In this method, the carbon 14 content is directly measured relative to the carbon 12 and carbon 13 present. Some inorganic matter, like a shell’s aragonite component, can also be dated as long as the mineral’s formation involved assimilation of carbon 14 in equilibrium with the atmosphere.
The method does not count beta particles but the number of carbon atoms present in the sample and the proportion of the isotopes. Samples that have been radiocarbon dated since the inception of the method include charcoal, wood, twigs, seeds, bones, shells, leather, peat, lake mud, soil, hair, pottery, pollen, wall paintings, corals, blood residues, fabrics, paper or parchment, resins, and water, among others.
Physical and chemical pretreatments are done on these materials to remove possible contaminants before they are analyzed for their radiocarbon content.
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.Radioactivity is the emission of atomic particles and/or radiation by atoms that are unstable and may undergo radioactive decay into a different element.It was not "invented" but "discovered." French scientist Henri Bequerel in 1896 compared these emissions to X-rays (discovered and studied by German physicist Wilhelm Roentgen in 1895).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.
When the stocks of Oxalic Acid I were almost fully consumed, another standard was made from a crop of 1977 French beet molasses.
Plants and animals assimilate carbon 14 from carbon dioxide throughout their lifetimes.
When they die, they stop exchanging carbon with the biosphere and their carbon 14 content then starts to decrease at a rate determined by the law of radioactive decay.
Pioneering research in radioactivity was done by Pierre and Marie Curie, Ernest Rutherford, Paul Villard, and Frederick Soddy (a student of Rutherford).
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.
It must be noted though that radiocarbon dating results indicate when the organism was alive but not when a material from that organism was used.