Fears of radiation in Japan

Having recently traveled near the nuclear-impacted Fukushima region, we watched the Japanese media hyping up the story of the day.  Apparently, grain from Fukishima farmers had been harvested and mixed into the feed supply for cattle, resulting in the discovery of beef samples with higher than usual levels of radiation.

On the surface, this sounds like legitimate news.  But when you dig into the numbers, it starts to look like paranoia.  Most frustrating of all is the media’s inability to deal with numbers.  Do journalists skip math classes?  I can’t understand why even the best news sources (the New York Times, for example) gloss over numerical facts in favor of quotes and human interest angles.  For news coverage of this type of story, there’s only one thing that matters:  scientific evidence accumulated by generations of nuclear scientists.

So I dug up some sources which do a better job.

The contaminated beef has very low levels of radiation.  Eating the worst sample tested would result in less radiation than a person would receive during a flight from NYC to Tokyo (and that’s only if you can eat a 2 pound steak).

As of Thursday, the most highly contaminated beef found contained radioactive cesium of 4,350 becquerels per kilogram, according to the Health, Labor and Welfare Ministry. The meat did not reach the market.

Eating 1 kg of the meat is roughly equal to a radiation dose of 82.65 microsieverts for a period during which radioactive cesium remains in one’s body. If a person eats food with radioactive cesium, half the amount remains in the body for nine days for a baby younger than 1. But the duration gets longer as people age, and it takes 90 days for those aged 50.

The 82.65 microsieverts compares with the 100 microsieverts of radiation a person would be exposed to during a one-way flight from Tokyo to New York.

From JapanTimes 

Now that being said, radiation is extremely dangerous in large doses.  People should not be near the nuclear plant without protective gear.

The most heavily contaminated spot was in the town of Okuma about two miles southwest of the plant, where someone living for a year would be exposed to 508.1 millisieverts of radiation — far above the level of 20 millesieverts per year that the government considers safe.

From NYT

Another useful comparison is the radiation received during chest Xrays.  For example, nuclear workers are not supposed to receive more than 2 chest Xrays worth of radiation per year.

100 millisieverts (mSv)-a millisievert is a unit of radiation dose equivalent to about 10 general chest X-rays. This dose is about five times the maximum annual dose limit currently permitted for workers in nuclear facilities (20 mSv per year). Average worldwide natural “background” radiation is about 2.4 mSv annually.

Fewer than 10 percent of the 116,000 people evacuated from the “exclusion zone” received doses greater than 50 mSv; fewer than 5 percent received more than 100 mSv.

from IAEA 

And of course smoking is far worse than any light exposure to nuclear radiation.

Some consumer products are also sources of radiation. A person who smokes two packs of cigarettes per day receives 8,000 mrem per year. Smoke detectors produce about 1/100 mrem per year. Certain household appliances such as color television sets and microwave ovens also produce very small amounts of radiation. On the average, consumer products account for about 3 percent of our annual exposure.  [note:  1 rem = 0.01 Sv]

From US Army 

And for those paranoid countries that are turning off their nuclear reactors out of fear of another Fukushima, note the comparison with living near a coal plant coal:

Average annual radiation dose is 360 millirems per person. 300 from natural sources.

Coal plant, living within 50 miles: .03 mrem
There is much thorium and uranium in coal. Living within 50 miles of a nuclear power plant adds .009 mrem of exposure. Both figures are considered extremely low levels.

Smoking: up to 16,000 mrems

Living on the Earth: 200 mrems

From PBS