Development activities in the accerlerator operations group development task

The Operations Group Development team within the ANSTO Accelerator facilities are currently persuing a number of activities to further develop our equipment and technical capabilities. These include broadly; *Electron Cyclotron Resonance Ion Sources (ECRIS) * Virtual Instrumentation * Beam Profile Monitor Enhancements * Vacuum System Operation Methods * Current Digitisers/Integrator

Accumulation of plutonium in mammalian wildlife tissues: comparison of recent data with the ICRP distribution models

We examined the distribution of plutonium (Pu) in the tissues of mammalian wildlife to address the paucity of such data under environmental exposure conditions. Pu activity concentrations were measured in Macropus rufus (red kangaroo), Oryctolagus cuniculus (European rabbit), and Pseudomys hermannsburgensis (sandy inland mouse)inhabiting the relatively undisturbed, semi-arid conditions at the former Taranaki weapons test site at Maralinga, Australia. Of the absorbed Pu (distributed via circulatory and lymph systems) accumulation was foremost in bone (83% ±10% SD), followed by muscle (9% ±10%), liver (7% ±7%), kidneys (0.5% ±0.3%), and heart (0.4% ±0.4%). The bone values are higher than those reported in ICRP 19 and 48 (45-50% bone), while the liver values are lower than ICRP values (30-45% liver). The ICRP values were based on data dominated by relatively soluble forms of Pu, including prepared solutions and single-atom ions produced by decay following the volatilisation of uranium during nuclear detonation (fallout Pu, ICRP 1986). In contrast, the Maralinga data relates to low-soluble forms of Pu used in tests designed to simulate accidental release and dispersal. We measured Pu in lung, GI-tract and the skin and fur as distinct from the absorbed Pu in bone, liver, muscle, and kidneys. Compared with the mean absorbed activity concentrations, the results for lung tissues were higher by up to one order of magnitude, and those in the GI tract contents and the washed skin/fur were higher by more than two orders of magnitude. These elevated levels are consistent with the presence of low-soluble Pu, including particulate forms, which pass through, or adhere upon, certain organs, but are not readily absorbed into the bloodstream. This more transitory Pu can provide dose to the lung and GI tract organs, as well as provide potential transfer of contamination when consumed in predator-prey food chains, or during human foodstuff consumption. For example, activity concentrations in O. cuniculus edible samples prepared according to traditional aboriginal methods were more than two orders of magnitude higher than in muscle alone. The increase was due to inclusion of GI tract components and contents in the traditional method. Our results provide new insights into the sequestration of Pu in mammalian tissues under environmental exposure conditions. These results contrast with those related to the specific forms of Pu and exposure conditions upon which the ICRP models were based. However, they provide data relevant to the assessment of key environmental legacy waste sites, and of potential release scenarios for the low-soluble oxide forms in the growing worldwide inventory of Pu associated with power production

Choosing the right stripper gas from AMS and other applications with tandem accelerators at low and medium terminal voltage

Recent experimentation with stripper gases used for Accelerator Mass Spectrometry (AMS) has seen a divergence in the practices adopted at laboratories performing AMS of high mass species (such as actinides) at low and medium terminal voltages. At low voltages (<1 MV), the Ion Beam Group at ETH Zurich has demonstrated the advantages of using helium as the stripper gas, for both radiocarbon AMS [1] and for actinides AMS [2]. Meanwhile, at ANSTO we have investigated several gases at 4 MV [3, 4] and find that a multi–atom molecular gas such as sulphur hexafluoride provides the best yield for actinides AMS. In both cases, data published 40 years ago provided clues as to the optimum gas in each situation

