[Column] What is Sv, Bq, Cesium, how and why it matters

I’m often asked what is Bq/Kg and what is Sv/h etc.. I’d like to explain it in the most casual way in the world.

For example, if I shout from the window, my neighbors are annoyed. My voice to be heard by my neighbor is Sv. Sv = 1000 mSv = 1,000,000 μSv.
and if you put your ear directly on my mouth, that would be louder. This is Bq.
How much you are annoyed is Sv, how noisy I am is Bq.
so even if I’m 10000000000 Bq/Kg, if you are so far from me, you don’t hear me (0Sv). On the other hand, even if I’m just 1 Bq/Kg, if you are 1cm away from me, you’d be so annoyed (100Sv or something).
This is why you cannot use a geiger counter to know how much food is contaminated. It would only show how much radiation the geiger counter caught emit by the food. As it flies, radiation is weaken. To know how much it’s contaminated, you need to take it to a lab and analyse. The result is in Bq/Kg.

They say you wouldn’t die even if you are exposed to 2 Sv or something, so even if you detect 0.20 μSv/h, it’s nothing. The trick is where the radiation is from. After 311, Japan was covered with radioactive dust. If you detect 0.20 μSv/h in Tokyo, it’s likely to be from the dust on the ground. Because radiation gets weaken as it flies, you may detect 20 μSv/h or something if you put your geiger counter directly on the dust. The problem is that you may breathe it into your lungs.
It’s like swallowing the burning coal. Even if you get close or touch the burning coal for a moment, it’s nothing, but if you swallow it, that’s another story. “You don’t die of 2 Sv” means you don’t die even if you are close to the burning coal. so basically, you can use your geiger counter only to know if there is radioactive dust around you or if a nuclear reactor is exploding at this moment.
Due to the sort of ground or sunshine, you detect 0.2 ~ 0.3 μSv/h (Higher than current Tokyo) in some places in the world, but you don’t swallow sunshine and you don’t eat the radiation ray from the ground. It’s just like the warmth of burning coal. Some people like to say, “It’s only less than mammography etc” too, but again, you don’t swallow mammography. Breathing radioactive dust or eating radioactive food is like eating mammography machine and keeping it scanning inside of your body for several years.
According to MEXT, the radiation level in Tokyo used to be 0.036 μSv/h before 311. (cf, Radiation back ground level was 0.036 μSv/h in Tokyo before 311 [Link 1])If it’s higher than that now, it’s the radioactive dust. You breathe it, it comes into your eyes and ears to burn you from the inside directly on your mucous membrane.

Cesium or Iodine are radioactive material produced from nuclear reaction. Sometimes you can detect if something contains cesium or iodine by your geiger counter but mostly not. You need to take it to a lab and analyse. The amount of cesium or iodine in food is represented by Bq/Kg or Bq/L.
The safety limit is Zero Bq/Kg. Nobody says you can swallow burning coal if it’s a small amount.
Some people say, there’s nothing of Zero Bq/kg because of past nuclear test and Chernobyl etc.. but even when Chernobyl accident happened, food contained radioactive material only up to 0.1 Bq/Kg in Japan. Before 311, if something contained more than 100 Bq/Kg, it had to be treated as nuclear waste, had to be kept in controlled area. However now 100 Bq/kg is the safety limit of food.

ICRP is the sales department of international nuclear industry, but they decide you are not to be exposed to more than 1mSv per year.
The point is they don’t say you should not eat more than 10 Bq/Kg etc… Instead, they decided the formula to convert Bq/Kg into Sv. This is like “how much you have your stomach burnt if you swallow burning coal”, and this is decided for the political reason. From their political conversion rate, you are supposed to be safe even if you eat something of 100 Bq/Kg. There is no reason for the government to have to reply on ICRP, but because their safety regulation is very lax, it’s popular among nuclear governments.

