Counting accelerator mass

Soon after this discovery the harnessing of the technique to the measurement of all the U isotopes and all the Th isotopes with great precision immediately opened up the entire field of uranium and thorium decay chain studies. This area of study was formerly the poaching ground for radioactive measurements alone but now became part of the wonderful world of mass spectrometric measurements. (The same transformation took place for radiocarbon from the various radioactive counting schemes to accelerator mass spectrometry.)... 

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). 

R. C. Garner, J. V. Garner, S. Gregory, M. Whattam, A. Calam, D. Leong. Comparison of the absorption of micronized (daflon 500 mg) and nonmicronized 14C-diosmin tablets after oral administration to healthy volunteers by accelerator mass spectrometry and liquid scintillation counting. J. Pharm. Sci. 2002, 91, 32— 40. 

Principal characteristics of small sample liquid scintillation counting (lsc), gas proportional low-level counting (11c) and atom counting by accelerator mass spectrometry (AMS) are summarized in Table 1, and systems we have used are shown in figure 1. The most important differences (apart from cost and availability)... 

Carbon-14 is measured in specialized radioactive counting laboratories and in accelerator-mass spectrometer laboratories. In the first case, relatively large water samples of about 1001 have to be treated, and in the latter case... 

The ratio A/A0 is measured either by P" counting or with the tandem accelerator mass spectrometer (TAMS) in which direct atom counting is used. 

Accelerator mass spectrometry (AMS) extends the capabilities of atom-counting using conventional mass spectrometry, by removing whole-mass molecular interferences without the need for a mass resolution very much better than the mass difference between the atom and its molecular isobar. This technique has been used with great success for the routine measurement of C, Be, " Al, C1 and, recently, (see Table 5.15). Analysis of " C by AMS can, for example, generate dates with a precision that is at least equal to the best conventional beta-particle-counting facility. In many cases, where small sample analysis is required, the AMS method has proved superior (Benkens, 1990). A complete description of AMS can be found in review articles (Litherland et al., 1987 Elmore and Philips, 1978) or recent conference publications. The application of AMS to measurement has been discussed in detail in Kilins et al. (1992). 

To normalize the measurement, the injection magnet is set to accelerate mass 13. The current is measured with a Faraday cup on the high energy side of the accelerator. The counting times are from 10 to 30 s. 

Direct Counting by Tandem Accelerator Mass Spectrometry (37)... 

Measurement Techniques. Light isotopes Concentrations of were determined radiometrically after synthesis of propane (13) in a proportional counter after about twenty-fold electrolytical enrichment of (14), The C content of large samples (. 5 g C) were determined by liquid scintillation counting after synthesis of benzene (15) fi-om CO2 which was extracted fi-om the water sample after acidification. The C content of small samples (<0.5 g C) were measured by accelerator mass spectrometry (AMS) W the Isotrace Laboratory of the University of Toronto. The C, and isotopic... 

Accelerator mass spectrometer (AMS) A huge scientific instrument used for sorting and counting isotopes. AMS dating allows much smaller samples to be used in archaeology. 

Gilman, S.D. et al., Analytical performance of accelerator mass spectrometry and liquid scintillation counting for detection of 14C-labeled atrazine metabolites in human urine,... 

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