Gas proportional counting in carbon dating


Archaeology and other human sciences use radiocarbon dating to prove or disprove theories.

Over the years, carbon 14 dating has also found applications in geology, hydrology, geophysics, atmospheric science, oceanography, paleoclimatology and even biomedicine.

The end result is to isolate a contaminant-free chemical fraction of a sample for dating.

For the first 40 years or so, conventional radiocarbon dating involved converting the purified sample into either a gas (COC atoms in the samples, by either gas proportional or liquid scintillation counting, respectively.

This contamination usually comes from the burial environment, but can also come from such things as post-excavation conservation practices.

Pretreatment follows a mixture of physical and chemical processes.

The amount of radiocarbon in the atmosphere has not been constant over time.

By measuring the C in samples from tree-rings that have been dendro-dated, scientists have produced an internationally agreed calibration curve for both the northern and southern hemisphere (Int Cal09 and Sh Cal04, respectively). BCal, Calib, Cal Pal, Ox Cal) can be used to convert a radiocarbon age into a radiocarbon date (Figure 2).

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.

Once produced, it mixes rapidly across each of the hemispheres, quickly entering the terrestrial food chain through photosynthesis, with the result that the C is an unstable (radioactive) isotope, with a half-life of 5730±40 years, the proportion of radiocarbon in the deceased organism decreases over time.

It is by measuring the amount of radiocarbon that remains that scientists are able to estimate the amount of time that has passed since the organism’s death.

Radiocarbon dating is essentially a method designed to measure residual radioactivity.

By knowing how much carbon 14 is left in a sample, the age of the organism when it died can be known. 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.

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.

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