R. Scott Kemp, teaching MIT's course 22.04 Social Problems of Nuclear Energy, devotes this lecture to the Linear No-Threshold (LNT) theory of radiation dose-response. He lays out why regulators adopted the assumption that any dose of radiation, however small, carries a proportional risk of harm, with no safe threshold below which exposure is harmless. The lecture traces the scientific and political reasoning behind this model, how it shapes radiation protection standards, and the controversies among scientists over whether the linear assumption overstates or understates real risk at low doses. Running seventy four minutes, the talk uses dose-response curves and historical regulatory decisions to show how a contested scientific model became the basis for nuclear safety policy. It is part of MIT OpenCourseWare's Fall 2025 offering of 22.04, aimed at students examining the social and political dimensions of nuclear energy.