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|
|Natural Sources||Normal occurrences||Cosmic radiation|
|Enhanced sources||Metal mining and smelting|
|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 sources||Peaceful purposes||Nuclear power production|
|Transport of nuclear and radioactive material|
|Application other than nuclear power|
|Military purposes||Nuclear tests|
|Residues in the environment. Nuclear fallout|
|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 sources||Peaceful purposes||Nuclear power industries|
|Medical uses of radiation|
|Industrial uses of radiation|
|Military purposes||Other 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.
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 radiation||Examples|
|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.|
Some images of ionizing radiation sources