The researchers found that if they assumed tooth enamel radiocarbon content to be determined by the atmospheric level at the time the tooth was formed, then they could deduce the year of birth.
Although neutrons do not carry an electrical charge, they have a mass comparable to that of protons, so different isotopes have different atomic weight. Because of the different number of neutrons, carbon-12 and carbon-14 differ with respect to radioactivity. Carbon-14, on the other hand, undergoes radioactive decay:e (half-life is 5720 years)The other common isotope of carbon is carbon-13.
Carbon-13 has 6 protons, just like other carbon isotopes, but it has 7 neutrons. Although 15 isotopes of carbon are known, the natural form of the element consists of a mixture of only three of them: carbon-12, carbon-13, and carbon-14. Measuring the difference in the radio between carbon-12 and carbon-14 is useful for dating the age of organic matter since a living organism is exchanging carbon and maintaining a certain ratio of isotopes.
The researchers wanted to find out if they could identify a person's year of birth or year of death using precise measurements of carbon-14 levels in different post-mortem tissues.
They measured carbon-14 levels in various tissues from 36 humans whose birth and death dates were known.
In contrast, from 1955 to 1963, atmospheric radiocarbon levels almost doubled.
Since then they have been dropping back toward natural levels.Carbon-12 and carbon-14 are two isotopes of the element carbon.The difference between carbon-12 and carbon-14 is the number of neutrons in each atom.Barring any future nuclear detonations, this method should continue to be useful for year-of-birth determinations for people born during the next 10 or 20 years.Everyone born after that would be expected to have the same level of carbon-14 that prevailed before the nuclear testing era.Unlike tooth enamel, soft tissues are constantly being made and remade during life.