Radiation and Tea in Japan

[zeto]

I have a scintillation counter at my lab facility, and have used it myself.

Radioactivity is not terribly complicated, however the terms used and the actual effects are quite complicated. I will spoil the surprise ending here early... there is no standard conversion from beq to sievert...

First some definitions:

1bq = number of atoms required to reach 1 decay per second
1 sievert = 100 rem = joules of energy absorbed per 1 kg of mass

Now the horrible truth:
1 sievert = 0.01bq * radiation type factor * tissue factor * distance

The radiation type factor, radiation energy per emission, and tissue factor must be experimentally determined on a per radionuclide basis. Additionally, iodine is preferentially utilized by the thyroid, and radioactive iodine is most likely to affect that organ in lieu of others.

alpha = released helium
beta = released electron
neutron = neutron
x-ray = x-ray
gamma ray = gamma

Typical emissions from the reactors:
131I = beta
129te= beta
137Cs= beta
90Sr = beta

So typically alpha has a higher sievert conversion factor, and beta is safer... so there's that.

To further complicate matters, 1kg of total plant material has very little meaning, due to tissue uptake specificity. It's possible the leaves contain 90% of the radionuclides but the stems contain 50% of the mass... they then measure the radioactivity, pick the leaves and throw away 50% of the mass, nearly doubling the radioactivity. To even further complicate matters is brewing efficiency... maybe you only leech 50% of the radionuclides into the water, since they may intercalate cellular constituents that are not brewed into your drink... therefore you will not consume it.

The *most* valid way to determine how dangerous it is to drink tea, is to brew it, dehydrate it, then count the radioactivity by both radiation type (probably beta) and energy... then use that info to lookup conversion values to sieverts. To avoid this, since it's a ton of work, they just list a generalized limit on bq per kg material, because frankly people are lazy, it's expensive, and the technology to do this isn't really high throughput.

Here is a calculator that attempts to model these value conversions based on experimental tissue data on a per nuclide basis: http://www.radprocalculator.com/Gamma.aspx

[Catfur]

I am not going to post my lay calculations as I am likely making a mistake along the way.

PLEASE! However, hopefully we have somene trained in this realm to a degree who is willing to help us out? THANK YOU!

For any trained individuals, a simple question or questions would be ... based upn consumption over the period of 1 year (answered in millirems and sievert equivalent would be desirable):

Actual ingestion 1 kilo of 50 bq/kilo?
Drinking of tea from 1 kilo of 50 bq/kilo (I am assuming a less than 100% leach rate)?
Actual ingestion 1 kilo 250 bq/kilo?
Drinking of tea from 1 kilo of 250 bq/kilo (I am assuming a less than 100% leach rate)?
Actual ingestion of 500 bq/kilo?
Drinking of tea from 1 kilo of 500 bq/kilo (I am assuming a less than 100% leach rate)?

Is this then linear if we eat (or drink) 2 kilos, 3 kilos, etc?

Some facts to add to the discussion:

1) External vs. Internal - Most external sources of radiation are gamma/x-ray emission and cosmic rays (which behave like neutrons or beta particles but are often exotic forms of matter). Beta particles won't penetrate the skin very far and also won't penetrate the air for any long distance (many meters). Alpha particles are only generated by very heavy elements and you are rarely exposed to them except from radon (which is a major fraction of the radiation most people are exposed to). The primary element of concern is Caesium 137, which is a beta/gamma emitter. Because of the way beta/gamma is absorbed by the body, external vs. internal is pretty irrelevant (the gamma penetrates deeply, often going through without being absorbed, the absorbed betas behave very similarly to a gamma, in fact, an absorbed gamma will usually generate a beta). Caesium is distributed throughout the body, which treats it as potassium, so the dose is well distributed. Essentially, an internal caesium dose is the same as background radiation (absorbed alpha emitters such as plutonium, which is a bone seeker, and some of the beta emitters such as strontium (also a bone seeker) and iodine (a thyroid seeker) are different).

