Wikipedia – The Chernobyl disaster triggered the release of substantial amounts of radiation into the atmosphere in the form of both particle and gaseous radioisotopes, and is the most significant unintentional release of radiation into the environment to date. It has been suggested that the Chernobyl disaster released as much as 400 times the radioactive contamination of the Atomic bombings of Hiroshima and Nagasaki. However, the work of the Scientific Committee on Problems of the Environment (SCOPE) suggests that the two events cannot be simply compared with a number suggesting that one was x times larger than the other; the isotopes released at Chernobyl tended to be longer-lived than those released by a bomb detonation, producing radioactivity curves that vary in shape as well as size.
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