Dr. Tsubokura's Radiation Lecture Vol.94

Author: Masaharu Tsubokura

Editors: Akihiko Ozaki M.D., Yuki Senoo

187. Cosmic rays pour down on Earth from outer space

The impact of radiation on health is determined by the extent of radiation exposure, not by whether one received any radiation exposure. Although the Fukushima Daiichi nuclear power plant accident widely dispersed radioactive substances and caused nuclear contamination, we have always been exposed to natural radiation to some extent, even before the disaster.

It is well known that natural radiation is emitted from radioactive substances in soil and rocks. In addition to natural radiation from soil, about 100 years ago, it was discovered that natural radiation reaches the Earth from outer space as well.

Back then, scientists measured radiation dose rates at various altitudes; for example, by climbing the Eiffel Tower in Paris or using a hot-air balloon. They originally assumed that radiation exposure due to radioactive substances in the ground would lessen as they were measured further from the ground. However, the results of these experiments were contrary to this hypothesis, as the dosage increased as the measurement points moved away from the ground.