• 10Be Analyses with a Compact AMS Facility—Are BeF2 Samples the Solution?

      Wacker, L.; Grajcar, M.; Ivy-Ochs, S.; Kubik, PW; Suter, M. (Department of Geosciences, The University of Arizona, 2004-01-01)
      The injection of 10BeFinstead of10BeOinto a compact accelerator mass spectrometry system with a terminal voltage of 0.58 MV was investigated, because BFmolecules are unstable and isobaric interference of 10B with 10Be can thus be significantly reduced. We describe the method we developed to prepare BeF2samples. 10Be was measured in a segmented gas ionization detector. Separation of 10Be from 10B could be achieved both for ions in the 1+ charge state with an energy of 0.8 MeV and in the 2+ charge state with an energy of 1.4 MeV. The 2+ ions are better separated, whereas the 1+ charge state has a higher transmission. 10Be/9Be ratios (approximately 10^-12) in a suite of rock samples were successfully determined for exposure dating in either charge state and compared with measurements made on the 6MV tandem.
    • A Gas Ion Source for Radiocarbon Measurements at 200 kV

      Ruff, M.; Wacker, L.; Gäggeler, H. W.; Ter, M.; Synal, H.-A.; Szidat, S. (Department of Geosciences, The University of Arizona, 2007-01-01)
      The novel tabletop miniaturized radiocarbon dating system (MICADAS) at ETH Zurich features a hybrid Cs sputter negative ion source for the measurement of solid graphite and gaseous CO2 samples. The source produces stable currents of up to 6 A C out of gaseous samples with an efficiency of 36%. A gas feeding system has been set up that enables constant dosing of CO2 into the Cs sputter ion source and ensures stable measuring conditions. The system is based on a syringe in which CO2 gas is mixed with He and then pressed continuously into the ion source at a constant flow rate. Minimized volumes allow feeding samples of 330 g carbon quantitatively into the ion source. In order to test the performance of the system, several standards and blanks have successfully been measured. The ratios of 14C/12C could be repeated within statistical errors to better than 1.0% and the 13C/12C ratios to better than 0.2%. The blank was 1 pMC.
    • A Preparative 2D-Chromatography Method for Compound-Specific Radiocarbon Analysis of Dicarboxylic Acids in Aerosols

      Fahrni, S. M.; Ruff, M.; Wacker, L.; Perron, N.; Gäggeler, H. W.; Szidat, S. (Department of Geosciences, The University of Arizona, 2010-01-01)
      There is a great scientific demand for an assessment of the sources and formation processes of atmospheric carbonaceous aerosols since they strongly influence the global radiation balance and affect public health. Much attention in atmospheric studies has been paid to dicarboxylic acids (DCAs) due to their abundance at substantially different sites and their potential influence on cloud formation processes. Nevertheless, sources of oxalic acid (HOOCCOOH) and other DCAs are not well understood yet. In order to quantify contributions of fossil and non-fossil sources, a method for the preparative separation of oxalic acid and other DCAs from aerosols for compound-specific radiocarbon analysis (CSRA) has been developed. This method consists of a water extraction of aerosols collected on quartz-fiber filters followed by 2 consecutive liquid chromatography (LC) steps on different chromatography columns (2D-chromatography). Through the use of aqueous, completely non-organic eluents and single injections into liquid chromatography, low blank levels are achieved with total oxalic acid recoveries of up to 66%. Upon separation, 14C measurements of small samples (containing typically 10-20 g carbon) are conducted at the gas ion source of the 200kV accelerator mass spectrometry facility MICADAS. The method is verified with processed reference materials, artificial mixtures of oxalic acid with typical matrix components, and a standard addition of ambient aerosols. Two exemplary field samples show dominant non-fossil sources of oxalic acid.
    • Are Compact AMS Facilities a Competitive Alternative to Larger Tandem Accelerators?

      Suter, M.; Müller, A. M.; Alfimov, V.; Christl, M.; Schulze-König, T.; Kubik, P. W.; Synal, H.-A.; Vockenhuber, C.; Wacker, L. (Department of Geosciences, The University of Arizona, 2010-01-01)
      In the last decade, small and compact accelerator mass spectrometry (AMS) systems became available operating at terminal voltages of 1 MV and below. This new category of instruments has become competitive for radiocarbon detection to larger tandem accelerators and many of these instruments are successfully used for 14C dating or biomedical applications. The AMS group at ETH Zurich has demonstrated that small instruments can be built, which allow measurements also of other radionuclides such as 10Be, 26Al, 129I, and the actinides. 41Ca measurements can be performed with sufficient sensitivity for biomedical applications. A summary of recent developments made at the 500kV Pelletron in Zurich is given and its performance is compared with that of a commercial compact instrument from the company High Voltage Engineering Europe (HVEE) in Amersfoort, the Netherlands, operating at 1MV at CNA in Seville, Spain, as well as with that of larger AMS facilities. It turns out that the ion optics, stripper design, and the detection system are critical for the performance.
    • MICADAS: Routine and High-Precision Radiocarbon Dating

