There are three forms of radioactivity :
There is no limit to the amount of radiation below which there is no damage to living ceatures. The extraction of radioactive materials and their use for civil and military purposes incurs the cost of this damage. Radioactivity can persist for seconds or for long periods, in some cases for millions of years. The rate at which the activity declines cannot be altered.
Mining and processing of nuclear material inevitably result in the release of particles which contaminate the surroundings. Nuclear power stations discharge effluent into the sea, land and air. After use radioactive material has to be kept in isolation until the activity has reduced sufficiently for it to be placed in some permanent depository. An explosion of a nuclear plant can result in radioactive material bieng spread over a wide area. The explosion at Chernobyl in the Ukraine in 1986 caused the contamination of most of Europe. A nuclear explosion causes the release of large doses of radiation and if it takes place at ground level the soil taken into the air forms a radioactive cloud which can be carried over hundreds of miles.