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 swelling, material creep, and embrittlement. Ionizing radiation can also accelerate existing chemical reactions such as polymerization and corrosion, by contributing to the activation energy required for the reaction. Optical materials darken under the effect of ionizing radiation. High-intensity ionizing radiation in air can produce a visible ionized air glow of telltale bluish-purplish color. The glow can be observed, e.g., during criticality accidents, around mushroom clouds shortly after a nuclear explosion, or inside of a damaged nuclear reactor like during the Chernobyl disaster. Monatomic fluids, e.g. molten sodium, have no chemical bonds to break and no crystal lattice to disturb, so