Browsing by Author "Buczak, K"

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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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    New exotic and non-standard radionuclides in AMS
    (GNS Science, 2011-03-21) Wallner, A; Buczak, K; Plompen, A; Schumann, D; Semkova, V
    Isobaric interference represents one of the major limitations in mass spectrometry. In the very few cases in AMS where nature allows isobaric-free measurements, lowest background levels are accessible. Such conditions are given, if the isobar does not form stable negative ions either as atomic ion, or by choosing a suitable molecular species; well-known examples are e.g. 14C−, 26Al−, 129I−, or 41CaH3 −, respectively, and also for the unstable isotopes in the mass range above Bi. In this work, we will present a few additional cases where isobaric interference is completely excluded, among them 55Fe, 68Ge and 202Pb. Applications will be discussed where the exceptional sensitivity of AMS offers important insights to such different fields like nuclear astrophysics, nuclear physics and general physics issues. VERA, a dedicated AMS facility, based on a 3-MV tandem, featuring high mass resolution in combination with efficient background suppression and an automated measurement procedure, allows to transport all nuclides from hydrogen to the actinides through the system up to the detector stations. Such a facility is well suited for developing the tuning and measurement procedures for new and non-standard isotopes. We will demonstrate the actual measurement limits of such radionuclides for the VERA facility and results for selected applications. In order to generate final values AMS usually relies on the parallel measurement of reference materials. We will discuss the production of such materials for these non-standard AMS nuclides.Copyright (c) 2011 AMS12.
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    A novel approach for neutron-capture studies of 235U and 238U
    (GNS Science, 2011-03-25) Wallner, A; Belgya, T; Bichler, M; Buczak, K; Dillmann, I; Käppeler, F; Mengoni, A; Quinto, F; Steier, P; Szentmiklósi, L
    Improved and highly accurate nuclear data are urgently required for the design of advanced reactor concepts. This demand holds for minor actinides but also for the main fuel materials. Existing data were measured by detection of the prompt capture γ-rays. A major difficulty in these experiments is the safe discrimination against the strong γ-background from the competing fission channel. Recent studies exhibit critical discrepancies at keV energies for both, 235U(n,γ) and 238U(n,γ) with great impact on the keff-value of fission reactors. Neutron activation with subsequent accelerator mass spectrometry (AMS) measurement of the reaction product represents an independent technique, where interference from fission is completely excluded. Within the European EFNUDAT project, new measurements were performed with the goal to determine the neutron capture cross sections of 235U and 238U via neutron irradiations at thermal (cold) and keV energies: Activations were performed with cold neutrons (Budapest Research Reactor), thermal (Atominstitut, Vienna) and with neutrons of 25 and 450 keV (Karlsruhe Institute of Technology). The produced long-lived 236U and the decay product of 239U, 239Pu were subsequently counted by AMS at the Vienna Environmental Research Accelerator (VERA). This method for measuring the neutron capture cross section has the advantages that the involved systematic uncertainties are in no way correlated with those inherent to previous techniques. Therefore, this experiment provides important and independent information for these key reactions of reactor physics with uncertainties expected below 5%. The high sensitivity of AMS requires only very small samples. New results for 235U(n,γ)236U and 238U(n,γ)239U in the energy range from thermal to 500 keV will be presented. The challenges of measuring 236U/238U isotope ratios at the 10-12 level and to quantify 239Pu with high precision will be highlighted. Finally, the potential for extending that method to other isotopes in that mass range will be discussed. Copyright (c) 2011 AMS12