The feasibility study under review did not consider all the weapons tests indicated in Table 1 but was restricted to aboveground tests during 1951–1962, so it embraces only the atmospheric weapons tests conducted by the United States, the former USSR, and the United Kingdom. The authors of the draft report offer as a rationale for that restriction the assertion that “it is generally acknowledged that the most important contributions to the radiation doses arose from atmospheric nuclear tests conducted by the United States, the United Kingdom, and the former USSR during the pre-1962 time period.” To support that statement, they note that “the tests considered in this report that were conducted at the NTS account for over 95% of the total ¹³¹I produced during the entire testing period at the NTS (NCI, 1997).”

Although the detonation of a nuclear weapon produces more than 900 fission products, only about 165 radionuclides have half-lives long enough to contribute to fallout and thus to constitute a potential threat to human health. The threat arises from exposure of a person to radioactive materials deposited on the ground, termed external or ambient exposure, and through the inhalation or ingestion of radioactive materials, called internal exposure.

External exposure to fallout from the NTS tests was evaluated in the feasibility study by estimating the deposition density of some 43 radionuclides throughout the United States and