Carbon-14’s longevity explained

Daniel Fulton, Gennady Malyshev, Emily Peck, Corey Zehfus

Radiocarbon dating is easily among the most important developments of recent science. The method, developed soon after World War II by Willard F. Libby, takes advantage of the fact that all living things, during their life, ingest carbon and stop doing so when they die.There are three naturally occurring isotopes of carbon: C-12, C-13 and C-14. Carbon-12 and carbon-13 are stable and occur most often, with carbon-14 lagging far behind in number. The rarity of carbon-14 is a result of its radioactive decay into nitrogen-14 with a half-life of about 5,730 years. It is this property that makes the elusive carbon-14 the isotope of interest in carbon dating.

During its life, a plant or animal continuously ingests carbon, either from the atmosphere or the food it eats. Once it dies, however, whatever carbon it had within remains there, since the biological processes that would have replaced it or collected more no longer function. As time passes after the creature’s death, the carbon-14 inside it starts to break down into nitrogen. By measuring the ratio of nitrogen-14 to carbon-14, a scientist can get an accurate picture of the age of the biological material.

This technique sheds a great deal of light on several tens of thousands of years before the start of the historic record, but is limited by the 5,730-year half-life of carbon-14. Ten of these half-lives, around 50,000 years, exhaust most of the carbon-14 in biological material. Nonetheless, carbon dating is vitally important to a wide variety of sciences.

Despite the heavy use of radiocarbon dating in a number of fields, until recently, the processes involved in carbon-14 decay were not fully understood. The measured half-life of 5,730 years is unusually long for an atom with as few protons as carbon, and theoreticians in the past have had a hard time coming up with an explanation for this occurrence.

In a future issue of Physical Review Letters, Gerald Brown and Jeremy Holt of Stony Brook University in New York hope to mathematically confirm the Brown-Rho scaling theory explaining the phenomenon.

Brown-Rho scaling involves two versions of the strong nuclear force, termed the central and tensor forces, which in most isotopes are out of balance. The unbalanced nuclear forces lead directly to faster decay. In carbon-14, the theory says, the two forces are mostly balanced, leading to a much more stable nuclear configuration, and longer half life. The pending mathematical study should lend strong evidence in favor of this explanation.

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