SECTION III. GENERAL EVALUATIONS The decision to conduct nuclear weapons tests for the defense of our country was made at the highest level of our Government. The Atomic Energy Commission was charged with the responsibility for carrying out this decision. The AEC sought and followed the best advice both from within and outside the Government in the conduct of new and potentially hazardous operations. The record, as summarized above, must speak for itself as to potential risks incurred to the public in the fulfillment of a mission essential to national security. Of all the health aspects of nuclear weapons testing, that of radiation exposure has received the greatest attention. If, as the data and their evaluation given above indicate, there has been a relatively low degree of risk associated with past atmospheric tests (except for the fallout on the Marshallese), then why has there been so much concern expressed? There are probably several reasons. Firstly, whereas the potential radiation exposures are only a very small fraction of those received from natural background sources, they are, of course, additional amounts. Secondly, in the absence of positive proof otherwise the prudent assumption is accepted that for every little increment of radiation exposure there is a corresponding increment of biological effect ("linear" concept) - rather than the "threshold" concept where a certain total radiation dose must be received before irreparable damage occurs. 39. ae