(cf, ICRP underestimated the low dose symptom risk by 85% [Link 2])

There are many sorts of radioactive material but cesium, iodine and strontium are the most popular castings. Roughly speaking, cesium causes heart attack, iodine causes thyroid problem, and strontium causes leukemia. However, half of iodine disappears 1 week after nuclear reaction. so even if you take some pills of iodine now, it’s meaningless anymore. Also, if you find radioactive iodine from sewage sludge or something, it’s from recent nuclear reaction or medical usage.

At last, human body has about 70 Bq/Kg of potassium‐40. Potassium‐40 is a natural radioactive material, it’s even contained in bananas. Some people like to say “If you are scared of cesium, you can’t even eat bananas.” this is a traditional discussion. (These banana people were completely swept away in Japan during 2011, but still there are some in English area.) but human body (60kg) doesn’t have more than 4000 Bq/Kg, the amount is fixed, where radioactive cesium keeps being accumulated in your body. This is why cesium is dangerous.

Cesium accumulates in your muscle, and the biggest muscle in your body is heart. It keeps damaging your muscle cells. This is how it causes heart problems, but anyway, it’s washed out from your body one day. On the other hand, strontium accumulates in your bone, and the half-life is almost 30 years (Strontium90). It doesn’t go out of your body for longer than 30 years. Strontium is contained in food that has a lot of calcium, such as milk, cheese, and fish. However, Japanese government does not measure strontium in fish because it takes 1 month to analyze. so fish contamination is serious.

 

 

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Français :

[Édito] Que sont les Sv, Bq, césium, comment et pourquoi s’en soucier

On me demande souvent ce que sont les Bq/kg et Sv/h, etc. Je voudrais les expliquer de la façon la plus simple possible au monde.

Par exemple, si je hurle à ma fenêtre, ça ennuie mes voisins. Ma voix telle qu’entendue par mes voisins c’est, disons, 1  Sv = 1000 mSv = 1,000,000 μSv. et si on met son oreille directement contre ma bouche, ça sera plus fort. C’est le Bq.
A quel point ça vous agace, c’est le Sv, à quel point je fais du bruit, c’est le Bq.

Donc même si je suis à 10000000000 Bq/kg, si vous êtes très loin de moi vous n’entendez rien (0 Sv/h). D’un autre côté, même si je ne suis qu’à 1 Bq/kg, si vous êtes à moins d’un cm de moi, ça va vraiment vous gêner (100 Sv/h ou quelque chose comme ça).
C’est pourquoi vous ne pouvez pas utiliser un compteur Geiger pour savoir à quel point votre nourriture est contaminée. Ça ne vous montrerait que la quantité de radioactivité que le compteur est capable de détecter. Plus ça rayonne loin, plus la radioactivité s’affaiblit. Pour savoir à quel point c’est contaminé, on doit le faire analyser en laboratoire. Le résultat est en Bq/kg.

Ils disent que vous ne mourrez pas d’être exposés même à 2 Sv ou autre, donc même si vous détectez 0,2 μSv/h, c’est rien. Le truc, c’est de quoi proviennent les rayons. Après le 11-3, le Japon était recouvert de retombées de poussières radioactives. Si on détectait 0,2 μSv/h dans Tokyo, c’était par les cendres radioactives au sol. On peut détecter 20 μSv/h ou autre en posant le compteur Geiger directement sur les cendres puisque la radioactivité s’affaiblit quand elle se déplace, . Le problème est alors que vous pouvez en aspirer dans vos poumons.
C’est comme avaler des braises. Toucher des braises pendant un temps très court c’est rien mais si vous en avalez c’est une autre paire de manches. “Vous ne mourrez pas de 2 Sv” signifie que vous ne mourrez pas même si vous êtes à côté des braises, donc fondamentalement, vous ne pouvez utiliser votre compteur Geiger que pour savoir s’il y a des cendres radioactives autour de vous ou si une centrale nucléaire est en train d’exploser.

