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A radiation accident occurred in Samut Prakan Province, Thailand in January–February 2000. The accident happened when an insecurely stored unlicensed cobalt-60 radiation source was recovered by scrap metal collectors who, together with a scrapyard worker, subsequently dismantled the container, unknowingly exposing themselves and others nearby to ionizing radiation. Over the following weeks, those exposed developed symptoms of radiation sickness and eventually sought medical attention. The Office of Atomic Energy for Peace (OAEP), Thailand's nuclear regulatory agency, was notified when doctors came to suspect radiation injury, some seventeen days after the initial exposure. The OAEP sent an emergency response team to locate and contain the radiation source, which was estimated to have an activity of , and was eventually traced to its owner. Investigations found failure to ensure secure storage of the radiation source to be the root cause of the accident, which resulted in ten people being hospitalized for radiation injury, three of whom died, as well as the potentially significant exposure of 1,872 people. ==Background== Cobalt-60 (60Co) is a synthetic radioactive isotope of cobalt, with a half-life of 5.27 years, and emits highly penetrating gamma rays. It is commonly used as a radiation source for radiotherapy and equipment sterilization in the hospital setting, and has several other industrial uses as well. The device involved in the Samut Prakan accident was a rotational Gammatron-3 teletherapy unit,〔 (Siemens ads with a picture of a Gammatron-3 unit)〕 manufactured by Siemens and imported to Thailand in 1969. It was licensed for and installed at Ramathibodi Hospital in Bangkok;〔 the radiation source involved was a replacement installed in 1981, with an initial radioactive activity of .〔IAEA 2002, pp. 1, 5, 7.〕 At the time of the accident in 2000, its activity was estimated to have decayed to . The licensing of radioisotopes and nuclear material for import, export, possession and use in Thailand is regulated by the Thai Atomic Energy Commission for Peace and its working body, the Office of Atoms for Peace (OAP), formerly known as the Office of Atomic Energy for Peace (OAEP). In principle, the licensing process would involve annual safety inspections, but due to lack of personnel and resources, such inspections were not always properly done, nor were regulatory and control protocols strictly enforced.〔IAEA 2002, pp. 3–4.〕 The hospital retired the radiotherapy unit in 1994 and acquired a new one from Nordion via its Thai agent Kamol Sukosol Electric Company (KSE).〔IAEA 2002, p. 5 〕〔 The old unit and its 60Co source could not be returned either to its original German manufacturer Siemens, which had stopped producing or servicing them, or to the Canadian supplier Nordion, which was not the original manufacturer. Consequently, the hospital sold the old unit to KSE, which already had another licensed unit in storage. However, neither the hospital nor KSE informed the OAEP of the transfer. In 1996 an OAEP inspection found that KSE had three unlicensed units in its warehouse, which had been licensed for the storage of a single unit in 1988.〔IAEA 2002, pp. 6–7.〕 KSE's lease of the warehouse was terminated in 1999. KSE subsequently returned the licensed unit, while moving the three unregistered units to an unused car park in Bangkok's Prawet District, which was owned by its parent company. The car park was fenced, but the fence had been breached and nearby residents regularly entered to play football in its empty areas. KSE notified the OAEP of its transfer of the licensed unit, but did not mention the other three, which remained orphan sources.〔 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「Samut Prakan radiation accident」の詳細全文を読む スポンサード リンク
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