There are two types of radiation exposure.
Exposure to radioactive materials released in the environment and absorbed in the body by ingesting contaminated food/water or by inhaling contaminated air. The exposure to radioactive materials released in the environment due to nuclear accidents, including the Chernobyl and the Fukushima No.1 nuclear power plants, are examples of this type.
External exposure and internal exposure
1. External exposure to radiation
“External exposure” means exposure to radiation, mainly neutron rays and gamma rays, from sources outside the body. The unit used for measured radiation is “sievert” (Sv). One milisievert (mSv) is 0.001 Sv. One microsievert (μSv) is 0.001 mSv.
2. Internal exposure to radiation
“Internal exposure” means exposure to radioactive materials absorbed in the body by ingesting contaminated food/water or by inhaling contaminated air. These materials remain in the body and keep emitting radiation. The unit used for measured radioactivity is “becquerel” (Bq).
Different radioactive elements accumulate in different parts of the body. For example, radioactive iodine accumulates in the thyroid gland, cesium in the muscle and other parts of the body, and strontium mainly in the bone marrow. If these radioactive materials are absorbed and remain in the body, they damage health because they continue irradiating and cause harm to the surrounding tissues and organs.
– Physical half-life of radioactive materials (the time required for half of the amount of radioactive material to decay)
- Iodine-131 (131I) – 8 days
- Cesium-137 (137Cs) – 30 years
- Strontium-90 (90Sr) – 28 years
– Biological half-life of radioactive materials (the time required for half of the amount of radioactive material absorbed in the body to be naturally eliminated)
- Iodine-131 (131I) – about 3 to 4 months
- Cesium-137 (137Cs) – about 100 days
- Strontium-90 (90Sr) – about 50 years
Workers who deal with radiation and the general public
Workers who deal with radiation or aid at accident sites are at risk of both internal and external exposure to radiation. The permissive level of radiation for these workers is 100mSv per five years, and 50mSv per year. (This permissive level has been raised to 250mSv for the workers at the nuclear power plant in Fukushima.)
As for the general public, unless people go near radiation sources, the risk of external exposure is rare, but they may be exposed to internal exposure of radiation released in the environment. The permissive level of radiation for the general public is 1mSv per year.
How should ordinary citizens protect themselves?
1. In cases of direct exposure to radiation sources
- Distance yourself from the source of radiation.
2. In cases of exposure to radiation released in the environment
- Your actions will be different, depending on the weather. In all cases, when you come home, be sure to gargle four or five times with cold water or warm water.
1) On a sunny day
- Wear a wet mask to prevent inhaling radioactive materials in the contaminated air. If possible, use a wet gauze mask. For a paper mask, you may apply wet gauze or tissues inside the mask.
- Avoid exposure to your skin. Protect your skin by keeping it covered so that radioactive materials will not cling to your skin.
- Be sure to wear a hat or a cap.
- Cover your neck with a towel.
- Wear clothes made of finely-woven fabric, such as rain coats and wind breakers.
- Don’t dust off your clothes. If you do, you may breathe in the radioactive materials stirred up from the clothes, which can result in internal exposure.
2) On a rainy day
- Avoid getting wet in the rain. Rain may contain radiation.
- Take a shower when you come home. Thoroughly wash your hair using shampoo. If you cannot take a shower, wipe yourself with a towel.
- If your things get wet in the rain, wash them well, changing the water at least three times.
What should ordinary citizens do if they become exposed to radiation?
1. In cases of direct exposure to radiation sources
If you think you might have been exposed to a strong radiation source, go to the hospital immediately, whether or not you notice any symptoms, and undergo a test of your white blood cells. Usually this situation does not occur to the general public.
2. In cases of exposure to radiation released in the environment
For the risk of ingesting or inhaling a large amount of radioactive iodine, stable iodine agents have been prepared, by the local autonomies where nuclear power plants are located, to be prescribed to everyone, including children and pregnant women. Eating seaweed (konbu, wakame, etc.) or laver seaweed at an early time to prevent iodine deficiency is also helpful.
Major Japanese institutes on radiation medicine
– National Institute of Radiological Sciences
http://www.nirs.go.jp/ENG/index.html
– Research Institute for Radiation Medicine and Biology, Hiroshima University
http://www.rbm.hiroshima-u.ac.jp/ (in Japanese)
For more detailed information
– Website of the National Institute of Radiological Sciences located in Chiba Prefecture
http://www.nirs.go.jp/ENG/index.html
– One Day In Hiroshima – An Oral History, by Nanao Kamada, published by JPPNW (Please contact onedayhiroshima@msn.com to order the book.)
Dr. Nanao Kamada
Chairman of the Board of Directors, Hiroshima A-Bomb Survivors Relief Foundation; professor emeritus of Hiroshima University; honorary member of the Japan Radiation Research Society; and director of the Japanese Branch of the International Physicians for Prevention of Nuclear War.
Translated by Naoko Koizumi and Adam Beck
