The Effects of Carbon-14

As most regular readers of this blog know by now, Linus Pauling’s efforts on behalf of peace began in earnest in 1945, after the United States exploded two atomic bombs over Japan.  Appalled by the wanton destructiveness of these acts and alarmed by the future implications of nuclear weapons, Pauling began giving a great number of speeches on the atomic bomb, and before long his talks had become extremely popular.

Pauling continued delivering these speeches for a number of years, until it appeared that his career in activism might wind down due to the great time demands required by his ambitious program of protein research. However, after the US detonated the first hydrogen bomb in 1954 and the term “fallout” started to become more commonplace, Pauling’s vigor as an activist returned. Because of its inherently chemical nature, Pauling quickly became somewhat of a fallout expert, and in 1958 he wrote a paper about the dangers of carbon-14, a topic that had not been discussed at great length.

Carbon-14 is a radioactive isotope of carbon that is not prevalent in nature – it comprises roughly one part per trillion of all the carbon in the atmosphere – but is a byproduct of nuclear explosions. Pauling’s paper on the subject, titled “Genetic and Somatic Effects of Carbon-14,” was based on carbon-14 data acquired by Willard Libby, a chemist who won the 1960 Nobel Prize in Chemistry for developing the radiocarbon dating technique, which measures the radioactive decay of carbon-14 in organic materials.

Libby estimated that, by 1958, roughly 232 kilograms of carbon-14 had already been released due to bomb testing. Of these 232 kg, Pauling speculated that about one-third had been incorporated into the atmosphere, and that the other two-thirds had fallen back to the Earth in the form of calcium carbonate.

The real threat of carbon-14, Pauling felt, is a result of its long half-life. Although it may not present a significant short-term effect, radioactive carbon that is incorporated into the body will remain there and emit radiation for as long as the organism exists, thus increasing the possibility of health problems both for the affected body as well as its offspring.

From Libby’s data, Pauling determined that at the rate that bombs were being tested circa 1958 – which Pauling calculated to be 30 megatons worth of explosions – 74 kg of carbon-14 were released per year. Based on these numbers as well as estimates for radiation dosages published by James F. Crow, a member of the joint NAS-NRC Committee on Genetic Effects of Atomic Radiation, Pauling determined that one’s exposure to carbon-14 over the entire lifetime of the isotope is actually four times higher than what had normally been assumed for worldwide fallout.

Using this information, Pauling calculated that, at 1958 population levels, one year of bomb testing would therefore produce enough carbon-14 to lead to “12,000 children with gross physical or mental defect, 38,000 stillbirths and childhood deaths, and 90,000 embryonic and neonatal deaths.”

Although these numbers are very small when compared to the total 1958 world population of just under three billion, they still are suggestive of a significantly dangerous side-effect from nuclear weapons testing. Furthermore, Pauling accounted for the fact that, as the population continued to grow, the number of people exposed to carbon-14 would also increase. He estimated that population growth would rise until it leveled off at a point where the number of births per year were five times that of the 1958 value. At this population, Pauling calculated the effects of carbon-14 from one year worth of bomb-testing to be 55,000 children with gross physical and mental defect, 170,000 stillbirths and childhood deaths, and 425,000 embryonic and neonatal deaths.

Notes re: estimates of carbon-14 following nuclear detonation. October 9, 1959.

Pauling concluded his paper by reiterating that, because of its long half-life, carbon-14 has a negligible effect on the generation that immediately follows a period of bomb-testing, and that the real threat was to future generations. Finally, he also confessed to the large amount of uncertainty in the calculations given throughout the paper, warning that his numbers could be as much as five times too high or five times too low.

Clearly Pauling was very concerned about carbon-14 fallout, but this worry wasn’t shared by a majority of his peers. Nonetheless, later attempts to find fault with his calculations proved inconclusive, and Pauling’s argument that carbon-14 added significantly to the dangers of radioactive fallout remained an important contribution to the continuing debate over nuclear weapons tests.