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 to1963 produced a dramatic surge in the amount of radiocarbon in the atmosphere, Buchholz said.
"Even though the detonations were conducted at only a few locations, the elevated carbon-14 levels in the atmosphere rapidly equalized around the globe," he said. 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 analyzed 33 teeth from 22 different people whose ages were known. The enamel separations were done at the Karolinska Institute, and sample preparation and accelerator mass spectrometry analysis was done at Lawrence Livermore.
The enamel dating technique doesn't work for people born before 1943, because all of their teeth would have been formed before testing began in 1955.
In their Nature paper, Buchholz and his colleagues note that the technique for carbon-14 analysis using accelerator mass spectrometry is becoming increasingly sensitive and inexpensive, suggesting that even
Source:DOE/Lawrence Livermore National Laboratory