Radioactivity is the process by which some chemical elements emit very energetic radiation, capable of interacting with matter. The sun is a source of natural radiation, while x-rays and the atomic bomb are sources of artificial radiation. Isotopes are atoms whose number of protons and neutrons can be stable. However, when these numbers are unstable, the isotope emits radiation until stability is reached. This infographic from the Ábaco collection is included in the Science for all series, which also includes those titled: Movement, Force, Gravity and Pressure.