The destructive effects of nuclear explosions can extend miles from the point of detonation, and the lethal consequences can cover communities hundreds of miles downwind. This form of radioactive contamination is known as Nuclear Rain, and it represents the primary risk of exposure to ionizing radiation for a large nuclear weapon. If you find yourself in the vicinity of a nuclear detonation, you would be exposed to injuries from collapsed buildings or flying shrapnel, and most buildings within a 0.5 mile (0.8 km) radius would be knocked down or severely damaged. Even if you survive all of that, you still have to deal with radiation poisoning and other nuclear consequences.
Radioactive fallout has occurred all over the world, and people have been exposed to iodine-131 from atmospheric nuclear tests. As the nuclear energy sector continues to grow, international rhetoric around nuclear war intensifies and the ever-present threat of radioactive materials falling into the hands of dangerous people persists, many scientists are working hard to find the best way to protect humans from the harmful effects of high-energy radiation. 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. There are three very different versions of the precipitation pattern of this test, because rainfall was measured only in a small number of widely spaced Pacific atolls. Since large doses of radiation of approximately 20 roentgen or more are needed to 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.
For high-altitude nuclear explosions, these electrons are captured in the Earth's magnetic field at altitudes between twenty and forty kilometers, where they interact with the Earth's magnetic field to produce a coherent nuclear electromagnetic pulse (NEMP) that lasts approximately one millisecond. However, groundwater supplies, such as aquifers, would initially remain uncontaminated in the event of a nuclear fallout. For more information on the current state of nuclear weapons in the world, including the scale of bombs, you can visit the Nuclear Notebook in the Bulletin of Atomic Scientists.
