Radiation

Radiation is a gameplay mechanic and story element throughout the Fallout series.

Background
Described as tasteless and odorless, radiation or the "phantom death" is a lingering danger present in the environment caused by the detonation of nuclear missiles and toxic waste. Measured in units known as "rads" or "sieverts," sensors outside of Vaults monitors for changes in the radiation levels as a prerequisite for entry or exit and the results of sensors placed inside are announced to inhabitants.

Comprised of Gamma rays, living creatures that absorb too much of these ionizing rays may experience blood pooling in the gums, nausea, vomiting, anemia, diarrhea, and fatigue. Symptoms may also include loss of hair, teeth, and skin. In serious cases of radiation sickness and poisoning, living creatures will suffer from gastrointestinal bleeding, violent hemorrhaging, and death, but some life forms have adapted to the radiation in the environment.

Medical treatment to alleviate damage by radiation includes care provided by Auto-Doc, Sympto-matic, makeshift archways, inoculations, decontamination arches, and system flushes. Radiation levels are measured with Geiger counters built into Pip-Boys as well as Wattz Electronics C-Radz Geiger counters. Radiation suits are utilized to mitigate the effects of exposure, with varying efficacy.

Radiation also affects weather systems, producing radstorms. These storms are weather phenomena that occur throughout the Commonwealth and in Appalachia. Radstorms result in green overcast skies and audible winds. Over the course of the storm, lightning periodically flashes and causes a brief spike of radiation in the area, inflicting 5 rads per lightning flash. Radstorms are capable of producing vortexes that are strong enough to lift people off the ground.

Centuries after the Great War, some areas such as the Glow and the Glowing Sea, are still highly irradiated. Radioactive hotspots appear near places that were struck directly by nuclear weapons, and regions varied in how long radiation persisted, ranging from clearing shortly after the war to remaining hundreds of years later. Some groups have developed religious followings revolving around radiation, such as the Children of Atom.

Mutations
Exposure to background radiation can also lead to mutations at a genetic level. It can also lead to sterility. Radiation also causes mutations in creatures, leading to the emergence of large versions of pre-War species such as radscorpions, geckos, spore plants, and brahmin. Radiation can also cause some humans to turn into ghouls or feral ghouls, immune to the negative effects of radiation. Some emit radiation and have no body heat.

Appearances
Radiation appears in all Fallout games.

Behind the scenes
According to Wikipedia, radiation in-game is greatly intensified when compared to the real world, as a fatal dose amounts to several tens of thousands of rads.