14c isotope dating
The sample passes through several accelerators in order to remove as many atoms as possible until the C pass into the detector.These latter atoms are used as part of the calibration process to measure the relative number of isotopes (9).
This does not mean that we have a precise year of 3780BC, it means we then need to calibrate through other methods that will show us how atmospheric concentrations of the C isotope has changed - most typically through the dendrochronology records (tree ring data) (10).
Very old trees such as North American Bristlecone Pine are ideal for constructing long and accurate records of the state of the atmosphere.
AMS works slightly differently; it converts the atoms of the sample into fast-moving ions so that they become charged atoms.
By applying magnetic and electrical fields, the mass of these ions is measured and the accelerator is used to remove ions that might contaminate the dating.
It is presumed that the proportion of atmospheric C is the same today as it was in 1950 (10), (11) and that the half-life remains the same.
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If a radioactivity level comes back as half of what would have been expected if the organism had died in 1950, then it is presumed to be 5,730 years before 1950.This allows researchers to account for variation by comparing the known records of C levels in the tree record, looking for a tree record that has the same proportion of radiocarbon.The overlapping nature of the tree records means this is the most accurate record we have.When the half-life was corrected in 1950, the year was taken as a base date from which to calculate all resulting dates.Therefore, any expression of “before present” will mean “before 1950”.Radiocarbon dating is simply a measure of the level of C isotopes in the atmosphere can vary.This is why calibration against objects whose age is known is required (14).Radiocarbon dating may only be used on organic materials.Typically (6): The above list is not exhaustive; most organic material is suitable so long as it is of sufficient age and has not mineralised - dinosaur bones are out as they no longer have any carbon left.Archaeologists had used Relative Dating methods to calculate their reigns.Though their initial calculations were slightly incorrect thanks to the contaminants of extensive nuclear testing of the age, scientists soon discovered the error and developed methods that were more accurate, including a date of calibration to 1950.