2) Calculating an absorbed dose - Caesium has a biological half life of 80 days (it is excreted in your urine like sodium and potassium), much shorter than the radiological half life of 30 some years. So using the biological half life is more appropriate than the radiological half life. So, with that out of the way. 1Bq = 1 decay per second. Decay energy (we will assume 100% of emitted gamma rays are absorbed, which is not true) of Cs-137 = 1.2 MeV (rounding up). So that's 1.2 MeV/s from one Bq. 1.2 MeV x 60 seconds in a minute x 60 minutes in an hour x 24 hours in a day x 160 days (total effective residence time of uptaken Cs in your body) = 16,588,800 MeV absorbed per Bq. Converting MeV to Joules you get 2.6 X 10^-6 Joules. Dividing by the average weight of a person (we'll say they are small) of 50 Kg that's 5.3X10^-8 Joules/Kg, or 53 nano Sieverts.

An acute, not chronic (which is less dangerous) of 100 REM (1 Sv) will cause an approximately 5% cancer increase. Using the linear-no-threshold model (known to be overly conservative), 100 mSv will generate a .5% increase in cancer, which is nearly statistical noise, since you're already about 33% likely to get cancer anyways. So, you need 2,000,000 Bq of Caesium to get 100mSv of absorbed radiation (being exceedingly conservative in our calculations). So, good luck getting there drinking 100 Bq/Kg tea.

[Chip]

Thank you, Zeto and Catfur, for your contributions to this important discussion.

It will take me a bit to digest ...

[GreenwoodStudio]

Awesome, way to make a guy feel really dumb, thanks Gonna go make stuff with dirt now...

[veritas caute]

I am not going to post my lay calculations as I am likely making a mistake along the way.

PLEASE! However, hopefully we have somene trained in this realm to a degree who is willing to help us out? THANK YOU!

For any trained individuals, a simple question or questions would be ... based upn consumption over the period of 1 year (answered in millirems and sievert equivalent would be desirable):

Actual ingestion 1 kilo of 50 bq/kilo?
Drinking of tea from 1 kilo of 50 bq/kilo (I am assuming a less than 100% leach rate)?
Actual ingestion 1 kilo 250 bq/kilo?
Drinking of tea from 1 kilo of 250 bq/kilo (I am assuming a less than 100% leach rate)?
Actual ingestion of 500 bq/kilo?
Drinking of tea from 1 kilo of 500 bq/kilo (I am assuming a less than 100% leach rate)?

Is this then linear if we eat (or drink) 2 kilos, 3 kilos, etc?

Some facts to add to the discussion:

1) External vs. Internal - Most external sources of radiation are gamma/x-ray emission and cosmic rays (which behave like neutrons or beta particles but are often exotic forms of matter). Beta particles won't penetrate the skin very far and also won't penetrate the air for any long distance (many meters). Alpha particles are only generated by very heavy elements and you are rarely exposed to them except from radon (which is a major fraction of the radiation most people are exposed to). The primary element of concern is Caesium 137, which is a beta/gamma emitter. Because of the way beta/gamma is absorbed by the body, external vs. internal is pretty irrelevant (the gamma penetrates deeply, often going through without being absorbed, the absorbed betas behave very similarly to a gamma, in fact, an absorbed gamma will usually generate a beta). Caesium is distributed throughout the body, which treats it as potassium, so the dose is well distributed. Essentially, an internal caesium dose is the same as background radiation (absorbed alpha emitters such as plutonium, which is a bone seeker, and some of the beta emitters such as strontium (also a bone seeker) and iodine (a thyroid seeker) are different).

