Radiation is the collective name for electromagnetic radiation and particle radiation, both of which can be ionizing radiation. Ionizing radiation is a subatomic particle or very short electromagnetic wave which can disturb atoms in its path, causing them to loose electrons. This leaves the atoms with an electric charge. Ionizing radiation is chiefly emitted by Radioactive materials and Nuclear reactions. Radiation is also produced by chemical reactions, by hot objects and by gases excited by the flow of electric current through them.
Cells subjected to ionizing radiation may mutate or die. Because "radiation" is a very general term, and includes a wide range of phenomena quite different from each other, it should be noted that the degree to which radiation can harm living cells depends on those differences as well as on the intensity of the radiation and the length of the exposure.