Mailing Address: Attn: Assoc. Prof. Alan Hogg or Dr. Fiona Petchey Waikato Radiocarbon Dating Laboratory, The University of Waikato, Gate 9, Hillcrest Road.
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- Staff - Waikato Radiocarbon Dating - Faculty of Science and Engineering: University of Waikato
- Waikato Radiocarbon Dating Laboratory
They have masses of 13 and 14 respectively and are referred to as "carbon" and "carbon If two atoms have equal numbers of protons but differing numbers of neutrons, one is said to be an "isotope" of the other. Carbon and carbon are thus isotopes of carbon Isotopes participate in the same chemical reactions but often at differing rates. When isotopes are to be designated specifically, the chemical symbol is expanded to identify the mass for example, 13 C.
Both 13 C and 14 C are present in nature.
The abundance of 14 C varies from 0. The highest abundances of 14 C are found in atmospheric carbon dioxide and in products made from atmospheric carbon dioxide for example, plants. Unlike 12 C and 13 C, 14 C is not stable.
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- What is Carbon Dating??
As a result it is always undergoing natural radioactive decay while the abundances of the other isotopes are unchanged. Carbon is most abundant in atmospheric carbon dioxide because it is constantly being produced by collisions between nitrogen atoms and cosmic rays at the upper limits of the atmosphere. The rate at which 14 C decays is absolutely constant.
Given any set of 14 C atoms, half of them will decay in years. Since this rate is slow relative to the movement of carbon through food chains from plants to animals to bacteria all carbon in biomass at earth's surface contains atmospheric levels of 14 C. However, as soon as any carbon drops out of the cycle of biological processes - for example, through burial in mud or soil - the abundance of 14 C begins to decline.
Staff - Waikato Radiocarbon Dating - Faculty of Science and Engineering: University of Waikato
After years only half remains. After another years only a quarter remains. This process, which continues until no 14 C remains, is the basis of carbon dating. In order to work on this ancient wood, however, Dr Hogg says they had to refine their techniques, and made significant advances as a result. There are two ways to count C Dr Hogg mostly works with radiometric methods, which involve counting the bursts of radiation given off when a C14 atom decays.
The older a sample is, the fewer C14 atoms remain, and the fewer radioactive decays there are. Carbon dating can only be performed on material less than about 60, years old; any older than this and there is insufficient C14 to count. With the other technique, known as accelerator mass spectrometry AMS , the carbon 14 atoms are separated from the more common, non-radioactive carbon 12 on the basis of their mass, and counted directly.
Dr Hogg says the two techniques each have their strengths and weaknesses. AMS requires very small samples, less than a tenth of a gram. They require less pre-treatment, and you can handle 10 or 20 samples at once, which keeps the cost down.
Waikato Radiocarbon Dating Laboratory
To achieve the precision needed to work on ancient wood, the laboratory used samples that were three times as large as normal. Vials containing the material to be dated had to be larger, and manufactured to exact specifications from synthetic silica imported from Germany. The laboratory also developed high-quality, impervious stoppers for the vials, which they now sell to other carbon dating labs overseas.
Radiometric dating is a long, convoluted process.