Rain radiation falls relatively quickly over time. Most areas become quite safe to travel and decontaminate after three to five weeks. Residual radiation is defined as radiation emitted more than one minute after detonation. If the fission explosion is an aerial blast, the residual radiation will mainly come from the debris of the weapon.
If the explosion occurs on or near the surface, soil, water and other materials in the neighborhood will be absorbed upwards by the rising cloud, causing early (local) and late (global) precipitous rainfall. Early precipitation settles on the ground for the first 24 hours; it can contaminate large areas and be an extreme and immediate biological hazard. Delayed precipitated rain, which arrives after the first day, consists of microscopic particles that are dispersed by prevailing winds and are deposited in low concentrations on possible large portions of the Earth's surface. To protect yourself from contamination, it is important to remove any contaminated clothing and clean or wash any unprotected skin that was exposed after the rain hit.
Hand sanitizer does not provide protection against fallout. If possible, avoid touching your eyes, nose, and mouth. Do not use disinfectant wipes on your skin. The amount of radiation released in a nuclear explosion is measured in roentgen (R). Large doses of radiation of approximately 20 roentgen or more can produce developmental defects.
These effects would likely be limited to areas of heavy local rainfall in nuclear warring nations and would not become a global problem. A nuclear electromagnetic pulse (PEM) is the time-varying electromagnetic radiation that results from a nuclear explosion. Estimates suggest that the consequences of more than 500 megatons of nuclear tests until 1970 will produce between 2 and 25 cases of genetic diseases per million live births in the next generation. The highest levels of outdoor rain radiation occur immediately after the arrival of rain and then decrease over time. The 1963 Limited Nuclear-Test-Ban Treaty ended atmospheric testing for the United States, Great Britain and the Soviet Union, but two major non-signatories, France and China, continued nuclear testing at a rate of approximately 5 megatons per year. In conclusion, it takes three to five weeks for nuclear fallout to clear from most areas.
However, it is important to take precautions when exposed to fallout as it can cause serious health issues if not handled properly.
