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:

 

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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/
 

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

 

Mick West

Administrator
Staff member
From the manual:
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%
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:
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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