Browsing by Author "Forstner, O"

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    High-sensitivity isobar-free AMS measurements and reference materials for 55Fe, 68Ge and 202gPb
    (Elsevier B.V., 2013-01-01) Wallner, A; Bichler, M; Buczak, K; Fink, D; Forstner, O; Golser, R; Hotchkis, MAC; Klix, A; Krása, A; Kutschera, W; Lederer, C; Plompen, AJM; Priller, A; Schumann, D; Semkova, VM; Steier, P
    Isobaric interference represents one of the major limitations in mass spectrometry. For a few cases in AMS with tandem accelerators, isobaric interference is completely excluded like the well-known major isotopes 14C, 26Al, 129I. Additional isotopes are 55Fe (t1/2=2.74years), 68Ge (t1/2=270.9days) and 202Pb (t1/2=52.5kyr), with 68Ge and 202Pb never been used in AMS so far. Their respective stable isobars, 55Mn, 68Zn and 202Hg do not form stable negative ions. The exceptional sensitivity of AMS for 55Fe, 68Ge and 202gPb offers important insights into such different fields like nuclear astrophysics, fundamental nuclear physics and technological applications. VERA, a dedicated AMS facility is well suited for developing procedures for new and non-standard isotopes. AMS measurements at the VERA facility established low backgrounds for these radionuclides in natural samples. Limits for isotope ratios of <10−15, <10−16 and ⩽2×10−14 were measured for 55Fe/56Fe, 68Ge/70Ge and 202Pb/Pb, respectively. In order to generate accurate isotope ratios of sample materials, AMS relies on the parallel measurement of reference materials with well-known ratios. A new and highly accurate reference material for 55Fe measurements with an uncertainty of ±1.6% was produced from a certified reference solution. In case of 68Ge dedicated neutron activations produced a sufficiently large number of 68Ge atoms that allowed quantifying them through the activity of its decay product 68Ga. Finally, for 202Pb, the short-lived isobar 202Tl was produced via neutron activation and served as a proxy for 202Pb AMS measurements. © 2012 Elsevier B.V.
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    Stable platinum isotope measurements in presolar nanodiamonds by TEAMS
    (Elsevier, 2013-01-01) Wallner, A; Melber, K; Merchel, S; Otte, U; Forstner, O; Gosler, R; Kutschera, W; Priller, A; Steier, P
    Nanodiamonds are stardust grains commonly found in primitive meteorites. They survived the formation of the solar system and kept their own individuality. Measurements of trace-element isotopic signatures in these grains will help understanding heavy element nucleosynthesis in massive stars and dust formation from their ejecta. We have continued previous attempts to search for stable Pt isotope anomalies in nanodiamonds via trace element accelerator mass spectrometry (TEAMS). The installation of a new injector beam line at the VERA facility allowed studying low traces of stable elements in different materials. Moreover, recent experiments showed that VERA provides the required measurement precision together with a low Pt machine background. Here, we observed for the first time an indication for enhancements of 198Pt/195Pt isotope ratios in two diamond residues prepared by different chemical separation techniques from the Allende meteorite. Variations in other isotopic ratios were within analytical uncertainty, and no anomaly was identified in a third diamond fraction. © 2012, Elsevier B.V.