Linear no-threshold model

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 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.

There are three active (2016) challenges to the LNT model currently being considered by the US Nuclear Regulatory Commission. One was filed by Nuclear Medicine Professor Carol Marcus of UCLA, who calls the LNT model scientific "baloney".

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 it estimates a positive number of excess deaths at levels that would have had zero deaths, or saved lives, in the two other models. Such practice has been condemned by the International Commission on Radiological Protection.

...
Wikipedia