Gas proportional counting in carbon dating
When both of the detectors present pick up the flash, it is counted and used to calculate the amount of carbon-14 present.
AMS has become the standard in the industry for measuring carbon-14 content and offers several advantages over radiometric techniques.
There have been different methods of measuring carbon-14 since Willard Libby pioneered the radiocarbon dating technique in the 1940s – from the radiometric techniques of gas proportional counting and liquid scintillation counting to the more recent accelerator mass spectrometry (AMS).
When the weakly radioactive carbon-14 decays, it undergoes beta (β) decay producing nitrogen-14 and a beta particle.
This scintillator produces a flash of light when it interacts with a beta particle.
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.
In contrast, it measures the carbon-14 directly, relative to the carbon-12 and carbon-13 present, rather than measuring the products of its radioactive decay.
The minimum sample requirements for AMS dating are significantly smaller than for radiometric dating techniques, allowing even a few milligrams of sample to be dated for certain sample types.
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.
By knowing how much carbon 14 is left in a sample, the age of the organism when it died can be known.
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.
Over the years, carbon 14 dating has also found applications in geology, hydrology, geophysics, atmospheric science, oceanography, paleoclimatology and even biomedicine.
Radiocarbon, or carbon 14, is an isotope of the element carbon that is unstable and weakly radioactive. Carbon 14 is continually being formed in the upper atmosphere by the effect of cosmic ray neutrons on nitrogen 14 atoms.