A new tooth enamel dating technique is providing forensic scientists with a more precise way to determine a person's age at the time of death. The method, which looks at the radioactive carbon-14 produced by above-ground nuclear testing in the 1950s and 960s could be used to help in the identification of victims of Hurricane Katrina and other large-scale disasters. The technique was developed by researchers at Lawrence Livermore National Laboratory (LLNL) and the Karolinska Institute in Sweden, and determines the amount of carbon-14 in tooth enamel. Scientists can relate the extensive atmospheric record for carbon-14 to when the tooth was formed and calculate the age of the tooth, and its owner, to an accuracy of within about 1.6 years.

Bruce Buchholz of LLNL's Center for Accelerator Mass Spectrometry, where the enamel samples were analysed said, “Whatever carbon gets laid down in enamel during tooth formation stays there, so tooth enamel is a very good chronometer of the time of formation. If you look at multiple teeth formed at different times, you can get (the age range) even tighter.” Previous techniques, such as evaluating skeletal remains and tooth wear, are accurate only to within five to 10 years in adults, Buchholz said.

He added that Swedish forensic scientists had already used enamel dating to help narrow the search for victims of last December's tsunami in Southeast Asia. Livermore officials are providing information on the enamel dating technique to federal agencies as part of the Laboratory's scientific and technical assistance in response to Hurricane Katrina. This same technology was deployed in the days following the September 11 attacks in New York's World Trade Center rubble.

Carbon-14, or radiocarbon, is naturally produced by cosmic ray interactions with air and is present at low levels in the atmosphere and food. Atmospheric testing of nuclear weapons from 1955 to 1963 produced a dramatic surge in the amount of radiocarbon in the atmosphere. Buchholz explains, “Even though the detonations were conducted at only a few locations, the elevated carbon-14 levels in the atmosphere rapidly equalised around the globe.”

Since atmospheric testing was banned in 1963, the levels have dropped substantially as the carbon-14 reacted with oxygen to form carbon dioxide, which was taken up by plants during photosynthesis and mixed with the oceans.

“Because we eat plants and animals that live off plants, the carbon-14 concentration in our bodies closely parallels that in the atmosphere at any one time,” he said.

Buchholz and his colleagues analysed 33 teeth from 22 different people whose ages were known. The research was reported in September issue of the journal Nature.