A nuclear explosion is energy being released from a very fast nuclear reaction. It can be caused by nuclear fission, nuclear fusion, or both.
Atmospheric nuclear explosions are associated with mushroom clouds, although mushroom clouds can occur as a result of large chemical explosions. It is also possible to have an air-burst nuclear explosion without these clouds. Nuclear explosions produce radiation and radioactive debris.
The nuclear weapon was first detonated on 6 August 1945, when the United States dropped a uranium gun-type device on the Japanese city of Hiroshima. The second event occurred three days later when United States dropped a plutonium implosion-type device on the city of Nagasaki. These bombings resulted in the immediate deaths of around 120,000 people while more died over time due the nuclear radiation.
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