Not to be confused with Ionizing radiation. Illustration of the relative abilities of three different types of ionizing radiation to penetrate solid matter. Note caveats in the text about this simplified diagram. The international symbol for properties of alpha beta and gamma rays pdf and levels of radiation that are unsafe for unshielded humans.
Radiation in general exists throughout nature, such as in light and sound. In physics, radiation is the emission or transmission of energy in the form of waves or particles through space or through a material medium.
Radiation is often categorized as either ionizing or non-ionizing depending on the energy of the radiated particles. Ionizing radiation carries more than 10 eV, which is enough to ionize atoms and molecules, and break chemical bonds.
This is an important distinction due to the large difference in harmfulness to living organisms. A common source of ionizing radiation is radioactive materials that emit α, β, or γ radiation, consisting of helium nuclei, electrons or positrons, and photons, respectively.
Other sources include X-rays from medical radiography examinations and muons, mesons, positrons, neutrons and other particles that constitute the secondary cosmic rays that are produced after primary cosmic rays interact with Earth’s atmosphere. Gamma rays, X-rays and the higher energy range of ultraviolet light constitute the ionizing part of the electromagnetic spectrum. This type of radiation only damages cells if the intensity is high enough to cause excessive heating. Ultraviolet radiation has some features of both ionizing and non-ionizing radiation.
While the part of the ultraviolet spectrum that penetrates the Earth’s atmosphere is non-ionizing, this radiation does far more damage to many molecules in biological systems than can be accounted for by heating effects, sunburn being a well-known example. These properties derive from ultraviolet’s power to alter chemical bonds, even without having quite enough energy to ionize atoms. This aspect leads to a system of measurements and physical units that are applicable to all types of radiation. The intensity of all types of radiation from a point source follows an inverse-square law in relation to the distance from its source.
Like any ideal law, the inverse-square law approximates a measured radiation intensity to the extent that the source approximates a geometric point. Some kinds of ionising radiation can be detected in a cloud chambers.