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The Goiânia accident was a radioactive contamination accident that occurred on September 13, 1987, at Goiânia, in the Brazilian state of Goiás, after an old radiotherapy source was stolen from an abandoned hospital site in the city. It was subsequently handled by many people, resulting in four deaths. About 112,000 people were examined for radioactive contamination and 249 were found to have significant levels of radioactive material in or on their bodies. In the cleanup operation, topsoil had to be removed from several sites, and several houses were demolished. All the objects from within those houses were removed and examined. ''Time'' magazine has identified the accident as one of the world's "worst nuclear disasters" and the International Atomic Energy Agency called it "one of the world's worst radiological incidents".〔(The Worst Nuclear Disasters )〕 == Description of the source == The radiation source in the Goiânia accident was a small capsule containing about of highly radioactive caesium chloride (a caesium salt made with a radioisotope, caesium-137) encased in a shielding canister made of lead and steel. The source was positioned in a container of the wheel type, where the wheel turns inside the casing to move the source between the storage and irradiation positions.〔 The activity of the source was 74 terabecquerels (TBq) in 1971. The International Atomic Energy Agency (IAEA) describes the container – 51 millimeters (2 inches) in diameter and 48 mm (1.8 inches) long – as an "international standard capsule". The specific activity of the active solid was about 814 TBq·kg−1 of caesium-137 (half life of 30 years). The dose rate at one meter from the source was 4.56 gray per hour (456 rad·hr−1). While the serial number of the device was unknown, thus hindering definitive identification, the device was thought to have been made in the United States at Oak Ridge National Laboratory and was used as a radiation source for radiation therapy at the Goiânia hospital.〔 The IAEA states that the source contained when it was taken and that about 44 TBq (1200 Ci, 87%) of contamination had been recovered during the cleanup operation. This means that remained in the environment; it will have decayed to about by 2012. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Goiânia accident」の詳細全文を読む スポンサード リンク
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