LIVERMORE , Calif. – The radioactive carbon-14 produced byabove-ground nuclear testing in the 1950s and 1960s is providingforensic scientists with a more precise way to determine a person’s ageat the time of death. The method could help in the identification ofvictims of Hurricane Katrina and other large-scale disasters.
Thenew technique, developed by researchers at Lawrence Livermore NationalLaboratory (LLNL) and the Karolinska Institute in Sweden, determinesthe amount of carbon-14 in tooth enamel. Scientists can relate theextensive atmospheric record for carbon-14 to when the tooth was formedand calculate the age of the tooth, and its owner, to an accuracy ofwithin about 1.6 years.
“Unlike most other tissue, dental enameldoesn’t turn over,” said Bruce Buchholz of LLNL’s Center forAccelerator Mass Spectrometry, where the enamel samples were analyzed.“Whatever carbon gets laid down in enamel during tooth formation staysthere, so tooth enamel is a very good chronometer of the time offormation.
“We were surprised at how well it worked,” he said.“And if you look at multiple teeth formed at different times, you canget (the age range) even tighter.” Previous techniques, such asevaluating skeletal remains and tooth wear, are accurate only to withinfive to 10 years in adults, Buchholz said.
The research was reported in this week’s edition of the journal Nature.
Buchholzsaid Swedish forensic scientists already have used enamel dating tohelp narrow the search for victims of last December’s tsunami inSoutheast Asia. “After a few days in the water, it’s very hard toidentify someone,” he said. “You can’t use (enamel dating) to identifya person – that requires a DNA analysis – but you can narrow down thenumber of people you need to look at from a list of missing people.”
Livermoreofficials are providing information on the enamel dating technique tofederal agencies as part of the Laboratory’s scientific and technicalassistance in response to Hurricane Katrina. LLNL also is assisting insetting up emergency high-bandwidth communications and wirelessnetworks. The Laboratory’s Micropower-Impulse Radar (MIR) technologyalso is being deployed to assist search and rescue crews in locatinghurricane victims. This same technology was deployed in the daysfollowing the September 11 attacks in New York’s World Trade Centerrubble.
Carbon-14, or radiocarbon, is naturally produced bycosmic ray interactions with air and is present at low levels in theatmosphere and food. Atmospheric testing of nuclear weapons from 1955to1963 produced a dramatic surge in the amount of radiocarbon in theatmosphere, Buchholz said.
“Even though the detonations wereconducted at only a few locations, the elevated carbon-14 levels in theatmosphere rapidly equalized around the globe,” he said. Sinceatmospheric testing was banned in 1963, the levels have droppedsubstantially as the carbon-14 reacted with oxygen to form carbondioxide, which was taken up by plants during photosynthesis and mixedwith the oceans.
“Because we eat plants and animals that live offplants, the carbon-14 concentration in our bodies closely parallelsthat in the atmosphere at any one time,” he said.
Buchholz andhis colleagues analyzed 33 teeth from 22 different people whose ageswere known. The enamel separations were done at the KarolinskaInstitute, and sample preparation and accelerator mass spectrometryanalysis was done at Lawrence Livermore.
The enamel datingtechnique doesn’t work for people born before 1943, because all oftheir teeth would have been formed before testing began in 1955.
Intheir Nature paper, Buchholz and his colleagues note that the techniquefor carbon-14 analysis using accelerator mass spectrometry is becomingincreasingly sensitive and inexpensive, suggesting that even thoughnuclear testing was conducted decades ago, enamel dating could be usedfor precise age determination “for a long time to come.”
Foundedin 1952, Lawrence Livermore National Laboratory has a mission to ensurenational security and to apply science and technology to the importantissues of our time. Lawrence Livermore National Laboratory is managedby the University of California for the U.S. Department of Energy'sNational Nuclear Security Administration.
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