Doctoral Dissertations

Date of Award

5-2017

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Nuclear Engineering

Major Professor

Howard L. Hall

Committee Members

Lawrence H. Heilbronn, Steven E. Skutnik, Michael J. Sepaniak

Abstract

The precise and accurate determination of isotopic composition in nuclear forensic samples is vital for assessing origin, intended use and process history. Thermal ionization mass spectrometry (TIMS) is widely accepted as the gold standard for high performance isotopic measurements and has long served as the workhorse in the isotopic ratio determination of nuclear materials. Nuclear forensic and safeguard specialists have relied heavily on such methods for both routine and atypical efforts. Despite widespread use, TIMS methods for the assay of actinide systems continue to be hindered by poor ionization efficiency, often less than tenths of a percent; the majority of a sample is not measured. This represents a growing challenge in addressing next-generation nuclear detection needs by limiting the ability to analyze ultra-trace quantities of high priority elements that could potentially provide critical nuclear forensic signatures. Porous ion emitter (PIE) thermal ion sources were developed in response to the growing need for new TIMS ion source technologies. By simultaneously incorporating multiple, previously developed strategies for improved ionization efficiency, PIEs have proven to be simple to implement, straightforward approach to boosting ion yield.

This work serves to expand the use of PIE techniques for the analysis of trace quantities of plutonium and americium. PIEs exhibited superior plutonium and americium ion yields when compared to direct filament loading and the resin bead technique, one of the most efficient methods for actinide analysis, at similar mass loading levels. Initial attempts at altering PIE composition for the analysis of plutonium proved to enhance sample utilization even further. Preliminary investigations of the instrumental fractionation behavior of plutonium and uranium analyzed via PIE methods were conducted. Data collected during these initial trial indicate that PIEs fractionate in a consistent, reproducible manner; a necessity for high precision isotope ratio measurements. Ultimately, PIEs methods were applied for the age determination of various uranium isotopic standards. PIEs did not exhibit significant advantages for the determination of model ages when compared to traditional filaments; however, this trial was able to provide valuable insight for guiding future investigations.

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