Abstract
The Linear No-Threshold (LNT) model has been the basis of radiation regulatory policy for more than 70 years but, lacking valid scientific foundation, remains only an assumption. The LNT extrapolation from observed high-dose effects to putative low-dose responses entails that all ionizing radiation exposure down to zero is harmful proportionally to dose; this implicitly denies the existence of a protective biological response to the observed initial radiation-induced damage. Denying such a response, LNT further implies that the harm is cumulative throughout life, regardless of how low the dose or dose rate. But there are evolved protective biological responses that quickly repair or remove any radiogenic damage from low doses and dose rates, thereby preventing damage from accumulating. LNT and its offspring, ALARA (as low as reasonably achievable), do not err on the side of caution and are not conservative. Instead the public needs protection from radiophobia rather than from low-dose/rate radiation exposure. The NRC and other regulatory agencies should no longer base their radiation protection standards on LNT. Instead regulatory policy should be based on a linear (down to a) threshold (LT) model.