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Dr. Tsubokura's Radiation Lecture Vol.30

Author: Masaharu Tsubokura

Editors: Akihiko Ozaki M.D., Yuki Senoo

59. The health effects of external exposure received during walking through high radiation areas are small

Microsievert/h is a unit of air dose rate used in radiation dosimeters. It indicates the doses from external exposure received while spending 1 hour in the measurement area.

Hence, we can estimate the actual external radiation dose by multiplying the air dose rate by the amount of time spent. For example, when you stay in the area with 0.2 microsievert/h for 5 hours, the actual external radiation dose will be 1 microsievert (0.2 x 5).

In comparing air dose rates in locations where people spend long periods of time versus where they spend just 2-3 minutes, which one do you think will contribute more to the total external exposure?

The answer is external radiation dose depends mainly on the air dose rates in locations where people spend the majority of their time unless the air dose rates of the areas in which they stay for a few minutes are exceptionally high. This is because time duration is 100 times different between the two cases.

Total radiation dose determines the health effects of radiation exposure. The air dose rates in locations where people spend long periods of time on a daily basis, such as residential areas and school, affect the total radiation doses from external exposure. In contrast, the radiation exposures received from passing through high radiation areas present a small health risk.

60. “Radiation exposure risks” of driving down Japan National Route 6

Radiation dosimeter is a device used to measure air radiation dose rate, which is the level of radiation exposure received while spending 1 hour in the measures of location. The actual exposure dose is estimated by multiplying the air dose rate by the duration of time spent. This means that we can reduce the total radiation dose by shortening the time spent even in locations with a high air dose rate.

For example, the radiation exposure received while driving through Japan National Route 6 near Fukushima Daiichi Nuclear Power Station for 40?km from Naraha-machi to Minami-Soma City is approximately 1.2 microsieverts (measured in 2014). It is less than 1/50th of the amount of exposure received from a chest X-ray and is less than 1/100th of the radiation exposure received during a round-trip flight between Narita Airport and the United States.

The exposure dose will be even lower if you drive through Joban Highway, a road that is even more distant from the power plant than Japan National Route 6.

The extent of the total exposure dose determines the health impacts of radiation exposure. The example of Japan National Route 6 demonstrates that you will not receive a high level of radiation exposure simply from passing through a place with high air dose rates.


The Japanese version of the manuscript was originally published in Fukushima Minyu, a local newspaper in Fukushima prefecture, Japan, on February 21st and 28th 2016 was reproduced for MRIC Global under the author's permission.

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