The researchers wanted to find out if they could identify a person's year of birth or year of death using precise measurements of carbon-14 levels in different post-mortem tissues.
They measured carbon-14 levels in various tissues from 36 humans whose birth and death dates were known.
The researchers found that if they assumed tooth enamel radiocarbon content to be determined by the atmospheric level at the time the tooth was formed, then they could deduce the year of birth.
C14 is continually being created and decaying, leading to an equilibrium state in the atmosphere.
When the carbon dioxide, containing C14 as well as stable C12 and C13, is taken in by plants it is no longer exposed to the intense cosmic ray bombardment in the upper atmosphere, so the carbon 14 isotope decays without being replenished.
The researchers found that certain soft tissues — notably blood, nails and hair — had radiocarbon levels identical to the contemporary atmosphere.
Therefore, the radiocarbon level in those tissues post-mortem would indicate the year of death.
Barring any future nuclear detonations, this method should continue to be useful for year-of-birth determinations for people born during the next 10 or 20 years.
Everyone born after that would be expected to have the same level of carbon-14 that prevailed before the nuclear testing era.
However, more testing is needed to confirm that belief. 269, March 2012NCJ 237722 Philip Bulman is a writer and editor at NIJ.
Danielle Mc Leod-Henning is a program manager and physical scientist at NIJ.
Measuring the ratio of C14 to C12 and C13 therefore dates the organic matter for periods back to about eight half-lives of the isotope, 45,000 years.