Selon la nature du sol ou l’ensoleillement, on peut détecter parfois des 0,2 et 0,3 μSv/h en certains endroits sur terre (c’est plus que d’habitude à Tokyo) mais on n’avale pas la lumière du soleil, pas plus qu’on ne mange les rayonnements radioactifs du sol. Ce n’est que la chaleur des braises. Certains se plaisent à dire aussi que c’est moins qu’une mammographie, etc. Mais, encore une fois, on n’avale pas l’appareil à mammographie. Respirer des poussières radioactives ou manger de la nourriture radioactive c’est comme avaler l’appareil à mammographie puis le laisser  scanner votre corps par l’intérieur pendant des années.
Selon le MEXT, le niveau de radioactivité de Tokyo était de 0,036 μSv/h avant le 11 mars. Si c’est plus haut que ça à présent, c’est à cause de ces poussières. (cf. Le bruit de fond radioactif était de 0,036 μSv/h à Tokyo avant le 11-3 [Lien1]) Vous pouvez en respirer, ça entre par vos yeux et vos oreilles et ça vous brûle de l’intérieur, directement contre vos  membranes et muqueuses.

 

Le césium et l’iode sont des éléments radioactifs issus de réactions nucléaires. Parfois on peut en détecter si quelque chose à proximité de votre compteur Geiger en contient, ce qui n’est pas le cas général. Vous devez l’apporter à un labo pour analyse. La quantité de césium ou d’iode dans la nourriture est représentée en Bq/kg ou Bq/L.
La limite de sécurité est Zéro Bq/kg. Personne ne vous dira que vous pouvez avaler des braises sans risque, même en toute petite quantité.
Certains disent que le zéro Bq/kg est impossible dans la nourriture à cause des essais nucléaires passés et de Tchernobyl, etc… mais même quand l’accident de Tchernobyl a eu lieu, la nourriture contenait seulement jusqu’à 0,1 Bq/kg au Japon. Avant le 11-3, si quelque chose contenait plus que 100 Bq/kg, on devait le traiter comme un déchet nucléaire, l’apporter à une zone contrôlée. Et maintenant 100 Bq/kg est la limite de sécurité de la nourriture.

L’ICRP est le département des ventes de l’industrie nucléaire internationale mais ils ont décidé qu’on ne doit pas être exposé à plus de 1 mSv par an.
Le truc, c’est qu’ils ne disent pas qu’on ne doit pas consommer plus de 10 Bq/kg, etc… Au lieu de ça, ils ont décidé de la formule convertissant les Bq/Kg en Sv. C’est un peu comme décider “à quel point votre estomac est brûlé si vous avalez des braises” et c’est déterminé en suivant des raisons politiques. Selon leur conversion politique, vous êtes supposés être en sécurité si vous consommez quelque chose vers 100 Bq/kg. Le gouvernement n’a aucune raison de s’en remettre à l’ICRP mais parce que leurs réglementations  de sécurité sont très laxistes, elles sont très prisées des gouvernements nucléaires. (cf. L’ICRP a sous-estimé à 85 % les risques des faibles doses [Lien2])

Il existe de nombreux types d’éléments radioactifs. Le césium, l’iode et le strontium sont les plus connus. En gros, le césium provoque des déficiences cardiaques, l’iode des problèmes thyroïdiens et le strontium des leucémies.
Pour l’iode, la moitié en a disparu une semaine après la réaction nucléaire, donc même si vous avalez des tablettes d’iode maintenant, c’est absolument sans effet. Inversement, quand on détecte de l’iode radioactif dans des boues d’épuration ou autre, il provient forcément d’une réaction nucléaire récente, ou d’un usage médical.

Au minimum, le corps humain contient environ 70 Bq/kg de potassium‐40. Le potassium‐40 est un élément radioactif naturel, on en trouve même dans les bananes. Certains disent que si vous avez peur du césium, vous ne pouvez même plus manger de bananes. C’est une discussion classique. (Ces “gens des bananes” ont complètement disparu du Japon durant 2011 mais il en reste toujours en zone anglophone) mais le corps humain (60 kg) n’en contient pas plus de 4000 Bq/Kg, cette quantité est fixée, alors que le césium radioactif peut s’accumuler bien plus. C’est pourquoi le césium est dangereux.

