Small doses of radiation are safe and the risks from atmospheric nuclear tests are negligible.

On November 1, 1952, the United States detonated its first thermonuclear weapon at Enewetak Atoll in the Pacific Ocean. The yield was 10.4 megatons,several hundred times larger than the Hiroshima bomb, larger than any previous nuclear test by an enormous margin. The fireball incinerated the island of Elugelab. The Atomic Energy Commission issued a press statement afterward describing the test as an exploration of "the practical and theoretical aspects of thermonuclear reactions." The health consequences of the fallout were not mentioned.

The AEC's approach to public communication about radiation risks in the early 1950s was shaped by two competing pressures: genuine uncertainty about low-dose health effects and an institutional determination to prevent the kind of public alarm that might complicate the test program. The agency's public statements routinely described fallout from nuclear tests as a negligible hazard to American civilians. Officials compared the radiation exposure from a nuclear test to a chest X-ray, or to the natural background radiation encountered by people living at high altitude. The comparisons were technically defensible in some narrow sense and deeply misleading in others.

What the comparisons omitted was strontium-90. This radioactive isotope, produced in large quantities by nuclear fission, behaved in the environment like calcium and was absorbed into human bones and teeth, where it continued to emit radiation for decades. Unlike external radiation sources, strontium-90 was internal: once incorporated into the skeleton, it irradiated surrounding tissue continuously. Children, whose bones were growing rapidly and whose calcium uptake was highest, accumulated the most strontium-90. Baby teeth became a measure of the problem. The Committee on Nuclear Information in St. Louis, organized by Barry Commoner beginning in 1958, collected hundreds of thousands of baby teeth from children across the country and measured their strontium-90 content. The teeth of children born in 1963, at the peak of atmospheric testing, contained roughly fifty times more strontium-90 than those of children born a decade earlier.

Linus Pauling had arrived at similar conclusions through chemistry. The 1954 Nobel laureate in chemistry, Pauling calculated in 1957 that the nuclear tests conducted to date would eventually cause thousands of additional cancer deaths annually from the resulting fallout. He circulated a petition to end nuclear testing, gathering signatures from more than nine thousand scientists in forty-nine countries. The Eisenhower administration dismissed the petition as scientifically irresponsible and politically motivated. The AEC countered Pauling's figures with its own, arguing that any increase in cancer rates would be too small to measure against baseline variation.

The question of what constitutes a safe dose of ionizing radiation was formally addressed by the National Academy of Sciences beginning in 1956, when the first Biological Effects of Ionizing Radiation report concluded that there was no threshold below which radiation could be presumed safe. The linear no-threshold model,which holds that any dose of radiation, however small, carries a proportional cancer risk,was not universally accepted but was supported by the available biological evidence. It contradicted the AEC's public messaging at every point.

The Partial Nuclear Test Ban Treaty, signed in August 1963, moved weapons testing underground and out of the atmosphere. Strontium-90 levels in baby teeth began to fall within years of the treaty's implementation. The treaty's passage owed something to the accumulating scientific evidence and considerably more to Pauling's petition and the public pressure it had helped generate,pressure built on the demonstration that the reassurances about small doses were not reassurances at all.