Basic Facts on Annual Radiation Levels in the U.S. and in Tokyo . . . and Why There is No Need for Panic at This Time (by Junichi Taguchi, MD)

To those who live in the Tokyo area and are concerned about radiation exposure:

Please refer to an article below written by Dr. Junichi Taguchi, Clinic Director of Tokyo Midtown Medical Center. The clinic has been receiving many inquiries regarding radiation exposure. Some are even requesting potassium iodine. While concern is understandable and the situation should be monitored carefully, Dr. Taguchi explains there is no need to panic at this time.

Basic Facts on Annual Radiation Levels in the U.S. and in Tokyo, and Why There is No Need for Panic at This Time

It is widely known but not so well understood that we are exposed to certain amounts of radiation on our daily lives.  Radiation comes from numerous sources such as radon, radiation in our soil, cosmic radiation, medical devices.  (Please see the list at the end of the article for a comparison of radiation sources and estimated radiation levels in the U.S. and in Tokyo.)

According to radiationanswers.org, individuals who frequently fly often wonder about the extra radiation exposure they receive during flights. The amount of radiation received depends on several aspects, including the length of the flight, the altitude reached during the flight, and of course, the frequency of travel. Some of the approximate doses when flying at 36,000 feet are:

• New York to Los Angeles round trip = 4 mrem
• New York to Paris round trip = 6 mrem
• New York to London round trip = 6 mrem
• Los Angeles to Paris round trip = 10 mrem
• Los Angeles to Chicago round trip = 2 mrem

Annual radiation exposure in US is 360 mrem, or 3.6 mSv.  In Tokyo, it is 235 mrem, or 2.35mSv.  The difference in the two numbers is due mainly to the difference in radon concentration and man-made sources such as medical x-rays.  

In Tokyo, the current fall-out radiation from Fukushima is less than 0.1 micro Sv per hour. Calculated as an annual amount of extra radiation, this is no more than 0.1 micro Sv/hr  X  24 hr X 365 days = 876 micro Sv = 0.88 mSv.

So, if the current radiation level were to continue for a year, the total estimated annual amount of radiation in Tokyo will be at most, 2.4 mSv (annual average) + 0.88 mSv (extra radiation) = 3.28mSv.

It should be noted that calculation of the extra radiation on an annual basis is a very conservative estimate, as radiation levels in Tokyo are falling daily, and the current situation is not expected to last for a whole year.

In essence, this conservative number is still less than average annual radiation exposure in US, and is not a cause for panic.


Annual U.S. Estimated Radiation Dose Per Person/Source/Average annual effective dose (mrem)

Radon and other radionuclides we eat, drink, or breathe   240
Radiation from soils, rocks, building materials  30
Cosmic/cosmogenic radiation  30
Human-made sources   60


Total  360


Annual Estimated Radiation Dose Per Person in Tokyo, Japan/Source/Average annual effective dose (mrem)

Radon and other radionuclides we eat, drink, or breathe  75

Radiation from soils, rocks, building materials   30
Cosmic/cosmogenic radiation  30
Human-made sources  100

Total  235

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