2) Calculating an absorbed dose - Caesium has a biological half life of 80 days (it is excreted in your urine like sodium and potassium), much shorter than the radiological half life of 30 some years. So using the biological half life is more appropriate than the radiological half life. So, with that out of the way. 1Bq = 1 decay per second. Decay energy (we will assume 100% of emitted gamma rays are absorbed, which is not true) of Cs-137 = 1.2 MeV (rounding up). So that's 1.2 MeV/s from one Bq. 1.2 MeV x 60 seconds in a minute x 60 minutes in an hour x 24 hours in a day x 160 days (total effective residence time of uptaken Cs in your body) = 16,588,800 MeV absorbed per Bq. Converting MeV to Joules you get 2.6 X 10^-6 Joules. Dividing by the average weight of a person (we'll say they are small) of 50 Kg that's 5.3X10^-8 Joules/Kg, or 53 nano Sieverts.

An acute, not chronic (which is less dangerous) of 100 REM (1 Sv) will cause an approximately 5% cancer increase. Using the linear-no-threshold model (known to be overly conservative), 100 mSv will generate a .5% increase in cancer, which is nearly statistical noise, since you're already about 33% likely to get cancer anyways. So, you need 2,000,000 Bq of Caesium to get 100mSv of absorbed radiation (being exceedingly conservative in our calculations). So, good luck getting there drinking 100 Bq/Kg tea.

If cesium and strontium are treated like calcium and ossified how can its biological half life be 80 days? Ossified calcium has no such half-life... I'm not trying to argue I'm just interested (and a little confused). This is definitely not my field but once something is incorporated into bone I have trouble accepting the idea that it is excreted in 80 days. It would seem reasonable to assume that ossified radiological substances would become embedded and bombard local tissue continuously. I also don't trust the risk assessments with respect to cancer. But even if the risk were something in the nature of a thousandth of a percent increased lifetime risk that would be more than enough to warrant avoiding the stuff as far as I'm concerned. I should have the test results of those 3 teas by the end of the day. That lab took longer than expected...

[Devoted135]

I am not going to post my lay calculations as I am likely making a mistake along the way.

PLEASE! However, hopefully we have somene trained in this realm to a degree who is willing to help us out? THANK YOU!

For any trained individuals, a simple question or questions would be ... based upn consumption over the period of 1 year (answered in millirems and sievert equivalent would be desirable):

Actual ingestion 1 kilo of 50 bq/kilo?
Drinking of tea from 1 kilo of 50 bq/kilo (I am assuming a less than 100% leach rate)?
Actual ingestion 1 kilo 250 bq/kilo?
Drinking of tea from 1 kilo of 250 bq/kilo (I am assuming a less than 100% leach rate)?
Actual ingestion of 500 bq/kilo?
Drinking of tea from 1 kilo of 500 bq/kilo (I am assuming a less than 100% leach rate)?

Is this then linear if we eat (or drink) 2 kilos, 3 kilos, etc?

Some facts to add to the discussion:

1) External vs. Internal - Most external sources of radiation are gamma/x-ray emission and cosmic rays (which behave like neutrons or beta particles but are often exotic forms of matter). Beta particles won't penetrate the skin very far and also won't penetrate the air for any long distance (many meters). Alpha particles are only generated by very heavy elements and you are rarely exposed to them except from radon (which is a major fraction of the radiation most people are exposed to). The primary element of concern is Caesium 137, which is a beta/gamma emitter. Because of the way beta/gamma is absorbed by the body, external vs. internal is pretty irrelevant (the gamma penetrates deeply, often going through without being absorbed, the absorbed betas behave very similarly to a gamma, in fact, an absorbed gamma will usually generate a beta). Caesium is distributed throughout the body, which treats it as potassium, so the dose is well distributed. Essentially, an internal caesium dose is the same as background radiation (absorbed alpha emitters such as plutonium, which is a bone seeker, and some of the beta emitters such as strontium (also a bone seeker) and iodine (a thyroid seeker) are different).