      Wacker, L.; Bonani, G.; Friedrich, M.; Hajdas, I.; Kromer, B.; Němec, N.; Ruff, M.; Suter, M.; Synal, H.-A.; Vockenhuber, C. (Department of Geosciences, The University of Arizona, 2010-01-01)
      The prototype mini carbon dating system (MICADAS) at ETH Zurich has been in routine operation for almost 2 yr. Because of its simple and compact layout, setting up a radiocarbon measurement is fast and the system runs very reliably over days or even weeks without retuning. The stability of the instrument is responsible for the good performance in highest-precision measurements where results of single samples can be reproduced within less than 2. The measurements are described and the performance of MICADAS is demonstrated on measured data.
    • On-Line Radiocarbon Measurements of Small Samples Using Elemental Analyzer and MICADAS Gas Ion Source

      Ruff, M.; Fahrni, S.; Gaggeler, H. W.; Hajdas, I.; Suter, M.; Synal, H-A; Szidat, S.; Wacker, L. (Department of Geosciences, The University of Arizona, 2010-01-01)
      An on-line measurement system was installed at the MICADAS in Zurich, using an elemental analyzer (EA) as a combustion unit to enable direct radiocarbon measurement of samples containing carbon in the range of 5-100 g possible with minimum effort. The samples are combusted in small capsules and the gaseous combustion products are separated by the EA. The carbon dioxide leaving the EA in a high helium flow is concentrated on a small external trap containing X13 zeolite adsorber material. This new concept, avoiding a cryogenic trapping for the enrichment step, allows the construction of a very compact system able to work even with the smallest samples. Concentrated on the external trap, the carbon dioxide is flushed into the gas-tight syringe of our gas inlet system using a low helium stream. The gas mixture is measured with the MICADAS gas ion source. Several different sample capsules were analyzed to minimize the major blank contribution coming from the sample vessel. The best results were achieved with 25-L tin capsules, which contained only 0.34 0.13 g carbon at 65 pMC. This work describes the development of the on-line system and the protocol for measurement runs. Results are presented for on-line measurements of reference materials and a comparison is performed with typical dating samples measured previously as graphite targets. Finally, relevance and limitations of on-line measurements are discussed.
    • Source Apportionment of Aerosols by 14C Measurements in Different Carbonaceous Particle Fractions

      Szidat, S.; Jenk, T. M.; Gäggeler, H. W.; Synal, H.-A.; Fisseha, R.; Baltensperger, U.; Kalberer, K.; Samburova, V.; Wacker, L.; Saurer, M.; et al. (Department of Geosciences, The University of Arizona, 2004-01-01)
      Radiocarbon enables a distinction between contemporary and fossil carbon, which can be used for the apportionment of biogenic and anthropogenic sources in environmental studies. In order to apply this approach to carbonaceous atmospheric aerosols, it is necessary to adapt pretreatment procedures to the requirements of 14C measurements. In this work, we followed an approach in which total carbon (TC) is subdivided into fractions of different chemical and physical properties. 14C data of ambient aerosols from Zrich (Switzerland) are presented for the 2 sub-fractions of TC, organic carbon (OC) and elemental carbon (EC). Furthermore, OC is separated into water-insoluble OC (WINSOC) and water-soluble OC (WSOC). Results demonstrate the importance to differentiate between these fractions for 14C-deduced source apportionment, as the contributions can range between both extremes, nearly exclusively biogenic and anthropogenic.
    • Towards On-Line 14C Analysis of Carbonaceous Aerosol Fractions

      Perron, N.; Szidat, S.; Fahrni, S.; Ruff, M.; Wacker, L.; Prévôt, A. H.; Baltensperger, U. (Department of Geosciences, The University of Arizona, 2010-01-01)
      Atmospheric carbonaceous aerosol is traditionally divided into organic carbon (OC) and elemental carbon (EC). Their respective carbon amounts are usually analyzed by means of an OC/EC analyzer and their fossil and non-fossil origins can be determined by radiocarbon analysis, which has proven to be a powerful tool for carbonaceous aerosol source apportionment. Thus far, separation of OC and EC has been performed off-line by manual and time-consuming techniques. We present an on-line system that couples a commercial OC/EC analyzer with the gas ion source of the accelerator mass spectrometer (AMS) MICADAS and its CO2 feeding system. The performance achieved with reference materials and blanks are discussed to demonstrate the potential of this coupling for source apportionment of atmospheric carbonaceous particulate matter.