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The new method is based on the fact that over the past 60 years, environmental levels of radiocarbon have been significantly perturbed by mid-20th-century episodes of above-ground nuclear weapons testing.Before the nuclear age, the amount of radiocarbon in the environment varied little in the span of a century.The man's body was recovered and pieces of tissue were studied for their C content by accelerator mass spectroscopy.The best estimate from this dating technique says the man lived between 33 BC. From the ratio, the time since the formation of the rock can be calculated.The technique of comparing the abundance ratio of a radioactive isotope to a reference isotope to determine the age of a material is called radioactive dating.Many isotopes have been studied, probing a wide range of time scales.Now, new applications for the technique are emerging in forensics, thanks to research funded by NIJ and other organizations.In recent years, forensic scientists have started to apply carbon-14 dating to cases in which law enforcement agencies hope to find out the age of a skeleton or other unidentified human remains.
Forensic anthropologists at The University of Arizona took advantage of this fact in a recent study funded by NIJ.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.However, the researchers suggested that soft tissue radiocarbon content would be transferred to, and preserved in, the pupal cases of insects whose larvae feed on these tissues.Such insects are simply another link in the food chain.
Radiocarbon levels in teeth formed before then contained less radiocarbon than expected, so when applied to teeth formed during that period, the method was less precise.