Plutonium and uranium contamination in soils from the former nuclear

The British government performed a number of nuclear weapon tests on Australian territory from 1952 through to 1963 with the cooperation of the Australian government. Nine fission bombs were detonated in South Australia at Emu Field and Maralinga, and a further three fission weapons were detonated in the Monte Bello Islands off the coast of Western Australia. Analysis of neutron capture products and residual nuclear material from detonated nuclear weapons can allow information on the weapon used to be inferred. In addition a nuclear forensic examination of samples from well characterised sites such as these is an important exercise to develop techniques for detection of clandestine nuclear activities. A number of samples were collected by the Australian Radiation Laboratories in 1972 1978, 1983 and 1990 at the Monte Bello Islands, in 1977 from Emu field and in 1977 and 1984 at Maralinga as part of site management and cleanup activities to gauge residual radioactivity levels. To this end we have secured a number of soil samples from the ARL archives which had been collected from the Monte Island and Maralinga sites. These samples were originally analysed for gamma emitting fission products and in a few cases the residual weapon material, 239+240Pu, was analysed by alpha spectrometry. We have now analysed some of these soils for plutonium and uranium isotopic concentrations and also 240Pu:239Pu isotopic ratios using the ANTARES AMS facility, ANSTO. The neutron capture product 233U was also analysed as a test of capability to detect the presence of thorium fuel cycle activities in environmental matrices.Copyright (c) 2011 AMS1

Plutonium and uranium contamination in soils from former nuclear weapon test sites in Australia

The British government performed a number of nuclear weapon tests on Australian territory from 1952 through to 1963 with the cooperation of the Australian government. Nine fission bombs were detonated in South Australia at Emu Junction and Maralinga, and a further three fission weapons were detonated in the Monte Bello Islands off the coast of Western Australia. A number of soil samples were collected by the Australian Radiation Laboratories in 1972 and 1978 during field surveys at these nuclear weapon test sites. They were analysed by gamma spectrometry and, for a select few samples, by alpha spectrometry to measure the remaining activities of fission products, activation products and weapon materials. We have remeasured a number of these Montebello Islands and Emu Junction soil samples using the ANTARES AMS facility, ANSTO. These samples were analysed for plutonium and uranium isotopic ratios and isotopic concentrations. Very low Pu-240/Pu-239 ratios were measured at both sites (similar to 0.05 for Alpha Island and similar to 0.02 for Emu Field), substantially below global fallout averages. Well correlated but widely varying U-236 and plutonium concentrations were measured across both sites, but U-233 did not correlate with these other isotopes and instead showed correlation with distance from ground zero, indicating in situ production in the soils. © 2013, Elsevier Ltd

Use of multiply charged atomic ions for isotope ratio mass spectrometry.

We have investigated the use of multiply charged atomic ions for the measurement of isotopic ratios of gaseous and vapour samples. We use a mass spectrometer system incorporating an electron cyclotron resonance (ECR) ion source for this purpose. In the cases of carbon, nitrogen and oxygen, the selection of the 2+ atomic species is found to be the most effective for obtaining reliable isotopic ratios. Using samples of carbon dioxide, nitrogen, air and water vapour, we have demonstrated the determination of the isotopic ratios C-13/C-12, N-15/N-14, O-17/O-16 and O-18/O-16. For oxygen, this technique offers an alternative to the equilibration or purification methods normally required to obtain isotopic ratios of water or other oxygen-containing samples. In particular, O-17/O-16 can be measured directly without isobaric interference from OH+. With typical ionization efficiencies of greater than 10%, ECR ion sources have the potential to enable measurements on very small samples. In addition to those evaluated in the present work, there is scope for application of this method to other sample types, to a variety of sampling methods, and to other elements. © 2008, Wiley-Blackwell

Actinides AMS for nuclear safeguards and related applications.

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

Performance of an electron cyclotron resonance ion source designed for isotope ratio mass spectrometry.

We have designed, built, and tested an electron cyclotron resonance ion source suited to the needs of an experimental program examining new methods of isotope ratio mass spectrometry using multiply charged ions. Contaminant levels have been reduced to low levels. Sample absorption and desorption effects are under investigation and preliminary results are presented. © 2008, American Institute of Physic

High sensitivity analysis of plutonium isotopes in environmental samples using accelerator mass spectrometry (AMS).

This article presents a methodology for the determination of the concentration and isotopic ratio of plutonium occurring at femtogram levels in environmental matrices such as soils and sediments by accelerator mass spectrometry (AMS). Results on analyses of a number of reference materials ( IAEA-375, IAEA-135, IAEA-300, IAEA-327, NIST 4350, NIST 4353b) are presented as validation of the method in reproducibly measuring the plutonium isotopic ratio Pu-240 : Pu-239 in a variety of environmental sample matrices. © 2008, Royal Society of Chemistr

Fast switching electrostatic deflector system for actinide isotopic ratio measurements.

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