Radiation sickness, also known as acute radiation syndrome or ionizing radiation injury, is illness resulting from human exposure to ionizing radiation. The radiation exposure may be from natural sources, such as radium, or from man-made sources, such as x rays, nuclear reactors, or atomic bombs. Ionizing radiation penetrates cells of the body and ultimately causes damage to critically important molecules

Radiation Sources
* includes occupation exposure, nuclear fallout, and the production of nuclear materials for nuclear power and weapons
Natural Sources
Radon gas	55%
Inside body	11%
Rocks, soil, and groundwater	8%
Cosmic rays	8%
Artificial sources
Medical x rays	11%
Nuclear medicine	4%
Consumer products	3%
Miscellaneous*	<1%

such as nucleic acids and enzymes. Immediate cell death may occur if the dose of ionizing radiation is sufficiently high; lower doses result in cell injury which may preclude cell replication. Tissues at greatest risk for radiation injury are those which have cells that are rapidly...