Fear and uncertainty continue to grow around the condition of Japan’s Fukushima Daiichi nuclear power plant. There has been a fervent struggle to keep the plant’s reactors from achieving a partial or complete meltdown after the devastating earthquake in Japan and Pacific tsunami damaged the plant and knocked out the backup power needed to cool its radioactive fuel rods.
Naturally, the events in Japan have people curious, frightened and confused about the potential impact of not only the Fukushima plant’s radiation, but on the impact of nuclear power plants and radiation in general on the body. Even friends have asked me if they should evacuate the U.S. West Coast just in case radiation from Japan travels across the Pacific Ocean.
Until now, I haven’t had a good way to explain why they shouldn’t worry about radiation from Japan, especially given the many other sources of radiation we encounter on a daily basis. However, Randall Munroe of XKCD has solved that problem by putting together a very informative chart explaining and visualizing radiation doses and their sources. Although we don’t suggest living by this chart, it’s a good general education tool for understanding the effect of radiation absorption.
We encounter sources of radiation every day, from natural background radiation to bananas. (Yes, bananas emit gamma rays, but you’d have to eat 5 million bananas in one sitting to get any kind of radiation sickness.) The absorption of this radiation is measured in units called the sievert (Sv). As the chart explains, we absorb approximately 0.1 microsieverts (μSv) of radiation per day from eating a banana, 10 μSv from background radiation and 20 μSv from a chest x-ray. That’s more than the radiation you’ll absorb from living within 50 miles of a power plant (0.09 μSv). Even a coal power plant generates more radiation (0.3 μSv) because coal has trace amounts of uranium.
It takes a lot more radiation to actually cause harm to a person, although, the maximum yearly dose permitted for a U.S. radiation worker is 50 millisieverts (mSv), more than 200 times the exposure received from a typical X-ray. It takes double that amount though (100 mSv) for an increased risk of cancer and a full 2,000 mSv for severe radiation poisoning to occur.
For a more detailed explanation of radiation dosage, check out the XKCD chart below. Click on the image to see a full-sized version: