This book aims to explain radiation from a somewhat different aspect than its traditional image as something that is scary, dangerous, hazardous, and so on, to produce the correct understanding that radiation is carrying energy, and to convince readers that radiation is not "scary" but controllable and useful. As for radiation itself, many introductions or textbooks have been published, as in radiochemistry, radiobiology, and radiology. In most of them, the biological effects of radiation exposure are the main subjects, which often enhance the feeling that radiation is dangerous, and the...