Establishing Natural Product Content with the Natural Radiocarbon Signature

摘要

Radiocarbon (~(14)C) is produced naturally at relatively constant levels in the atmosphere by cosmic ray interactions with nitrogen. Isolated carbon atoms are quickly oxidized to CO_2 in the atmosphere and are incorporated into biomolecules. Above ground nuclear weapons testing between 1955-63 caused a pulse in the ~(14)C content of the atmosphere over the past 55 years, but it is now almost back to the 1950 level. All living things are labeled with ~(14)C while alive and retain the isotopic signature at death and when processed into food. Carbon from petroleum sources is devoid of ~(14)C and easily distinguished from natural biological sources (~(14)C/C = 1.2 parts per trillion) by accelerator mass spectrometry (AMS). We will briefly explain how AMS works and present examples of how it is used to determine natural and fossil carbon content of food. We will also describe how AMS can be used to verify if a claimed vintage is consistent with its isotopic signature.