Browsing by Author "Zorko, B"

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    Actinides AMS for nuclear safeguards and related applications
    (Elsevier, 2010-04) Hotchkis, MAC; Child, DP; Zorko, B
    The nuclear safeguards system which is used to monitor compliance with the Nuclear Non-proliferation Treaty relies to a significant degree on the analysis of environmental samples. Undeclared nuclear activities can be detected through determination of the isotopic ratios of uranium and plutonium in such samples. It is necessary to be able to measure plutonium at the femtogram level in this application, and measure the full suite of uranium isotopes (233–238U) where the total uranium content may be at the nanogram level. In this paper we describe the development of our accelerator mass spectrometry system for such analyses, with particular reference to recent improvements in our methods. The commissioning of a fast isotope cycling system for actinides has led to improved precision, with reproducibility of 4% for actinide isotope ratios. The background level for the key rare isotope 236U is found to be 8.8 fg, for total uranium content in the nanogram range, and is limited by 236U contamination rather than ion mis-identification. For plutonium the background is at the low femtogram level. © 2009 Published by Elsevier B.V.
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    A fast switching electrostatic deflector system for actinide isotopic ratio measurements
    (Elsevier, 2010-04-01) Zorko, B; Child, DP; Hotchkis, MAC
    We have implemented a fast switching electrostatic system on the actinides beamline on the ANTARES accelerator at ANSTO, to improve the precision of analyses by accelerator mass spectrometry. This high-energy bouncing system is based on a pair of deflector plates, deflecting in the orbit plane, set at the entrance and exit of the analysing magnet. The design of deflector plates is unique, and it was modelled by SIMION in order to minimize field inhomogenity and fringe field effects. The pair of deflector plates are supplied by a high-voltage amplifier driven by an EPICS-enabled control unit, with two 4 W power supplies providing up to ±10 kV modulation. The high-energy bouncing system is synchronized with the existing low-energy bouncing system. To measure the isotopic ratio with the new system, the magnetic fields of the injector and analysing magnets are set to transmit selected isotopes along the beam line with zero voltage applied. The other isotopes of interest are transmitted by keeping the magnetic fields constant and modulating the voltages on the injector magnet chamber and on the high-energy deflector plates. © 2009 Elsevier B.V.
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    Ionisation efficiency improvements for AMS measurement of actinides
    (Elsevier, 2010-04) Child, DP; Hotchkis, MAC; Whittle, KR; Zorko, B
    Measurements of the isotopic ratios of plutonium and uranium are utilised by the safeguards community, environmental radioactivity and remediation studies, oceanography research, and in the U-series dating of geological samples. Accelerator Mass Spectrometry offers the advantages of high selectivity and sensitivity for such ratio measurements, but suffers from a poorer ionisation and transmission efficiency than some other mass spectrometric techniques. In addition, the ionisation efficiency achieved in caesium-sputter ion sources can be variable depending on the chemical form and geometry of the target used, yielding actinide negative ion beam rates with efficiencies ranging from 0.05% to 0.5%. In this paper we investigate the impact of the crystal structure of the target material, chemical composition and the geometry of the target in order to determine conditions which will allow us to maximise beam output and increase the efficiency of AMS measurements in future. We also examine target stability and “burn in time” (the time taken to generate a stable beam current) in conjunction with these measurements in order to maintain a high precision of measurement during the measurement period. © 2009 Published by Elsevier B.V.