This table links radiation dose to radiation risk in a way that's a bit more clear. It was put together for BoingBoing by Kelly Classic, public outreach coordinator for The Health Physics Society, and a radiation physicist at The Mayo Clinic. I'm going to try to get it converted into something prettier and more infographic-y later.
Some important points to go along with this chart:
• The risks of radiation exposure are radiation sickness, and/or increased lifetime risk of cancer. Only people receiving very high doses develop radiation sickness—the Fukushima 50, working inside the power plant, are at risk of this. Somebody in Tokyo is not.
The other risk—an increase to the victim's lifetime risk of developing cancer—is a lot more complicated. Key thing to remember: On an individual basis, it's an increase in risk, not a promise that cancer will develop. And it has to be understood in context with already existing cancer risks. In the footnotes of the chart, Kelly Classic points out that the average American has a 42% risk of developing (not dying from) some kind of cancer in his or her lifetime. If one of us gets hit with a 300 rem dose of radiation—a high enough dose that we'd have symptoms of radiation sickness—we'd see our lifetime risk of cancer increase to 42.03%.
• When this table says "n/a" under the risk heading, that's not because the information isn't available. It's because, at that dose, the health effects are so small as to be unmeasurable.
Radiation dose and risk works on what Ralf Sudowe, professor of health physics and radiochemistry at the University of Nevada Las Vegas, calls "linear no threshold." Scientists assume that any amount of radiation—no matter how small—carries some risk. They also assume that the risks increase linearly, along with the dose.
But, Sudowe (as well as Kelly Classic, and the other health physicists I've spoken to) also say that, even though radiation isn't safe at any level, that doesn't mean there's reason to panic at every level. At low enough doses, scientists can no longer find evidence of an increased rate of cancer. And that's pretty much the point where we don't have to worry.
• Time also matters. "A high exposure given in a short time (minutes, hours) that could cause a harmful effect may not do anything if given over years because our body adapts and our cells repair minor damages," Kelly Classic says. "So if I was exposed to 500 mSv in a period of minutes, my blood would show some changes, but if I was exposed to 500 mSv over 50 years, I'd have an increased risk of cancer, but no discernible signs of radiation exposure [meaning no radiation sickness].'
Image used on http://www.boingboing.net/sci page is Yuriko Nakao / Reuters.
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