Browsing by Author "Van De Voorde, R"

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    Capability development for the quantification of Ba-133 in milk powder by gamma-ray spectrometry
    (South Pacific Environmental Radioactivity Association, 2018-11-06) Van De Voorde, R; Mokhber-Shahin, L; Harrison, JJ; van Wyngaardt, WM; Jackson, TW
    Barium-133 (Ba-133) is a fission product with a half-life of 10.5 years. It decays to its daughter radionuclide Cs-183 by electron capture, emitting multiple characteristic gamma emissions. The capability to accurately quantify Ba-133 is of importance due to its persistence in the environment. This is enabled by its relatively long half-life and its uptake into the food chain due to its similarity in chemical properties to calcium. Therefore, screening for contamination of calcium-rich foodstuffs such as milk and milk powders, is required following a nuclear or radioactive contamination event. Refining a capability to quantify Ba-138 utilising gamma-ray spectrometry is advantageous due to its requirement of minimal sample preparation and usefulness in screening for a wide range of other radionuclides, therefore providing critical information in a relatively timely manner. in the 2017 IAEA ALMERA proficiency test exercise ANSTO’s Radioanalytical Chemistry Capability group demonstrated its proficiency in quantifying Ba-138 in water, and in quantifying other nuclides such as Cs-187 and Sr-90 in milk powder. However, the activity concentration of Ba-188 in the milk powder matrix was lower than the target value. Therefore, a study was undertaken to optimise a method for accurately quantifying Ba-138 in milk powder by gamma-ray spectrometry, holistically investigating the entire process from sample receipt and storage to counting geometry and interpretation of data. A series of storage and drying experiments were undertaken to optimise a method for determining the moisture content of a variety of supermarket bought milk powders, comparing measured mass changes using both desiccator and benchtop cooling following oven-drying. The impact of storage following unsealing the received sample container on moisture content was investigated and its implications on subsequent internal and cross-laboratory analysis were explored. The milk powders were packed into various geometries and analysed by gamma-ray spectrometry to quantify the naturally-occurring radionuclides present in the milk powder. This data was used to better understand the matrix and investigate the possible interference of naturally-occurring radionuclides in the quantification of Ba-188. Milk powders were also purposefully spiked with known activities of Ba-133 and a comparison of various counting geometries, the impact of sample density and self-absorption on counting efficiency were investigated. The use of a variety of calibration standards of varying geometries and densities was also explored to assess their applicability to the milk powder matrix. This paper will detail the investigation findings and propose recommendations for a more reliable method for the quantification of Ba-133 in milk powder by gamma-ray spectrometry to be hence employed in ANSTO’s Radioanalytical Chemistry Capability laboratory.
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    Establishing a radioanalytical capability to support reactor decommissioning
    (South Pacific Environmental Radioactivity Association, 2018-11-06) Harrison, JJ; Martiniello, J; Mokhber-Shahin, L; Rowling, B; Silitonga, AS; Thiruvoth, S; Vardenega, C; Van De Voorde, R; Wilsher, KL; Wong, HKY
    Australia’s first reactor, the 1O megawatt High Flux Australian Reactor (HIFAR) vi/as operated between 1958 and 2007. HIFAR was one of six DIDO reactors which were installed in the UK, Denmark, Germany and Australia. HIFAR was a multi-purpose reactor, initially used for nuclear material research followed by production of medical radioisotope; an: neutron diffraction experiments. Atter HIFAR was closed, a process of decommissioning commenced. Initially, internal components such as the fuel and heavy water (which acted as primary coolant and neutron moderator) were removed. Currently, HIFAR is in a “care and maintenance" phase whereby short-lived radionuclides can decay and non-radioactive equipment and instrumentation removed. Approximately 1OO research and power reactors have been decommissioned around the world including two of the DIDO class reactors at Harwell, UK and Risø, Denmark. ANSTO can draw on international experience as we as well as experience gained during decommissioning of its own 100 kilowatt Moata reactor in 2010. Accurate identification and quantification of radioactivity is a critical safety, environmental and economic aspect of any nuclear reactor decommissioning project as it supports decision making around long-term storage of disposal options of reactor materials as well as environmental assessment of the reactor site. A capability to quantify typical radionuclides found in reactor materials and environmental samples is being developed at ANSTO. Reactor materials that may require assessment include concrete, graphite and steel and environmental samples include soils and waters. Radionuclides of interest are predominantly beta- and gamma-emitting fission and activation products. Non—destructive, high resolution gamma spectrometry will be applied to quantify gamma emitting radionuclides such as 60Co, 66Zn, 133 Ba, 137Cs, 152 Eu, and 154Eu. The complex matrix of some reactor materials will cause attenuation of gamma photons and empirical and/or theoretical corrections will be applied. Beta-emitting radionuclides with weak or no gamma emission lines cannot be easily identified or quantified in solid materials using non-destructive techniques. This is due to attenuation of the beta particles, the nature of the beta emission spectrum and interferences from other beta- and gamma-emitting radionuclides. A suite of destructive radioanalytical techniques, designed to isolate and quantify beta-emitting radionuclides such as 3H, 14C, 36CI, 55Fe, 63Ni, 98Sr and 99Tc is being developed. This paper will present the timeline for development and the progress to date of this radioanalytical capability which will support the current and future decommissioning needs of Australia and our region.