A New Calculation Explains the Mechanism Behind Carbon Dating

The new approach looks at the way the mass of mesons changes as they travel through an atomic nucleus. Mesons (particles such as pions, containing a quark and an antiquark) are thought to mediate the nuclear force between two nuclei. Radiocarbon dating began in 1949 when Willard Libby said that the amount of carbon-14 (the radioactive cousin of carbon-12) left in an object (such as a fossil tree) could provide an estimate of how old the object was.

The thinking was that the organism, while it was alive, would constantly ingest enough of the rare C-14 to replace those nuclei that were decaying into N-14 (the other products being an electron and a neutrino). But as soon as the organism died, the ratio of C-14/C-12 would begin to drop exponentially since the C-14 was no longer being replaced. Measuring the ratio in terms of radioactive half-lifes would provide a good estimate of the fossil. This method has been used by archeologists ever since to measure the age of things, at least those things that had been alive at some point during the past thousands of years.

A big questions presented itself: if the radioactive half-life of C-11 is 20 minutes, and that of O-14 is 1 minute, and that of O-15 is 2 minutes, and that of N-13 is 10 minutes, why is the life-time of C-14 some 3 billion minutes (5730 years)? This is what Jeremy Holt and his colleagues at Stony Brook, TRIUMF (the accelerator facility in Vancouver), and the University of Idaho have set out to determine. Holt says that the anomalously long C-14 half-life has been a mystery to theorists for half a century.

An earlier theory, called Brown-Rho scaling (named for Gerry Brown and Mannque Rho, advanced in 1991), suggested that the masses of most mesons decrease uniformly when (insofar as they carry the nuclear force operating inside nuclei) they travel through dense nuclear material (see figure at http://www.aip.org/png/2008/294.htm ). Holt (jeholt@tonic.physics.sunysb.edu, 631-632-9843) and his fellow authors bring things up to date by accounting, with fair accuracy, for the observed long C-14 lifetime. (Holt et al., Physical Review Letters upcoming article)