Sources of radiation

Ionizing radiation is generated through nuclear reactions, nuclear decay, by very high temperature, or via acceleration of charged particles in electromagnetic fields. Natural sources include the sun, lightning and supernova explosions. Artificial sources include nuclear reactors, particle accelerators, and x-ray tubes.

The United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) itemized types of human exposures.

Type of radiation exposures
Public exposure
Natural SourcesNormal occurrencesCosmic radiation
  Terrestrial radiation
 Enhanced sourcesMetal mining and smelting
  Phosphate industry
  Coal mining and power production from coal
  Oil and gas drilling
  Rare earth and titanium dioxide industries
  Zirconium and ceramics industries
  Application of radium and thorium
  Other exposure situations
Man-made sourcesPeaceful purposesNuclear power production
  Transport of nuclear and radioactive material
  Application other than nuclear power
 Military purposesNuclear tests
  Residues in the environment. Nuclear fallout
Historical situations
Exposure from accidents
Occupational radiation exposure
Natural Sources Cosmic ray exposures of aircrew and space crew
  Exposures in extractive and processing industries
  Gas and oil extraction industries
  Radon exposure in workplaces other than mines
Man-made sourcesPeaceful purposesNuclear power industries
  Medical uses of radiation
  Industrial uses of radiation
  Miscellaneous uses
 Military purposesOther exposed workers
Source UNSCEAR 2008 Annex B retrieved 2011-7-4

The International Commission on Radiological Protection manages the International System of Radiological Protection, which sets recommended limits for dose uptake.

Ionizing radiation – Wikipedia

What are the Types of Ionizing Radiation?

Five types of ionizing radiation—alpha particles, beta particles, positrons, gamma rays, and X-rays—are the primary focus of this Ionizing Radiation Safety and Health Topics page.

This page also introduces another type of ionizing radiation, neutron particles, although significant worker doses from neutrons are most likely near reactors or when using neutron sources (e.g., californium (Cf)-252, americium (Am)-241/beryllium (Be), plutonium (Pu) Be). Worker doses from neutrons could also occur in certain radiological emergencies. Visit OSHA’s Radiation Emergency Preparedness and Response page for more information on protecting workers during radiological emergencies.

Type of ionizing radiationExamples
PARTICULATE RADIATION (sub-atomic particles with mass, such as alpha and beta particles, electrons, and neutrons)
Alpha particles (α)Positively charged particles consisting of two protons and two neutrons emitted from the nucleus of some radioactive atoms. An alpha particle is the nucleus of a helium atom.Unstable atoms with a low neutron-to-proton ratio may emit alpha particles.Radionuclides that emit alpha particles include:Uranium-238 (U-238), U-234, U-235Radium-226 (Ra-226), Ra-223, Ra-224, (decay products of uranium)Radon-222 (Rn-222), Rn-219, Rn-220 (decay products of radium)Thorium-230 (Th-230), Th-227, Th-228Americium-241 (Am-241)Polonium-210 (Po-210)For example, a Po-210 atom has 84 protons and 126 neutrons, and is unstable (i.e., radioactive). To become more stable, the Po-210 atom ejects an alpha particle, consisting of two protons and two neutrons. Having lost two protons and two neutrons, the radioactive Po-210 atom becomes stable lead-206 (Pb-206), with 82 protons and 124 neutrons.
Beta particles (β-) and Positrons (β+)Beta particles (β-)Negatively-charged, fast-moving electrons emitted from the nucleus of various radionuclides. Unstable atoms with a high neutron-to-proton ratio emit negatively-charged beta particles.Positrons (β+)Positively-charged, fast-moving electrons emitted from the nucleus of certain radionuclides. Unstable atoms with a low neutron-to-proton ratio can emit positrons.Beta particles (β-)Some radionuclides that emit beta particles include:Strontium-90 (Sr-90)Phosphorus-32 (P-32)Carbon-14 (C-14)For example, a carbon-14 atom has six protons and eight neutrons, and is unstable (i.e., radioactive). To become more stable, the C-14 atom releases radiation by turning a neutron into a proton and ejecting an electron (i.e., a beta particle). Having gained a proton and lost a neutron, the radioactive C-14 atom becomes stable nitrogen-14 (N-14), with seven protons and 7 neutrons.Positrons (β+)Fluorine-18 (F-18) is an example of a positron-emitting radionuclide that is commonly used in medical facilities for positron emission tomography (PET) scanning.An F-18 atom has nine protons and nine neutrons, and is unstable (i.e., radioactive). To become more stable, the F-18 atom releases radiation by turning a proton into a neutron and ejecting a positron. Having gained a neutron and lost a proton, the radioactive F-18 atom becomes stable oxygen-18 (O-18), with eight protons and 10 neutrons.
Neutron particlesNeutral (i.e., having no electric charge) particles that can be emitted from the nuclei of various unstable radionuclides. Neutrons are high-speed nuclear particles that are the only type of ionizing radiation that can make objects radioactive.Nuclear fission and fusion reactions, as well as neutron sources (e.g., Cf-252, AmBe), neutron generators, and some particle accelerators, produce neutrons. For example, neutrons would be produced from the detonation of a fissile nuclear weapon, such as an improvised nuclear device (IND). Visit OSHA’s Radiation Emergency Preparedness and Response page for more information.
ELECTROMAGNETIC RADIATION (Gamma rays and X-rays) has no mass and no charge.
Gamma rays (γ)High-energy electromagnetic photons emitted from the nucleus of an unstable, excited atom. Gamma rays are pure energy and can travel great distances at high speed.Some radionuclides that emit gamma rays include:Iodine-131 (I-131)Cesium-137 (Cs-137)Cobalt-60 (Co-60), cobalt-57 (Co-57)Gallium-67 (G-67)Technetium-99m (Tc-99m)Iridium-192 (Ir-192)Gamma rays are often emitted along with alpha or beta particles during radioactive decay (e.g., Co-60, Ir-192).
X-raysHigh-energy electromagnetic photons emitted from outside the nucleus. The primary difference between X-rays and gamma rays is that X-rays are emitted from processes outside the nucleus, but gamma rays originate inside the nucleus.Some radionuclides that emit X-rays include:Iodine-125 (I-125)Iron-55 (Fe-55)Machines containing an X-ray tube also electronically produce X-rays.
Ionizing Radiation – Background | Occupational Safety and Health Administration (

Some images of ionizing radiation sources

“Atom Bomb Nuclear Explosion” by Burnt Pineapple Productions is marked under CC0 1.0. To view the terms, visit
“Nuclear Explosion, Chicago [1902×1080] – art0on” by Douglas Tofoli is marked under CC PDM 1.0. To view the terms, visit
“Japan Apocalypse _DDC3497” by Abode of Chaos is licensed with CC BY 2.0. To view a copy of this license, visit

– Japan Apocalypse _DDC3778.jpg” by Abode of Chaos is licensed with CC BY 2.0. To view a copy of this license, visit
“Trash in the surf, Poison in the Sea” by boellstiftung is licensed with CC BY 2.0. To view a copy of this license, visit