" is just the average counts per second. It's the same as CPM/60, so it's pointless having both there. But you can take that CPS number, and note that to measure the amount in a substance, you actually need to subtract the background, adjust for sensitivity, and adjust for the mass of the sample, so:

(Measured rate - Background rate)/(Sensitivity %)*1000/(weight in g) = Bq/Kg
(0.84-0.47)/0.25*1000/50 = 29.6 Bq/Kg

By comparison, bananas naturally have around 130 Bq/Kg.

And this is well below the legal limit of 500, hence the tea is safe.

(Science check appreciated, @FireOfficer1822 )

(Explanation of Math)
(0.84-0.47) is the measured rate, minus the background rate. So this is the additional radiation being put out by the tea.
/0.25 is the correction for the 25% sensitivity. It's like multiplying by 4. It converts from CPS to DPS (Counts per second to decays per second)
*1000/50 converts from per 50g to per 1Kg (1000g)
 
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Balance

Senior Member.
That's assuming he's measuring the whole 50g, which it does look like. Would like to read FireOfficer's take on this too.
 

Mick West

Administrator
Staff member
I'm thinking I might need to also account for geometry here. The decaying particles are emitted in a random direction, so are only detected if they hit the sensor, so would depend on the size of the sample, and the position and size of the detector.

I can't immediately see how to figure this out though.
 

Mick West

Administrator
Staff member
But, the manual says:

Internal Halogen-quenched, uncompensated GM tube with thin mica window, 1.4-2.0 mg/cm2 areal density. Effective diameter of window is 45 mm (1.77 in.). Radiation symbol on front label and end panel marks the center of the detector.
Content from External Source
I'm assuming it's this radiation symobol (small, in the middle)


Looks like about a 40mm distance to the detector - quite close over the tea. So here:

a = 45/2 = 22.5
r = h + 40
...
[To be finished.... dinner time]
 
Thank you for the Tag Mick. Whle the math is correct it is also somewhat misleading (not do to anything on your part.) The conversion used is based on Cs137 and does differ slightly when discussing other isotopes. The later statement made by Mick:

I'm thinking I might need to also account for geometry here. The decaying particles are emitted in a random direction, so are only detected if they hit the sensor, so would depend on the size of the sample, and the position and size of the detector
.

is mostly correct. Accounting for the variables in detection range and surface area of instrumentation does increase the accuracy of the estimate but still does not give a "true" total. You also have to account for the background levels. The only way to get a "true" reading is going to be in the lab.



I love it when people mention the banana because lo and behold there IS a technical phrase used in radiological science to cover this. It is called the BED or Banana Equivalent Dose ! The BED is 9.82×10−8 sieverts or for those that hate exponents .1 microsieverts. A 150g Banana is equal to about 15 Bq.



A Point to remember when measuring radiation is you have to understand that alpha/beta and gamma radiation travel in 2 distict fashions. Alpha/Beta radiation is Particle based where Gamma Radiation is Wave Based. The CPM measurement is a good indicator for particles as there is a standard of travel i.e. Particles are going to tend to travel together in a semi sync'd fashion. Gamma Waves on the other hand to predict their flow we have to take a quick look at fluid dynamics and interference . Warning Science content ! There are 2 types of interference constructive and destructive. In constructive interference 2 waves are in phase (the peaks and troughs line up) the magnitude of the wave is increased. In deconstructive interference the 2 waves are out of phase and cancel each other out. This is why CPM is used primarily for Alpha/Beta measurements only becuase in the field there is simply no way to account for the expression of interference in counting the propagation of Gamma waves so we typicaly concern ourself with the dose rate. As I have said before about CPM since Alpha and Beta Radiation pose no external risk as non scientists our concern should be with dose rate anyway. unless writing a paper (or debunking on Metabunk) which is more important the actual count of decay propagation or the measure of risk to you ?

Image shows how 2 point sources interact.
 

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Chew

Senior Member.
The doomsdayers have been attacking the BED lately. They quote some guy who says potassium is homeostatically controlled so the level of potassium never changes so you just excrete out the excess potassium. Which is baloney. Potassium is used by our bodies and has to be replenished. The RDA is 4.7 grams. When I point this out to the people who obviously got this bit of wisdom from the fearmonger sites I tell them another way to think about it is our RDA of potassium is 145 Bq. There just isn't any way to avoid it. K-40 is in everything we eat.
 

Mick West

Administrator
Staff member
Really what the maker of this video should do is compare a packet to tea to a sliced banana, using the exact same setup and positioning. Since the banana is a semi-known and easily-obtainable reference, it will tell you if the radiation is higher or lower than a banana.
 

az09

New Member
So is the tea safe to consume? im really confused with all kinds of testings and theories going around. If the vendor did the test and it showed clear from radiation than why is person doing test in youtube video found radioactivitiy? can some one please explain that to me and i consume matcha everyday
 

Mick West

Administrator
Staff member
So is the tea safe to consume? im really confused with all kinds of testings and theories going around. If the vendor did the test and it showed clear from radiation than why is person doing test in youtube video found radioactivitiy? can some one please explain that to me and i consume matcha everyday

This is an old story. There was never anything scientific to suggest that there was any problem with the tea. And even if there was it would be irrelevant data now.
 

az09

New Member
This is an old story. There was never anything scientific to suggest that there was any problem with the tea. And even if there was it would be irrelevant data now.
i know its an old thread but as a regular consumer i want to know why would be the tea be radioactive from scientific point of view if the tests from vendor show no cesium. Is it radioactive because of naturally occuring isotopes from soil?
 

Mick West

Administrator
Staff member
i know its an old thread but as a regular consumer i want to know why would be the tea be radioactive from scientific point of view if the tests from vendor show no cesium. Is it radioactive because of naturally occuring isotopes from soil?

Everything is radioactive to some degree, bananas being a classic example. In this case it just seems like the measurement technique was not very good. You need more specialized equipment to get an accurate measurement, as discussed in the thread above.
 

Redwood

Active Member
The main radiation danger would have been Iodine-131, which is readily absorbed into the body. However, its half life is only 8 days so all that was produced in Fukushima is now gone. The radioactive decay product of Iodine-131 is non-radioactive Xenon-131.
 
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