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Analytical methods to enhance detection of anthropogenic radionuclides in environmental matrices




Rosenberg, Brett L., author
Brandl, Alexander, advisor
Borch, Thomas, committee member
Henry, Charles, committee member
Pinder, John, committee member
Steinhauser, Georg, committee member

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The efficacy of methods that are used to detect radionuclides is dependent on the properties of the radionuclides and the matrices being analyzed. Gamma spectroscopy is an excellent tool for detecting very low quantities of a short-lived gamma-emitting radionuclide. However, as the probability of gamma ray emission decreases and the half-life increases, greater quantities of a radionuclide are required for detection by gamma spectroscopy. Since most transuranic actinides are usually not present in such quantities or concentrations in the environment, mass spectrometry is the preferred tool. For tritium, 90Sr, and other lower-Z elements that emit no easily detectable gamma rays, liquid scintillation counting is commonly used to measure the beta particles they emit. However, this methodology requires radiochemical extraction procedures to ensure a maximized ratio between signal and background. Nondestructive gamma spectroscopy was used to evaluate radiocesium content in soil and vegetation samples collected from the Fukushima prefecture exclusion zone in 2013 and 2014. Liquid scintillation counting was used for quantifying 3H in samples collected in 2013 and 90Sr in samples collected in 2013 and 2014. The radiocesium and 90Sr activities were found to have decreased from 2013 to 2014. Although 3H activities could be quantified in most samples, a sample from Chimeiji had a specific activity that statistically exceeded background (1.2 ± 1.6 Bq mL-1); further investigation is required to ascertain if 3H is present within that sample. Reports generated by TEPCO were also evaluated; radiocesium ratios and 131I/132Te ratios calculated from the reports reveal the importance of considering counting statistics and spectroscopic interference when drawing conclusions about the presence of anthropogenic radionuclides in environmental samples. Gamma spectroscopy was then applied to explore radiochemical separation techniques that can enhance detection of anthropogenic radionuclides, especially gamma-emitting actinides like 239Np shortly after a nuclear event. Ion specific extraction chromatography was found to be effective at minimizing spectroscopic interference from fission products, and addition of stable iodide carrier and a precipitating agent facilitated decreasing radioiodine activity within environmental samples. Extraction chromatography was found to reduce 131I interference by at least one order of magnitude, making it preferred for reducing 131I activity within an environmental sample. Extraction chromatography also avoids the potential of precipitating any analyte. The separation and measurement techniques utilized herein have effectively enhanced the ability to detect low-activity anthropogenic radionuclides; supplemental measurements gathered from the exclusion zone confirm the observed trends and prove the necessity of minimizing interference.


2016 Summer.
Includes bibliographical references.

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