Le césium radioactif s’accumule dans vos muscles et le muscle le plus gros est le cœur. Il endommage les cellules musculaires. C’est comme ça qu’il induit les problèmes cardiaques mais, au final, un jour ou l’autre, il est éliminé.

De son côté, le strontium, qui a presque les mêmes propriétés chimiques que le calcium, se fixe et s’accumule dans vos os. Sa demie-vie est d’environ 30 ans (strontium 90). Il faut plus de 30 ans pour l’éliminer. Le strontium se trouve dans les aliments riches en calcium, les lait, fromage et poisson. Ceci étant, le gouvernement japonais ne mesure pas le strontium des poissons parce qu’il faut 1 mois par analyse. Donc la contamination des poissons est sérieuse.

  1. Excellent explanation. The other problem with knowing what Bq is, is there is nothing to compare it to. We know what one cow is, but we don’t know what one Bq means. Thanks for the info!

    1. This is already getting quite complex very fast.

      Bq is the amount of radio active decays per second.
      If you have a geiger counter, each click you hear is one radioactive decay. So if you hear one click per second, you have 1 Bq from the material you’re measuring.

      These Bq’s can be used to calculate the dose of radiation you receive (which is measured in Sievert). However the conversion from Bq to Sv is not simple, because it depends on the material that is actually radioactive.

      For example: 1 Bq from pollonium, which was used to poison Russian spy Alexander Litvinenko, makes you more annoyed (and thus has a higher value in Sieverts) then 1 Bq from cesium-137 does.

      So to fully understand how much radiation you get from your food and how harmfull it really is, you’d have to do an analyses with a geiger counter and do a chemical analysis to figure out which material you’re dealing with.

      To make matters even worse, there are a LOT of factors you have to take into account when using a geiger counter to measure the contamination of food. So measuring the dose of radiation you receive is way beyond a normal person’s capabilities.

      So what do we know?

      We know that in fact the system of using Sieverts is actually a better system if you want to measure the danger and effect of radiation on humans, but it’s also a lot harder to measure, use and calculate.

      And we know that the simple personal geiger counter cannot be used to figure out how much radation you receive or how contaminated food actually is. However, it can be used to get an indication about wheter or not the food you’re going to eat is contaminated.

      If you want to test the last thing, you’d basically have to turn on your geiger counter for 5 minutes and note down the readings you get.
      After those first five minutes, you have to put the food (or the ingredients) very close to your geiger counter and wait another five minutes. If the readings you get from it now are about the double or triple of the readings you got when the food (or another object) wasn’t near the counter, this might be an indication that this food is contaminated.
      As you can see, this takes a lot of time and patience…

  2. HAARP Magnetometer Data Shows Japan Earthquake Was Induced
    “HAARP was broadcasting the 2.5 Hz frequency from just before midnight on March 8, 2011 and continued to broadcast the frequency for the entire days of March 9, 2011 and March 10, 2011. The 2.5 Hz frequency continued to be broadcasted and recorded by the magnetometer for another 10 hours the day of the Japan 9.0 magnitude earthquake.

    You will notice on the USGS website that the Japan earthquake didn’t occur on the Ring of Fire Fault line. The epicenter was some 100 km west of the fault. The earthquake epicenter occurred on solid ground.”

    http://theoldspeakjournal.wordpress.com/2011/03/25/haarp-magnetometer-data-shows-japan-earthquake-was-induced/
    via
    http://mrmaxbliss.wordpress.com/2013/01/21/91/

  3. You say 100 Bq/Kg was nuclear waste?? I thought the old limit in food was much higher.

    http://blogs.wsj.com/japanrealtime/2012/03/29/toward-a-lower-cesium-diet/

    “The limit for drinking water will fall to one-twentieth of what it had been. For most foods, the new level will be one-fifth the old limits. Japan’s new standards will also include a separate, lower level for food given to infants, who, researchers say, are the most vulnerable to the effects of radiation.

