Radiation Chart Update

Ellen and I made our radiation chart in the early days of the Fukushima disaster. I intended it to provide context for radiation exposure levels reported in the media.  I included a few example doses from monitoring sites around Fukushima (the only ones I could find at the time). But our main goal was to give people a better understanding of what different radiation levels meant.  It wasn’t a guide to what was happening at Fukushima because neither of us had hard data on that.

I’ve recently corrected a few things on the chart (the old version is available here). In particular, I’ve changed the mammogram dose from 3 mSv to 0.4 mSv, based on figures from this paper.  The other figures seem to hold up, and I’ve made only small corrections elsewhere.  I’ve added a few more Fukushima-related doses where I could find data, but they’re examples only—not full coverage of the effects.  Specifically, I added total exposure figures over the weeks following the accident for Tokyo, a typical spot in the Exclusion Zone, and a station place on the northwest edge of the zone that got a particularly heavy dose. Those data came from here (Google cache of now-dead MEXT page) and here.

Unfortunately, the disaster has progressed beyond simple radiation releases—there’s some amount of contaminated water, and radioactive material potentially getting in food. When radioactive material is ingested, the effects get a lot more complicated, and depend on what isotopes are there and how they’re processed by the body. Ellen’s page has a bit more information about that.

For reliable information on what’s happening in Japan, including discussions of the contamination levels, there are two sites Ellen and I recommend. One is the MIT Nuclear Science and Engineering hub, which posts periodic articles explaining aspects of the disaster, and the other is the International Atomic Energy Agency’s Fukushima Accident Update Log, which has detailed measurements from a variety of sources.

Note: Some people questioned the side-by-side comparison of short- and long-term doses.  It’s true that they’re not always the same, and I mentioned this in the intro note on the chart. Combining the two sacrificed precision for simplicity, but I don’t think it was a huge stretch—most regulatory dose limits are specified in terms of a total yearly (or quarterly) dose, which is a combination of all types of exposures.  And for those low doses, the comparison is pretty good; the place duration becomes important is up in the red and orange zones on the chart.

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