Radiocarbon dating also referred to as carbon dating or carbon dating is a method for determining the age of an object containing organic material by using the properties of radiocarbon , a radioactive isotope of carbon. The method was developed in the late s by Willard Libby , who received the Nobel Prize in Chemistry for his work in It is based on the fact that radiocarbon 14 C is constantly being created in the atmosphere by the interaction of cosmic rays with atmospheric nitrogen. The resulting 14 C combines with atmospheric oxygen to form radioactive carbon dioxide , which is incorporated into plants by photosynthesis ; animals then acquire 14 C by eating the plants. When the animal or plant dies, it stops exchanging carbon with its environment, and from that point onwards the amount of 14 C it contains begins to decrease as the 14 C undergoes radioactive decay.
This is done by conversion to carbon dioxide with subsequent graphitization in the presence of a metal catalyst. Burning the samples to convert them into graphite, however, also introduces other elements into the sample like nitrogen When the samples have finally been converted into few milligrams of graphite, they are pressed on to a metal disc.
Reference materials are also pressed on metal discs. These metal discs are then mounted on a target wheel so they can be analyzed in sequence. Ions from a cesium gun are then fired at the target wheel, producing negatively ionized carbon atoms.
These negatively ionized carbon atoms pass through focusing devices and an injection magnet before reaching the tandem accelerator where they are accelerated to the positive terminal by a voltage difference of two million volts.Radiocarbon Dating
At this stage, other negatively charged atoms are unstable and cannot reach the detector. The negatively charged carbon atoms, however, move on to the stripper a gas or a metal foil where they lose the electrons and emerge as the triple, positively charged carbon atoms.
At this stage, molecules that may be present are eliminated because they cannot exist in this triple charged state. The carbon atoms with triple positive charge further accelerate away from the positive terminal and pass through another set of focusing devices where mass analysis occurs.
In mass analysis, a magnetic field is applied to these moving charged particles, which causes the particles to deflect from the path they are traveling.
How Does Carbon Dating Work
If the charged particles have the same velocity but different masses, as in the case of the carbon isotopes, the heavier particles are deflected least. Detectors at different angles of deflection then count the particles.
At the end of an AMS run, data gathered is not only the number of carbon 14 atoms in the sample but also the quantity of carbon 12 and carbon From these data, concentration ratio of the isotopes can be known to allow evaluation of the level of fractionation. The greatest advantage that AMS radiocarbon dating has over radiometric methods is small sample size.
Accelerator mass spectrometers need only as little as 20 milligrams and as high as milligrams for certain samples whereas conventional methods need at least 10 grams in samples like wood and charcoal and as much as grams in bones and sediments.
Accelerator mass spectrometers typically need sample sizes lesser than conventional methods by a factor of 1, Radiocarbon dating is a destructive process. Hence, because of its ability to analyze samples even in minute amounts, accelerator mass spectrometry is the method of choice for archaeologists with small artifacts and those who cannot destroy very expensive or rare materials.
Scientific instrument used for carbon dating
Due to the sensitivity of accelerator mass spectrometers, carbon dating small particles like blood particles, a grain, or a seed have been made possible. Accelerator mass spectrometry also takes less time to analyze samples for carbon 14 content compared to radiometric dating methods that can take one or two days.
An accelerator mass spectrometer has a run time of a few hours per sample. Lastly, it must be noted that AMS measurements usually achieve higher precision and lower backgrounds than radiometric dating methods. An accelerator mass spectrometer, although a powerful tool, is also a costly one. Establishing and maintaining an accelerator mass spectrometer costs millions of dollars. Due to the small sample sizes involved, control of contaminants is also difficult.
Rigorous pretreatment is needed to make sure contaminants have been eliminated and will not lead to substantial errors during the carbon dating process.
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Please sign in to add a comment. Registration is free, and takes less than a minute. Fossil fuel emissions will complicate radiocarbon dating, warns scientist July 20, Fossil fuel emissions could soon make it impossible for radiocarbon dating to distinguish new materials from artefacts that are hundreds of years old.
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