|
The linear no-threshold model (LNT) is a model used in radiation protection to quantify radiation exposure and set regulatory limits. It assumes that the long term, biological damage caused by ionizing radiation (essentially the cancer risk) is directly proportional to the dose. This allows the summation by dosimeters of all radiation exposure, without taking into consideration dose levels or dose rates.〔"In the absence of more conclusive data, scientists have assumed that even the smallest radiation exposure carries a risk." (GAO study )〕 In other words, radiation is always considered harmful with no safety threshold, and the sum of several very small exposures are considered to have the same effect as one larger exposure (response linearity). One of the organizations for establishing recommendations on radiation protection guidelines internationally, the UNSCEAR, has recommended in 2014 policies that do not agree with the Linear No-Threshold model at exposure levels below background levels of radiation to the UN General Assembly from the Fifty-Ninth Session of the Committee. Its recommendation states that "the Scientific Committee does not recommend multiplying very low doses by large numbers of individuals to estimate numbers of radiation-induced health effects within a population exposed to incremental doses at levels equivalent to or lower than natural background levels." This is a reversal from previous recommendations by the same organization.〔() UNSCEAR Fifty-Ninth Session 21–25 May 2012 | Published 14 August 2012〕 Whether the model describes the reality for small-dose exposures is disputed. It opposes two competing schools of thought: the threshold model, which assumes that very small exposures are harmless, and the radiation hormesis model, which claims that radiation at very small doses can be beneficial. Because the current data are inconclusive, scientists disagree on which model should be used. Pending any definitive answer to these questions and the precautionary principle, the model is sometimes used to quantify the cancerous effect of collective doses of low-level radioactive contaminations, even though such practice has been condemned by the International Commission on Radiological Protection.〔(ICRP publication 103 ), §66〕 The LNT model is sometimes applied to other cancer hazards such as polychlorinated biphenyls in drinking water.〔( ''Consumer Factsheet on: polychlorinated biphenyls'' ) US Environment Protection Agency.〕 ==History== The linear-no-threshold model was first expressed by John Gofman, and rejected by the Department of Energy, according to Gofman, because it was "inconvenient".〔(Gofman on the health effects of radiation: "There is no safe threshold" ). Ratical.org. Retrieved on 5 May 2012.〕 The National Academy of Sciences (NAS) Biological Effects of Ionizing Radiation (BEIR) report, NAS BEIR VII was an expert panel who reviewed available peer reviewed literature and writes, "the committee concludes that the preponderance of information indicates that there will be some risk, even at low doses".〔(NAS BEIR VII Phase 2 Executive Summary ) retrieved 8 October 2008〕 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「Linear no-threshold model」の詳細全文を読む スポンサード リンク
|