Date of Award


Document Type


Degree Name

Doctor of Philosophy (PhD)



Committee Member

Kenneth Marcus, Committee Chair

Committee Member

Brian Powell

Committee Member

George Chumanov

Committee Member

Carlos Garcia


The integration of the liquid sampling – atmospheric pressure glow discharge (LS-APGD) with Orbitrap mass spectrometers has led to a potential paradigm shift in the field of high certainty isotope ratio measurements. Since the dawn of the atomic age, mass spectrometry has played a critical role in performing isotope ratio measurements of uranium (U), plutonium (Pu) and other radionuclides. Traditionally, these measurements have been made using thermal ionization mass spectrometry (TIMS) instruments and, more recently, inductively coupled plasma mass spectrometry (ICP-MS) instruments. While the ability of these instruments to perform isotope ratio measurements with a high degree of certainty has been proven, they remain large laboratory-based instruments with long sampling times, especially those associated with TIMS. To this end, Clemson University and Pacific Northwest National Laboratory have interfaced the LS-APGD with Orbitrap mass spectrometers with the goal of developing a field deployable system capable of performing isotope ratio measurements that meet the International Target Values (ITVs) for Measurement Uncertainties in Safeguarding Nuclear Materials for U samples. The LS-APGD offers a number of attractive operating parameters for a field deployable source, including gas flow rates of 200 – 1000 mL min-1, liquid flow rates of 5-60 μL min-1 and power consumption of <50 W, all while operating in a total consumption mode with power densities >10 W mm-3. While the initial demonstration of LS-APGD ion source was completed using Orbitrap mass spectrometers, trap type mass analyzers have been largely ignored in the field of isotope ratio mass spectrometry. As such, this research involves two large unknowns in the field of isotope ratio mass spectrometry. Over the course of the research presented here, the LS-APGD-Orbitrap system has been used to measure a number of different certified reference materials (CRM) ranging in enrichment from natural to 80% 235U, and has been able to meet the ITV value for each of the sample types analyzed. Ultimately the system was able to measure CRM U-800 (assayed as 235U/238U = 4.265622) as 4.266922, with a combined standard uncertainty, (uc), of 0.040%. Given these results, the LS-APGD-Orbitrap system shows excellent promise in the fields of nuclear forensics and nuclear safeguards where high certainty measurements are required.



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