2) Calculating an absorbed dose - Caesium has a biological half life of 80 days (it is excreted in your urine like sodium and potassium), much shorter than the radiological half life of 30 some years. So using the biological half life is more appropriate than the radiological half life. So, with that out of the way. 1Bq = 1 decay per second. Decay energy (we will assume 100% of emitted gamma rays are absorbed, which is not true) of Cs-137 = 1.2 MeV (rounding up). So that's 1.2 MeV/s from one Bq. 1.2 MeV x 60 seconds in a minute x 60 minutes in an hour x 24 hours in a day x 160 days (total effective residence time of uptaken Cs in your body) = 16,588,800 MeV absorbed per Bq. Converting MeV to Joules you get 2.6 X 10^-6 Joules. Dividing by the average weight of a person (we'll say they are small) of 50 Kg that's 5.3X10^-8 Joules/Kg, or 53 nano Sieverts.

An acute, not chronic (which is less dangerous) of 100 REM (1 Sv) will cause an approximately 5% cancer increase. Using the linear-no-threshold model (known to be overly conservative), 100 mSv will generate a .5% increase in cancer, which is nearly statistical noise, since you're already about 33% likely to get cancer anyways. So, you need 2,000,000 Bq of Caesium to get 100mSv of absorbed radiation (being exceedingly conservative in our calculations). So, good luck getting there drinking 100 Bq/Kg tea.

If cesium and strontium are treated like calcium and ossified how can its biological half life be 80 days? Ossified calcium has no such half-life... I'm not trying to argue I'm just interested (and a little confused). This is definitely not my field but once something is incorporated into bone I have trouble accepting the idea that it is excreted in 80 days. It would seem reasonable to assume that ossified radiological substances would become embedded and bombard local tissue continuously. I also don't trust the risk assessments with respect to cancer. But even if the risk were something in the nature of a thousandth of a percent increased lifetime risk that would be more than enough to warrant avoiding the stuff as far as I'm concerned. I should have the test results of those 3 teas by the end of the day. That lab took longer than expected...

Just to clarify, Catfur did not say that cesium and strontium are processed similarly to calcium. Rather, it is processed similarly to sodium and potassium, both of which are readily excreted.

[Chip]

I also don't trust the risk assessments with respect to cancer. But even if the risk were something in the nature of a thousandth of a percent increased lifetime risk that would be more than enough to warrant avoiding the stuff as far as I'm concerned. I should have the test results of those 3 teas by the end of the day. That lab took longer than expected...

Keep in mind, life is a constant risk. In the home, the second we walk out the door. The water we drink, the food we eat, and tea we drink whether from China, Japan, India. In fact, any international or domestic food poses different risk factors that potentially far exceed the radiation we are seeing. Driving, riding a bike, going for a walk or run, not going for a run or walk. Our diets contain too much sugar and fat ... the list is endless.

From what I am reading the risk factor is virtually nil in the real world application. There are so much greater risks that we take daily without thinking.

If we go around being scared of anything and everything, we will have nothing, no life worth living. But also to pinpoint this one small thing (so it seems) is perhaps obsessing about a small thing while overlooking far greater risks.

We must each decide how to live our lives, decide what risks to take and what risks to avoid.

As a forum we also must look closely at the facts and not draw distorted conclusions that can spread like ... well radiation. Therefore while we should respect the decision of an individual, we can disagree with it adamantly at the same time.

Regardless, we look forward to seeing the results from the lab and assessing those results. I have PMed my request to directly receive the resulting reports from the lab, do you need my email address?

[AdamMY]

Let me give you the following quote which I have no clue who said it first but it has constantly been backed up by medical science.

If you live long enough you will get cancer.

I am really not trying to make light of the situation, or cancer. I am just saying for something that everyone is bound to get in some way shape or form, the numbers given by catfur really are completely background noise.

It is like someone using the theory of relativity to claim someone should never stop moving during the day. All fitness implications aside, would the extra fraction of a second "gained" because time is moving "slower" for your body in motion, really make a noticeable difference in the length of your life as everyone gets old eventually?

