Ionizing radiation 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. The International Commission on Radiological Protection manages the International System of Radiological Protection, which sets recommended limits for dose uptake. Background radiation comes from both natural and man-made sources. The global average exposure of humans to ionizing radiation is about 3 mSv (0.3 rem) per year, 80% of which comes from nature. The remaining 20% results from exposure to man-made radiation sources, primarily
Ionizing radiation LET occurs and neutrons, alpha particles, low-energy protons, and other nuclei will be released by the collisions and contribute to the total absorbed dose of tissue.<ref name="NASA/TP-1999-209320"> Kim, Myung-Hee Y.; Wilson, John W.; Cucinotta, Francis A.; Simonsen, Lisa C.; Atwell, William; Badavi, Francis F.; Miller, Jack, NASA Johnson Space Center; Langley Research Center, May 1999.</ref> Indirect ionizing radiation is electrically neutral and therefore does not interact strongly with matter. The bulk of the ionization effects are due to secondary ionizations. An example of indirectly ionizing radiation is neutron radiation. Even though photons are electrically neutral, they can ionize atoms directly