Conventional radiocarbon dating

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The age of known artefacts from Egypt were too young when measured by radiocarbon dating.

A scientist from the Netherlands (Hessel de Vries) tested this by radiocarbon dating tree rings of know ages (de Vries, 1958).

All radiocarbon laboratories either standardize to the US National Bureau of Standards Oxalic Acid I (OX-I) which is derived from Sugar Beets in 1955 or a secondary standard NBS OX-II (grown in 1977) or Australian National University Sucrose (ANU), which is sugar from the 1974 growing season in Australia.

Both the OX-II and ANU have been extensively cross-calibrated to OX-I and can be used to normalize a sample for radiocarbon dating.

The main limitation of these techniques is sample size, as hundreds of grams of carbon are needed to count enough decaying beta particles.

This is especially true for old samples with low beta activity.

The true half-life of 14C is 5730 years and not the originally measured 5568 years used in the radiocarbon age calculation, and the proportion of 14C in the atmosphere is not consistent through time.

Measuring 14C To obtain the radiocarbon age of a sample it is necessary to determine the proportion of 14C it contains.

Originally this was done by what is known as “conventional” methods, either proportional gas counters or liquid scintillation counters.

The gas counter detects the decaying beta particles from a carbon sample that has been converted to a gas (CO, methane, acetylene).

A liquid scintillation measurement needs the carbon to be converted into benzene, and the instrument then measures the flashes of light (scintillations) as the beta particles interact with a phosphor in the benzene.

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