TY - CONF T1 - Microscale AMS (super 14) C measurement at NOSAMS Y1 - 1998 A1 - Pearson, Ann A1 - McNichol, Ann P. A1 - Schneider, Robert J. A1 - von Reden, Karl F. A1 - Zheng, Yan KW - 03 KW - absolute age KW - accelerator mass spectroscopy KW - accuracy KW - C-14 KW - C-14/C-12 KW - carbon KW - Carbon dioxide KW - combustion KW - data processing KW - Geochronology KW - graphite KW - isotope fractionation KW - isotopes KW - mass spectroscopy KW - mathematical methods KW - methods KW - native elements KW - radioactive isotopes KW - sample preparation KW - size KW - spectroscopy KW - Stable isotopes AB - Techniques for making precise and accurate radiocarbon accelerator mass spectrometry (AMS) measurements on samples containing less than a few hundred micrograms of carbon are being developed at the NOSAMS facility. A detailed examination of all aspects of the sample preparation and data analysis process shows encouraging results. Small quantities of CO (sub 2) are reduced to graphite over cobalt catalyst at an optimal temperature of 605 degrees C. Measured (super 14) C/ (super 12) C ratios of the resulting targets are affected by machine-induced isotopic fractionation, which appears directly related to the decrease in ion current generated by the smaller sample sizes. It is possible to compensate effectively for this fractionation by measuring samples relative to small standards of identical size. Examination of the various potential sources of background (super 14) C contamination indicates that the sample combustion process is the largest contributor, adding ca. 1 mu g of carbon with a less-than-modern (super 14) C concentration. PB - University of Arizona, Department of Geosciences, Tucson, AZ, United States (USA) CY - United States (USA) VL - 40 UR - http://hdl.handle.net/10150/653650 N1 - id: 2237; Source type: conferencepapers&proceedings; Object type: Article; Object type: Conference Paper; Copyright: GeoRef, Copyright 2007, American Geological Institute.; CSAUnique: 1999-044438; AccNum: 1999-044438; ISSN: 0033-8222; CODEN: RACAAT ER -