Abstracts of the 7th International AMS Conference

Abstract

The AMS program at the S. Paulo 9MV Tandem accelerator has been initiated with major emphasis on projects based on the determination of 10Be, 26Al and 36C1 concentrations. A first report on this program was presented at the AMS Conference in Canberra (Tenreiro et al. 1994). Since then, progress has been achieved on the improvement of the voltage stability of the 8UD-9MV terminal and the ionic optics, controlled only by electrostatic elements, except for the analyzing magnet. An automatic system for changing beams of different isotopes has been developed, allowing the rejection of the stable beams before they reach the detector placed at the beam direction. The group from the Fluminense Federal University (UFF), in Niteroi, has helped in the design and construction of a new Bragg gas chamber detector, coupled with an E X DE telescope and a time-of-flight system. A new scattering chamber has also been designed at UFF, and it will be fully dedicated to the AMS program. Beams of 26A1 were produced via the 26Mg (p,n) 26Al reaction; 36C1 beams were produced from samples prepared from sea water from different places in South America and placed at a Cssputtering ion source. Both beams were successfully accelerated and detected. Recently, another group, from the Londrina State University, has joined the Brazilian AMS project. The main research programs related with the AMS technique, in Brazil, are based on Geological and Oceanographical studies. REFERENCE Tenreiro, C. et al. 1994 Nuclear Instruments and Methods in Physics Research B92. AMS SAMPLE HANDLING IN GRONINGENA. T. AERTS-BIJMA, H. MEIJER and J. VAN As is the case with the Groningen conventional laboratory, the AMS laboratory handles ca. 1000 samples annually such as water (DIC/DOC from groundwater and the ocean), marine carbonates, atmospheric C02, organic deposits such as peat, soils and macrofossils, and the complete spectrum of archaeological datable materials.The organic samples are combusted in a CN-analyzer, consisting of a flash combustion/purification unit and on-line mass spectrometer. The CO2 is trapped cryogenically and transferred to the graphitization setup. We employ one 10-fold and one 15-fold graphitization systems (ranging from 3 to 8 Since 1985, more than 5000 samples have been 14C dated with the Utrecht AMS facility. In this paper the present status of preparation, measurement and data analysis is discussed. A routine procedure is followed for samples of at least 0.5 mg carbon. The 14C/12C and the 13C/12C ratio are measured and normalized on those of the NOX standard. The AMS-measured S13C value is used to monitor the measurement and must agree within 1-2 a with that from conventional mass-spectrometry.Contamination in preparation and measurement is corrected for on the basis of the average value observed for the blanks (0.18-0.06 pMC). In routine 14C measurements on (sub)recent materials, the overall precision is ca. 0.4%. Measurements on samples containing <200 µg carbon reveal mass dependence in two respects: 1) the 14C/12C of a blank in...