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Dr. Tsubokura's Radiation Lecture Vol.95

Author: Masaharu Tsubokura

Editors: Akihiko Ozaki M.D., Yuki Senoo

189. The daily average radiation exposure from space accounts for half of the annual radiation exposure on Earth

The previous article explained that natural radiation comes from not only radioactive substances in rocks and soil but also from outer space. This radiation reaching Earth from the universe is called cosmic rays.

Our exposure to cosmic rays is very low and unlikely to cause any adverse health effects at the ground level. This is because the atmosphere surrounding the Earth shields it from cosmic rays and provides natural protection against high energetic radiation, meaning the dose of cosmic rays increases at greater distances from the ground. The daily average dose of radiation exposure received by astronauts at the International Space Station located approximately 400 kilometers above the surface of the Earth is about one millisievert, which accounts for half of the annual natural radiation exposure we receive on the Earth.

Since cosmic rays originate from the sun, the level of radiation exposure rapidly increases to a dangerous level when a sudden explosion on the surface of the sun occurs.