(I am trying to remember, but in one of my physics classes we ran through a rough calculation, where if two identical people where born one at the north pole, and the other at the equator ( with some simplified assumptions about the earths rotation, i.e. the pole is fixed in terms of rotational motion), the difference between the "lengths" of their lives though a typical life time was only about half a second due to relativity).


*edit: fixed some typographical errors.

[Suutej_Tsaj]

Awesome, way to make a guy feel really dumb, thanks Gonna go make stuff with dirt now...

Same here. I tried to follow the explanations as closely as I could, but I've never been good in chemistry.
I just bought some Sencha and Gyokuro from a local teashop, after years devoted to Gunpowder. I had a couple of litres of the former, so hopefully it won't be enough to become a mutant. Still, as I drink mostly greens and whites, I look forward to buy more tea from Japan and I'd like to have more info about the current situation there. Perhaps the results will clarify it a bit.

[veritas caute]

Test results are in:

Sample 1 is O-Cha, supra
Sample 2 is Yuuki-Cha Sencha, supra
Sample 3 is Yuuki-Cha Gyokuro, supra

3 tea samples Received: 07-Jan-2013 Page 1 of 1
Results of Analysis
Sample Test Result Units Date Method
1 I-131 < 1 Bq/kg 11-Jan-2013 GAMMA
2 I-131 < 1 Bq/kg 12-Jan-2013 GAMMA
3 I-131 < 1 Bq/kg 11-Jan-2013 GAMMA

1 Cs-134 < 2 Bq/kg 11-Jan-2013 GAMMA
2 Cs-134 < 1 Bq/kg 12-Jan-2013 GAMMA
3 Cs-134 2 Bq/kg 11-Jan-2013 GAMMA

1 Cs-137 < 1 Bq/kg 11-Jan-2013 GAMMA
2 Cs-137 < 2 Bq/kg 12-Jan-2013 GAMMA
3 Cs-137 2 Bq/kg 11-Jan-2013 GAMMA

[Poohblah]

holy low readings batman. Looks like even the most paranoid would feel safe drinking those teas.

[veritas caute]

holy low readings batman. Looks like even the most paranoid would feel safe drinking those teas.

Yeah, even the lab tech said "the results were zero. there is no problem with the tea." ...this was when I was pressing him to release the results by phone. But I wanted the actual reading, which is posted.

So really what I take from this is:
1. All the teas are substantially free from contamination (1 or 2 bq can be found anywhere in the world).
2. the presence of c134 even though it's not at all harmful does indicated that the radiation from Fukushima did affect all of Japan. C134 could only have come from Diaichi. But this is a worldwide problem. At <10 bq/kq it's not something that should concern anyone.

I am still very happy I did the test and both O Cha and Yuuki-Cha have passed with flying colours. So I will be continuing to buy from them. Demonstrably safe sources.

[Chip]

That is tremendously great news! I have to admit after reading the news report, I was a bit concerned, but like most news reports there is a degree of selling the news involved which I suspected.

Thank you for posting them, but hopefully actual lab reports will be availalble for viewing by members who PMed a request?

If nothing else, it will be part of a continuing education since Fukishima.

Thank you again for taking the initiative and doing the testing.

[Catfur]

Just for the record, caesium is treated like sodium and potassium, and readily excreted from the body with a biological half life of ~80 days. Strontium is treated more like calcium, and some fraction of it will become ossified, I don't know what the biological half-life of strontium is. The bone seeking nature of strontium is why the radiological controls on strontium contamination are stricter than on caesium contamination. I haven't heard diddly about strontium contamination from Fukushima Daiichi.

[veritas caute]

For anyone who wants direct reports I will forward the ones I got to your e-mail and, of course, you can contact the lab directly to receive the actual reports. I provided the contact info above.

I am surprised by the low readings. Very pleasantly surprised.