The quest for nuclear energy began with the discovery of radioactivity at the end of the 19th century. Numerous experiments with materials emitting invisible rays led to a better understanding of the makeup of the atom. Ionizing radiation is a natural part of our environment. Its origin lies in the radioactive elements contained in the Earth’s crust, air, plants, and every living organism. Everyone is exposed to a certain amount of radiation from all of these sources. This is the natural background radiation. An additional dose is received from cosmic radiation and during various diagnostic and medical procedures. Nevertheless, the human organism is able to tolerate the effects of this natural dose of ionizing radiation.