Both Pauling and Russell were energized by a common concern over the growing power of the new bombs. Whether they were called "H-Bombs," "U-Bombs," or "Superbombs" -- all of which referred to the same high-yield weapons that used a Hiroshima-style atomic explosion to set off an even bigger burst from an outer coating of uranium -- they presented new risks. The new, bigger bombs, exploded in a series of tests by both the US and Russia through the latter half of the 1950s, released a riot of exotic radioactive isotopes, some never before seen on earth. The potential effects were frightening because so little was known about the health effects of low-level radiation. Public attention focused on one of the fallout components, strontium-90, a long-lived radioactive substance that was similar enough to calcium to enter the food chain, falling first on grass, then appearing in cow’s milk, then depositing in human bones -- especially those of children. Once in the bone, it decayed, exposing the tissue around it to radiation.

Pauling assumed the worst, and publicized his own estimates of health risk, extrapolating numbers from animal studies of radiation damage. Averaged over the population, he came up with a figure that each roentgen of added exposure would shorten the average life by two or three weeks. His numbers -- which predicted thousands of new cancers and cases of "premature aging" -- were vigorously denied by the Atomic Energy Commission.

Pauling remained undeterred and steadily his message broadened. By 1959 his "stump speech" had evolved into a frightening vision indeed: The United States had stockpiled enough nuclear weapons to kill everybody in the world twenty times over; all the talk of bomb shelters and civil defense was "just silly"; the AEC was a "schizophrenic" agency; "the only safe amount of strontium-90 in the bones of our children is zero."