Sievert and Becquerel, Oh Dear!

So the Georgia Straight sort of tries to clarify things in this article, and not surprisingly, fail miserably.

The article starts out pointing out how confusing all the data is, then does nothing but muddify the fuzzification (as Dr. Foth used to say) by throwing out more random numbers and units lacking context, and never once mentioning what the units mean. They complain that Environment Canada’s data is confusing, but do nothing to provide more clarity. The impression they leave is that Health Canada, by releasing the radiation data from Fukushima, is actually involved in a conspiracy to cover it up.

I already talked about Becquerel, so you should realize that the exposure listed in the following quote is one millionth of the exposure you receive from your own bones:

” The level of iodine-131 in Sidney, B.C., rose to a high of 3.63 milliBecquerel per cubic metre in the air on March 20. That’s over 300 times higher than the background level of 0.01 milliBecquerel per cubic metre or less.”

Oh, and that “background” value? There is no natural background value for Iodine 131, it is not a naturally occurring element in any quantity (it is a product of uranium fission), and has a short half-life (8 days) in real-world terms, so any of it that is created naturally goes away really quick. What they are falsely calling “background” is actually the Method Detection Limit (“MDL”), or the smallest concentration that can be detected using the equipment available. Note that Cesium-137, later in the article, has the same “background” concentration.

It is interesting to note that the acceptable level of Radon in your home is 200 Becquerel per cubic metre. So your daily exposure in your home, where you breathe 8 hours a day 365 a year is not significant health concern at 50,000 times the level of that one-day spike in Sidney.

But what about Sievert? According to the article:

“It’s a shell game. MicroSieverts are quite a distance removed from the raw data. They’re blending in stuff from nature to make the data look innocuous,”

. This is one of the most ignorant anti-science statements I have read in printed media in a long time. Sieverts confuse this poor idiot, so he assumes someone is pulling the wool over his eyes. We are not too sure who, and what their nefarious plan is, but this writer is finding conspiracy every time someone uses a term he does not understand. Instead of trying to understand it, he assumes the worst. That is the difference between skepticism and cynicism.

It really isn’t that complicated, and if he did a little research, he would discover that the calculation of “effective dose” does the exact opposite of what he says: it combines together the cumulative impacts onto a single unit, allowing us to compare radiation apples to radiation oranges.

Not all radioactive substances are the same. When they decompose, they release various different types of radiation and/or particles. So in that sense, a counting of Becquerel (like I have been doing for the last two posts) tells us about the amount of atom decay, but does not tell us about the harm each decay may cause.

When an atom of Potassium-40 in your bones decays, it (most often) releases an electron at very high energy (<1.3meV), and a neutrino. The neutrino is harmless (or at least it is drowned out by the 60+ billion of them that pass through every square centimetre of your body every second you are alive on earth) but the electron at that energy level is called a beta particle, and is a form of ionizing radiation that can cause cellular damage. When Iodine-137 decays, it does a little two-step decay that results in a beta particle followed very shortly by a gamma ray. Uranium-238, in contrast, releases an entire helium nucleus, otherwise known as an alpha particle. Each of these particles pack a different “punch”, a they carry different abilities to interact with other materials.

The unit “Grey” is used to convert the varying doses delivered by a unit of each of these types of radiation into one convertible unit. It is a little more complicated than this, but essentially, because an alpha particle is bigger and interacts more strongly with other materials, it packs 20x the “dose” of a gamma ray or a beta particle (which pack about equal doses). So one unit of alpha radiation packs the punch of 20 units of gamma or 20 units of beta. It also stands to reason that these three types of radiation (alpha, beta and gamma) are differently harmful to health. Alpha particles are big and heavy, so they cannot penetrate your skin very far (only a few micrometres), and actually can only travel a few metres through the air before being absorbed by the atmosphere. Therefore, direct exposure to alpha radiation tends to cause things like radiation burns. Beta particles are smaller, with more energy, and can travel through the air pretty freely, but only penetrate several centimetres into your skin, causing deeper damage. Gamma rays can pass through most materials (although lead does diffuse them quite a bit) and since they can pass right through your body, tend to cause systemic “radiation sickness” if you are exposed to a lot of them.

To further complicate matters, some tissues in your body (especially your bone marrow and lymph nodes) are more severely impacted by radiation than other tissues (like the skin or the liver). A single Grey of exposure will impact your lymph nodes more than your skin, so factors that account for these differences need to also be calculated if we want to understand the health effects of radiation. As the ultimate impact on your body are cumulative from all of the tissues affected, these tissue-specific factors are added together, and the sum value used to calculate the “effective dose” a person receives from any given amount (Grey) of radiation.

Since we are comparing three different types of radiation and dozens of different tissues, the unit must be standardized. The “effective dose” is measured in the Si unit “Sievert”, which is defined as the amount of radiation that has the equivalent biological impact as one joule of gamma rays adsorbed by one kilogram of tissue. You can look at this data table to put that number into perspective. The average North American is exposed to about 3 milliSievert (mSv) every day from natural sources (or 0.003 Sv), and can receive from 0.004 to 0.83 mSv from a medical or dental x-ray.

A microSievert is 0.001 milliSievert. So the radiation “spikes” mentioned in the Georgia Straight article, from 0.43 to 0.48 microSievert, or 0.23 to 0.25 microSievert, or even 0.36 to 0.96 microSievert, are much less than a thousandth of our daily exposure from things like the uranium in our granite countertops to the radium adsorbed in our rain to the potassium in our bananas (and notably, not the radio waves from our cell phones). And less than a hundredth of the exposure we would receive from a single dental x-ray.

The article does sum up with one of those great meaningless quotes: “There is no safe level of radiation.” I would suggest anyone in BC concerned about their increased exposure to radiation caused by Fukushima should probably eat one less banana this year, and you will more than offset any impacts

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