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Dr. Tsubokura's Radiation Lecture Vol.2

Author: Masaharu Tsubokura

Editors: Izumi Yoshida, Mariko Irie, Yuki Senoo

3. The higher the altitude, the higher the radiation dose

Before the nuclear accident, from where in the surrounding environment did you get exposed to radiation? The universe and the earth emit radiation, and the air and food contain radioactive substances.

From space, we get radiation called cosmic ray falls. When you fly into the sky in an airplane, radiation will increase as the air becomes thinner. Pilots and cabin attendants get more radiation than people on the ground. Compared with when you are on the ground, you may receive radiation more than several dozen times per unit of time depending on flight altitude; however, there is no report that health has been compromised. In one day, an astronaut may even get the equivalent of more than one year’s worth of radiation on the ground.

Exposure by cosmic rays is 0.39 millisieverts per year on average worldwide. It accounts for about 16% of the total exposure from the surrounding environment.

4.Radioactive substances in food

Human beings, animals, plants, and foods contain radioactive substances from before the nuclear accident. An essential element for maintaining our life is potassium; however, a small part of potassium emits radiation as radioactive potassium, and it exists in every muscle, the earth, concrete, etc. The half-life is also overwhelmingly over 1.2 billion years.

For example, if you drink a cup of milk and eat a banana for breakfast, it means that you take in 20 Bq (becquerel), and a bottle of beer and potato chips in the knob will contain about 40 Bq of radioactive potassium.

We do not need to say, “Let’s not eat it, then” or “Since potassium is natural, there is no problem.” Radioactive substances of dozens of becquerel taken in everyday life are not enough to affect the body, and the difference of whether or not our body ingest them does not affect our health.


The Japanese version of the manuscript was originally published in Fukushima Minyu, a local newspaper in Fukushima prefecture, Japan, on January 25 and February 1, 2015, and was reproduced for MRIC Global under the author's permission.

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