Degree Type

Dissertation

Date of Award

1995

Degree Name

Doctor of Philosophy

Department

Mechanical Engineering

First Advisor

Jerry Lee Hall

Second Advisor

Edward Jaselskis

Abstract

There are approximately 1800 uncontrollable hazardous waste sites across the United States. The Department of Energy (DOE) is responsible for cleaning up several of these sites that were contaminated as a result of producing weapon-grade nuclear fuels in different states since the 1940s. Site characterization is the first and a very critical step in the remediation program of a radioactive contaminated site. During this process, all the necessary information about location, level, and chemical composition of the contaminated sites must be collected for the clean up planning. Ames Laboratory, one of the U.S. Department of Energy sites, has adopted and developed the Laser Ablation-Inductively Coupled-Atomic Emission Spectrometry/Mass Spectrometry (LA-ICP-AES/MS) techniques to build a robotic field-deployable analytical mobile lab for site characterization of the radio-active contaminated sites. The Robotic Surface Sampling Accessory (RSA) with its sampling probe and the mobile lab are a practical setup for a safe, fast, and inexpensive soil analysis without exposing the operators to the hazardous radio-active wastes;A high-power Q-switched Nd:YAG pulsed laser beam is used to ablate and generate very fine particles inside an ablation cell from the contaminated soil. The ablated particles are entrained in the argon gas flow inside the ablation cell and then transferred via a 100-foot Tygon tube to either the ICP-AES or the ICP-MS for final elemental analysis;The objectives of this work were to design, build, and test surface and subsurface ablation cells, as a part of the sampling probe, for soil sample collection using the Laser Ablation (LA) technique. First, different forces acting on the ablated particles due to their motion in the ablation cell and transfer line are identified and calculated. The movement of entrained particles inside the ablation cell and transfer line is mathematically modeled. Then, the flow behavior inside different Plexiglas cell models was studied. By considering the theoretical and experimental results, two final cell designs were selected for building the prototype ablation cells. Finally, the performance of the prototype cells were thoroughly investigated by running a series of tests using the ICP-AES, ICP-MS, Scanning Electronic Microscope (SEM), and image analysis;The flow deflector ring, which is a unique and important part of the surface ablation cell, had a significant effect on the output signal intensity of the ICP-MS. By using this ring the mixing characteristics of the surface ablation cell were improved. This effect enhanced the aerosol quality by increasing its homogeneity and the number of the small particles entrained in the aerosol. This increased the signal intensity of the ICP-MS by a factor of two for the surface ablation cell without changing the laser parameters. The flow deflector channel in the sub-surface ablation cell had a very similar effect on the output signal characteristic of this cell;Both cells had good mixing characteristics and the signal fluctuation due to the change in the aerosol density was minimum. The laser power loss due to the scattering of the laser beam by ablated particles was minimum. The percent of relative standard deviations (RSD%) of the output signal intensities of the ICP-AES for surface ablation cell 14% for the ICP-AES and 30% for the ICP-MS respectively.

DOI

https://doi.org/10.31274/rtd-180813-10166

Publisher

Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/

Copyright Owner

Reza Bashirzadeh

Language

en

Proquest ID

AAI9610939

File Format

application/pdf

File Size

139 pages

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