Radiation Dose Units Radiological Information Radioactivity is a broad term that refers to changes in the nuclei of atoms that release radiation. The radiation is an energetic ray or energetic particle. For ionizing radiation, the ray or particle has enough energy to cause changes in the chemical structure of the materials it strikes. These chemical structure changes are the mechanisms by which radiation can cause biological damage to humans. This means that a human body cell may be damaged if it comes into contact with the energy from a particle or ray released by radioactive decay.
Radiation comes from many sources, some natural and some human-made.
People have always been exposed to natural or background radiation. Natural sources of radiation include the sun, and radioactive materials present in the earth's crust, building materials, and in the air, food, and water. Some sources of ionizing radiation have been created by people for various uses or as byproducts of these activities. These sources include nuclear power generation, medical diagnosis and treatment, and nuclear materials related to nuclear weapons. Radioactive waste can be harmful and thus requires isolation for up to hundreds or even thousands of years.