Radiation Fears May Be Greatly Exaggerated

Levels at present are 'no cause for concern,' say experts

They are hoping to get their hands on potassium iodide pills to protect them from radiation — despite warnings that, in the absence of a real nuclear threat, taking the medicine is riskier than doing nothing

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Sixty-six years after the first atomic bomb exploded over the city of Hiroshima, radiation spooks people everywhere. But the anxiety is largely disproportionate to the actual danger.

How much radiation is dangerous?

1. Radiation is measured using the unit sievert, which quantifies the amount of radiation absorbed by human tissues. One sievert is 1,000 millisieverts (mSv).

   In the U.S., the average person is exposed to about 6.2 millisieverts a year, mostly from background radiation and medical tests.

   Some facts about radiation exposure:

   • A person would need to be exposed to at least 100 mSv a year to have an increase in cancer risk. Exposure to 1,000 mSv during a year would probably cause a fatal cancer many years later in five out of every 100 people.
   • Total body CT scan: about 10 mSv.
   • Mammogram: about 0.7 mSv.
   • CT colonography: about 5 to 8 mSv.
   • CT heart scan: about 12 mSv.
   • Typical chest X-ray: about 0.02 mSv
   • Dental X-ray: 0.01 mSv.
   • Coast-to-coast airplane flight: about .03 mSv. Airline crews flying the New York-Tokyo polar route are exposed to 9 mSv a year.

   Sources: Reuters; New England Journal of Medicine; American Cancer Society; World Nuclear Association and Taiwan's Atomic Energy Council

"People in general have an exaggerated fear of radiation. That is true in the United States, and it is probably even more so in Japan," said Jerrold Bushberg, director of health physics programs and clinical professor of radiology and radiation oncology at the University of California Davis.

Despite the Japanese government's assurances that the risk so far is minimal, residents of Tokyo have flooded out of the city and foreigners have fled the country, hoping to escape a threat they cannot see.

The fact is that everyone is exposed to small amounts of radiation every day just from living on earth or flying in an airplane. That all adds up to about 2.4 units, known as millisieverts, a year. This can vary widely, ranging from 1 to 10 millisieverts, depending on where you live.

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