Don’t worry, be happy, it’s all just a matter of scale…

As I mentioned in my last post, the interwebs are a fantastic asset to spreading information. Information, after all, wants to be free to spread itself in the wild. One of the downsides of this fantastically efficient network of ours is the spread of information that is alarmist or even false.

Consider this article that a very concerned friend sent me the other day: The Radiation Warnings You Won’t Get from the Mainstream Propaganda Machine

scary greenpeace image

Aside from the fact that it is poorly researched muckraking, with little to no sourcing of information, it is totally designed to play on our lack of scientific understanding.


Samples of milk taken across the United States have shown radiation at levels 2000 percent higher than EPA maximums. The reason that milk is so significant is that it it representative of the entire food supply. According to an article published on Natural News, “Cows consume grass and are exposed to the same elements as food crops and water supplies. In other words, when cows’ milk starts testing positive for high levels of radioactive elements, this is indicative of radioactive contamination of the entire food supply.”

Follow the article to Natural News and they begin reporting things like “Fukushima radiation taints US milk supplies at levels 2000 percent higher than EPA maximums” They source their data, which is a good thing. The first problem is more that the data is now over a year old. The second problem is that most people don’t really understand radiation contamination levels in any meaningful way.

Ask yourself, do you know what pCi/L means? More than likely you had no idea it stands for picocuries per liter. Even if you did happen to know that definition, which I will confess I did not remember it from my last Physics class at Berkeley more than 20 years ago, you almost positively had no idea that it stands for one trillionth of a curie.

The basis for the curie is the radioactivity of one gram of radium. Radium decays at a rate of about 2.2 trillion disintegrations (2.2×1012) per minute. A picocurie is one trillionth of a curie. Thus, a picocurie (abbreviated as pCi) represents 2.2 disintegrations per minute. To put the relative size of one trillionth into perspective, consider that if the Earth were reduced to one trillionth of its diameter, the “picoEarth” would be smaller in diameter than a speck of dust. In fact, it would be six times smaller than the thickness of a human hair.

Now the interesting thing about stating the risk in terms of picocuries is that you cannot convert that to sieverts. This is because pCi (picocuries) and Sv (sieverts) are not compatible. We use sieverts to quantitatively evaluate the biological effects of ionizing radiation as opposed to just the absorbed dose of radiation energy, which is measured in grays.

unit dimensions common physical quantity
pCi (picocuries) 1/[time] radioactivity
Sv (sieverts) [length]^2/[time]^2 equivalent dose of ionizing radiation

The reason you cannot compare the two has to do with the time component to sieverts that is used to establish the risk of harm from exposure to radiation. By comparison, picocuries only tell us an amount of radiation at period time-1 and cannot tell us anything about the biological impact of exposure over time.

Where does this leave us? Well, at least one of the reasons why radiation is so scary for most people is that it is invisible (and of course potentially deadly). This invisible “threat” can be as terrible as the fallout from Fukushima ( 40 mili-sieverts ) or as harmless as eating a banana ( 0.1 micro-sieverts ). In fact, when I go to the dentist’s office I refuse to wear a lead vest when getting dental x-rays. This usually scares the shit out of the oral hygienists. Silly right? The average dental x-ray is 5 micro-sieverts and my flights from Boston to San Francisco ( one way ) which I make 8 to 10 times a year are exposing me to 40 micro-sieverts EACH time I fly. Perhaps I should get Virgin America to give me a lead suit to wear!

( See the wonderful chart at XKCD for a better understanding of Radiation dosages ).

The bottom line is that radiation may be invisible, but it is not magic. With an application of the right medium and an understanding of the physics involved, we can (indirectly) see radiation happening in real-time ( see cloud chamber video below ). Perhaps if we expand our understanding of radiation we will be less afraid and less susceptible to the fear mongering and muckraking of the interwebs.

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