    Japan’s new permissible level for drinking water, 10 becquerels per kilogram, is lower than that for milk, at 50 becquerels per kilogram, since the government assumes people will drink more water than milk.”

    It’s still high in Europe and the US.

    “The U.S. and European Union each have their own standards that permit considerably higher levels of radioactive cesium than Japan does. Their rules vary widely – both in how food categories should be grouped and in levels of radiation permissible. U.S. food-safety restrictions wouldn’t go into effect, for instance, until 1,200 becquerels of radioactive cesium had been detected per kilogram. The EU’s standard for radiation in food in the case of future nuclear accidents has one limit for liquids — 1,000 becquerels per kilogram — and another for other kinds of foods — 1,250 becquerels per kilogram.”

    It was an excellent explanation otherwise.

    I also think of Bq as like the earthquake magnitude (absolute energy amount) and Sv as the Shindo (the damage, the motion depends on how close you are).

    1. 1. There are double standards.
      2. You don’t actually have radiation in food like current Japan.

      1. 3. That 1,250 Bq/Kg rule is actually for the potential nuclear war time, which may end in relatively short time. It doesn’t consider how much of cesium accumulates in your body if you keep eating it for a long time -over decades in Japan.

  4. Sr90 takes long to measure?
    NO!
    Independent People use the
    AT1315 Gamma Beta Radiation Spectrometer
    It can measure Stronium 90 in Food.
    State does not tell the people this fact.
    PARENTS!
    EMPLOYED!
    UNEMPLOYED!
    TEACHER!
    STUDENTS!
    UNITE!
    If everyone donates!
    You can buy these devices!
    Set up in public places like schools!
    For free!
    For everyone!
    All the time!
    Do not trust the Government
    Do not trust Dose limits
    They mean: MURDER of the Genetic Code

    For a CLEAN Future!

    1. Buying this kind if equipment is not the problem.

      Finding people that can make sense of the data this kind of equipment provides is the big problem, because Radiation Spectrometry is not a skill that’s very common among the regular people. There might only be 3000 people in Japan who have actually mastered that skill and know how to make sense of the data! Most of them will be professors and reasearchers at companies or universities.

      Also, you might want to question if you actually want people bringing potentially radioactive materials into public places like schools. (I certainly wouldn’t want that to happen).

      I live in a country that felt the effects of the Chernobyl disaster and know from experience that it will probably be 4 to 5 years before the problem of radiation will not be a big issue anymore.

      Also, Japan has quite some experience with nuclear dead zones from the Nagasaki and Hiroshima bombings. The country just has to hold on for a couple more years and it will be fine.

      In the meantime, you might want to close down some of those nuclear powerplants though….
      An obvious alternative to those would be to start using some of the volcanic potential the country has. Ironically, only the government of Japan would be big enough to start such a project.

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About this site

This website updates the latest news about the Fukushima nuclear plant and also archives the past news from 2011. Because it's always updated and added live, articles, categories and the tags are not necessarily fitted in the latest format.
I am the writer of this website. About page remains in 2014. This is because my memory about 311 was clearer than now, 2023, and I think it can have a historical value. Now I'm living in Romania with 3 cats as an independent data scientist.
Actually, nothing has progressed in the plant since 2011. We still don't even know what is going on inside. They must keep cooling the crippled reactors by water, but additionally groundwater keeps flowing into the reactor buildings from the broken parts. This is why highly contaminated water is always produced more than it can circulate. Tepco is planning to officially discharge this water to the Pacific but Tritium is still remaining in it. They dilute this with seawater so that it is legally safe, but scientifically the same amount of radioactive tritium is contained. They say it is safe to discharge, but none of them have drunk it.

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