Accelerator mass spectrometry sample size

Accelerator mass spectrometry (AMS) is useful to measure extremely low-abundance nuclides (isotope ratio of 10 to 10 relative to its stable isotope), such as Be, C, A1, C1, " Ca, and I, in natural samples. Small amounts of C and T can be measured by AMS on mg size samples of carbon and iodine extracted from 500-ml seawater samples (Povinec et al. 2000). Neutron activation analysis (NAA), radiochemical neutron activation analysis (RNAA), and inductively coupled plasma mass spectrometry (ICP-MS) are useful for the determination of ultra-trace Th and U in geological and cosmochemical samples, and for determination of the concentration of Pu and Pu. Reference marine-biological samples are necessary to test the performance of the analytical methods employed in surveying and monitoring radioactive materials in the sea. An ocean shellfish composite material containing 0.1% w/w Irish Sea mussel, 12% w/w White Sea mussel, and 87.9% w/w Japan Sea oyster has been prepared as the NIST SRM 4358 (The National Institute of Standards and Technology, SRM) in the natural-matrix, environmental-level radioactive SRM series (Altzitzoglou 2000). This NIST SRM 4358 sample will be useful for the determination of the activity of K, Cs, Pb, Ra, Th, and Am. 

Next, low-temperature (<150°C), low-pressure torr) oxygen plasmas oxidized organic components of the sample to CO2. Decomposition of inorganic carbon present (dolomitic limestone rock and calcite/calcium oxalate accretions) was prevented by running the plasmas at low-temperature. Carbon dioxide from the sample was flame-sealed into a glass tube cooled to liquid nitrogen temperature (-194°C), after water had been frozen out with a dry-ice/ethanol slurry (-58°C), and finally sent for radiocarbon analysis at the Center for Accelerator Mass Spectrometry at the Lawrence Livermore National Laboratory (LLNL-CAMS). It was necessary to utilize an AMS measurement due to the small sample size. 

Mass spectrometry using alternative ionization and sample preparation methods are employed in ink and paint analysis. The oldest of these techniques is based on pjnrolysis of the sample (typically, a paint) prior to its introduction into the GC. Detectors for PyGC are and FID. Pyrolysis patterns can be examined in the same way accelerant patterns are (Chapter 10), but increasingly, GCMS is preferred over FID. Pyrolysis is, by definition, destructive, but the sample size is reasonably small, and recently a micropyrolysis GCMS has been developed and applied to photocopier toners and paint. A laser is focused on the sample through a microscope, and the pyrolysis vapor product is directed into the GCMS system. The pattern of the pyrolyzates and chemical composition... 

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