In 1959, the AEC and the nuclear power establishment made a momentous policy change. They abandoned the concept of a tolerance dose rate below which harm is undetectable, and adopted the Linear No Threshold hypothesis, which claims that harm is proportional to cumulative dose, regardless of how rapidly or how slowly that dose is received. In other words, radiation harm is unrepairable. It just builds up. The tolerance dose rate model assumes our bodies can repair radiation damage. As a result, harm does not build up as long as we stay below the tolerance dose rate, which up to 1950 was 1 mSv/d.

What's really perplexing about this foundational transformation is that it apparently was done with no discussion. There seems to be no official decision from the AEC. No meeting minutes. No dueling memos. The official history of the AEC, Mazuzan and Walker, 511 tedious pages covering the period 1946-1962, makes no mention of the decision.1
The book makes no mention of LNT at all.