Becquerel (Bq): A unit that expresses the degree of a material’s ability to emit radiation (=radioactivity).
Sievert (Sv): A unit that expresses the magnitude of the effect if a person is exposed to radiation.
1 becquerel is defined as the activity of an amount of a material in which one atomic nucleus decays every second. There are various types of radiation, including alpha rays, beta rays and gamma rays, and even at the same level of becquerels, these types of radiation all have different effects on the human body.
Because of this, becquerel figures alone do not tell us what effect radiation will have on our bodies. The sievert was therefore created as a unit of the degree of radiation’s effect on the human body with consideration of the type and intensity of the radiation.- CHUBU Electric Power
- 1 rem (roentgen equivalent in man) = 0.01 sievert = 10 mSv (millisievert) = 10,000 μSv (microsievert)
Artificial background radiation in millisievert (mSv) per year:
- World: 0.61  = 0.061 rem
- USA: 3.14  = 0.314 rem
- Japan: 2.33  = 0.233 rem
- Belgium (EU): 2.78  = 0.278 rem
Natural background radiation in millisievert (mSv) per year (up to 10-20 mSv = 1-2 rem):
- World: 2.4 = 0.240 rem
- USA: 3.1o = 0.310 rem
- Japan: 1.50 = 0.150 rem
- Belgium (EU): 2.74 = 0.274 rem
Combined background radiation in millisievert (mSv) per year:
- World: 3.01 = 0.301 rem
- USA: 6.24 = 0.624 rem
- Japan: 3.83 = 0.383 rem
- Belgium (EU): 5.52 = 0.552 rem
Radioactive Materials Released into the Atmosphere at Fukushima, Japan, between March 12 and 15, 2011
- 770,000 terabecquerel (iodine equivalent)
The total amount of radiation released by the Chernobyl accident was 5.2 million terabecquerel.
Since March 2012, the radiation figures have returned to pre-accident levels in all but areas around the Fukushima Daiichi complex and certain other areas, and almost no radiation is detected in the atmosphere.
Environmental radiation readings currently being recorded in various areas are thought to be the effect of radioactive materials with long half-lives (predominantly cesium) having been deposited on the ground, etc.
A range from 1 to 20 millisieverts represents an appropriate limit for annual exposure for residents in the vicinity of a nuclear accident. – CHUBU Electric Power