Beyond the Threshold: The Regulatory Origins of the Linear Non-Threshold (LNT) Model for Radiation Protection

The Atomic Energy Act of 1946 gave the newly formed Atomic Energy Commission (AEC) a dual mandate of promoting nuclear development while regulating its safety. This paper examines the history of radiation protection during the AEC’s formative years through the lens of Alvin Weinberg’s concept of "trans-science"—questions that can be asked of science but not answered by science alone. Specifically, I argue that the Linear Non-Threshold (LNT) model emerged not merely as a biological proposition, but as a functional administrative tool responding to changing demographic assumptions and monitoring conditions.

We typically assume that dose limits are logically derived from scientific propositions regarding the dose-response relationship. However, deliberations within the radiation protection community reveal the opposite: the LNT model was a derivative of regulatory necessities. Faced with ambiguous data regarding mutation frequency, lifespan, and leukemia, the community prioritized demographic concerns. As the "at-risk" population expanded from medical professionals to the general public, advisors suggested metrics like the “doubling dose” and natural baselines to address the theoretical possibility of linearity in a regulatorily feasible manner.

This demographic shift also rendered the bureaucracy of monitoring increasingly untenable. To simplify recordkeeping, the daily unit of exposure was gradually extended to weekly, quarterly, and eventually annual limits. This shift relied on the assumption that exposure rates would remain constant in atomic facilities—an administrative convenience that acknowledged, but bypassed, the question of linearity. Thus, the LNT model was a product of the mutual construction of science and regulation, designed to operationalize the AEC’s dual mandate in an era where science reached its empirical limits.