Nitrogen isotope dating
An age could be estimated by measuring the amount of carbon-14 present in the sample and comparing this against an internationally used reference standard.The impact of the radiocarbon dating technique on modern man has made it one of the most significant discoveries of the 20th century.
The principal modern standard used by radiocarbon dating labs was the Oxalic Acid I obtained from the National Institute of Standards and Technology in Maryland. Around 95% of the radiocarbon activity of Oxalic Acid I is equal to the measured radiocarbon activity of the absolute radiocarbon standard—a wood in 1890 unaffected by fossil fuel effects.In this method, the carbon 14 content is directly measured relative to the carbon 12 and carbon 13 present.The method does not count beta particles but the number of carbon atoms present in the sample and the proportion of the isotopes.A vial with a sample is passed between two photomultipliers, and only when both devices register the flash of light that a count is made.Accelerator mass spectrometry (AMS) is a modern radiocarbon dating method that is considered to be the more efficient way to measure radiocarbon content of a sample.A radiocarbon measurement is termed a conventional radiocarbon age (CRA).
The CRA conventions include (a) usage of the Libby half-life, (b) usage of Oxalic Acid I or II or any appropriate secondary standard as the modern radiocarbon standard, (c) correction for sample isotopic fractionation to a normalized or base value of -25.0 per mille relative to the ratio of carbon 12/carbon 13 in the carbonate standard VPDB – Cretaceous belemnite formation at Peedee in South Carolina, (d) zero BP (Before Present) is defined as AD 1950, and (e) the assumption that global radiocarbon levels are constant.
Over the years, other secondary radiocarbon standards have been made.
Radiocarbon activity of materials in the background is also determined to remove its contribution from results obtained during a sample analysis.
No other scientific method has managed to revolutionize man’s understanding not only of his present but also of events that already happened thousands of years ago.
Archaeology and other human sciences use radiocarbon dating to prove or disprove theories.
Standard errors are also reported in a radiocarbon dating result, hence the “±” values.