Radioactivity is a phenomenon that occurs when certain types of matter emit energy or particles in the form of radiation. This radiation can cause cancer, serious environmental damage, or be used to create useful technologies. There are different levels of radioactivity and the amount of exposure to it can determine the amount of damage it can cause. At the core of radioactivity is the atom.
All matter is made up of chemical elements, and these elements are composed of atoms. While atoms remain unchanged over time, radioactive atoms are different in that they naturally emit small particles and energy. The particles and energy released from these atoms is known as radiation. If an element or isotope of that element is said to be radioactive, it means that it emits some kind of radiation.