Dating accelerator, sample

A more recently developed technique, known as the accelerator mass spectrometry (AMS) radiocarbon dating technique, based on counting, in a mass spectrometer, the relative amount of radiocarbon to stable carbon isotopes in a sample (see Textbox 10). 

The impact of this new technique, which was called Accelerator Mass Spectrometry (AMS), on the radiocarbon and archaeologist communities, was immediate and revolutionary. The introduction of AMS is indeed recognized by some as the third revolution in radiocarbon dating[22,23] and it has provided the opportunity to date very precious finds by collecting very small samples. The interest in developing the technique of AMS was so evident that, just few years after the measurements cited above, a first dedicated AMS system (based on a tandem accelerator) was designed and built [24] then, the first dedicated... 

Sample Preparation for Electrostatic Accelerator Dating of Radiocarbon... 

Graphite produces the large beam currents desirable in electrostatic accelerator dating of radiocarbon. However, samples to be dated can be converted to other forms of carbon with less effort, and still provide satisfactory results. 

The cracking method is possible, as the amorphous carbon does give high nonoampere ion currents. However, the problem of isotopic fractionation, when cracking of the gas is incomplete, has yet to be studied completely. The method is somewhat wasteful, as not all of the gas sample is cracked, and so the full potential of the accelerator-dating method is not realized. 

Rubin, M., Sample Preparation for Electrostatic Accelerator Dating of Radiocarbon, Chapter 5 in this book. 

It is necessary to calibrate the 14C time scale for greater dating accuracy. However, the second-order variations are at least as important as the first-order constancy of atmospheric 14C. For example, they provide a record of prehistoric solar variations, changes in the Earth s dipole moment and an insight into the fate of C02 from fossil fuel combustion. Improved techniques are needed that will enable the precise measurement of small cellulose samples from single tree rings. The tandem accelerator mass spectrometer (TAMS) may fill this need. 

In order to provide AMS analyses to the broad ocean sciences research community, the National Ocean Sciences Accelerator Mass Spectrometry Facility (NOSAMS) was established at Woods Hole Oceanographic Institution (Massachusetts) in 1989. Studies performed there include identification of sources of carbon-bearing materials in the water column and sediment, dating of sedimentary samples, investigations of paleocirculation patterns (e.g., from observations of differences in 14C relative abundances in planktonic and benthic foraminifera, and coral cores and cross sections), as well as studies of modern oceanic carbon cycling and circulation. In fact, much that is known about advective and diffusive processes in the ocean comes from measurements of chemical tracers, such as 14C, rather than from direct measurements of water mass flow. 

Once a starting point has been identified, the analyst should evaluate the appropriateness of the procedure for impurities applications by first examining the pnrity of the analyte peak using a mnltidimensional detector snch as a photodiode array or mass spectrometer. The time to complete these initial evalnations can be accelerated by working with samples that have not been pnrified to the level intended for clinical application (also known as dirty samples.) Any impurities that are found shonld be identified by relative retention time and peak area so that they can nndergo additional characterization at a later date. 

AMS) measurement of atoms (which provides concentrations). The development of linear accelerator mass spectrometer has significantly increased the sensitivity of measurements, leading to an increase of the limit of ages to be dated, but more significantly to a decrease of sample size to be measured and the measurement time. 

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