Actinide isotope ratios measured by Resonance Ionization Mass Spectrometry: optimization of ionization schemes and demonstration using nuclear fallout
Brewster, Drake E.
Smith, Craig F.
Isselhardt, Brett H.
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Resonance Ionization Mass Spectrometry is a technology for analysis of isotopic composition of samples that was developed as early as the 1980s. Since its development, technological advancements have enabled instruments such as the Laser Ionization of Neutrals instrument at Lawrence Livermore National Laboratory to deliver high yield isotope ratios with an accuracy within 1% at high measurement efficiency while remaining relatively free of isobaric interferences. The instrument has recently been successfully used to quantify uranium isotope ratios in nuclear fallout debris. The work in this thesis explored three pathways necessary for the development of a field deployable instrument. The first pathway addressed was a feasibility study that showed current continuous wave laser technology incompatible with the ionization approach taken in the current Laser Ionization of Neutrals instrument. Next, new one- and two-color uranium resonance ionization schemes were tested that showed an increase in uranium signal by 62% by accessing a low-lying excited state. The final experimental investigation studied the effects of carbon coating and implantation on nuclear fallout samples, showing a factor of two increase in the signal-to-noise ratio achieved during measurement of uranium isotope ratios.
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