Radiocarbon dating can be used to date
Conversely, contamination by newer plant matter carried by flowing water or intruding plant roots may result in a date that is much too young. The original technique was based on counting the number of individual radioactive decay events per unit of time, using a device similar to a Geiger counter.
Archaeologists are acutely aware of these and other potential difficulties, and take extreme care in the selection and handling of objects to be dated. In the 1970s a new technique was developed called Accelerator-based Mass Spectrometry (AMS), which counts the number of carbon-14 atoms directly.
The proportion of carbon-14 to carbon-12 in the atmosphere therefore remains relatively stable at about 1.5 parts per billion.
One of the implied assumptions in radiocarbon dating is that levels of atmospheric carbon-14 have remained constant over time.
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.
This dramatically improves accuracy, and reduces the amount of carbon required from about 10 grams to only a few milligrams.
In recent years, dating methods based on cosmogenic isotopes other than carbon (such as beryllium-10 and chlorine-36) have been developed, which allow for the dating of a wider variety of objects over much longer time scales.
If the ground in which an object is buried contains particles of coal or other ancient sources of carbon, radiocarbon testing may indicate that the object is far older than it really is.On April 26, 2007 this facility celebrated 25 years of operation, during which time it had processed over 75,000 radiocarbon measurements on objects ranging from the Dead Sea Scrolls to the Shroud of Turin.Their commercial rate (in 2008) is 5.00 per sample, which somewhat limits its accessibility to chronically under-funded archeological research projects.Carbon has an atomic number of 6, an atomic weight of 12.011, and has three isotopes: carbon-12, carbon-13, and carbon-14.(The numbers 12, 13 and 14 refer to the total number of protons plus neutrons in the atom's nucleus.
By knowing how much carbon 14 is left in a sample, the age of the organism when it died can be known.