Doctoral Dissertations

Date of Award

12-1983

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Physics

Major Professor

Thomas A. Callcott

Abstract

We have designed and assembled a Resonance lonization Mass Spectrometry (RIMS) system which includes a NdrYAG laser microprobe, laser-induced multiphoton resonance ionization, a time-of-flight (TOP) mass spectrometer, and a novel data acquisition system. The laser microprobe allows the analysis of any solid sample with a minimum of sample preparation, and requires only a small amount of material (~100 μg per pulse). The ionization technique is based on Resonance lonization Spectroscopy (RIS). This method uses photons from a tuneable dye laser to resonantly excite atoms of a single element from the ground state to an intermediate state. The excited atoms are then ionized by other photons from the same dye laser pulse. Using RIS, one can selectively ionize atoms of one element in the presence of many other elements. The chemical selectivity of RIS coupled with mass analysis provides an effective technique for isotopic analysis without interference from other elements having isotopes of the same mass. The TOP mass spectrometer allows the measurement of each isotope for every pulse of the ionizing laser system. The data acquisition system digitizes each mass peak individually for computer analysis.

Here we have described the RIMS system in detail and have reviewed the theory of laser vaporization, RIS, TOP mass spectrometry, and also isotope shifts, since these were found to be important. Using the RIMS system, we have measured the relative population of ground levels and the velocity distribution for Sm atoms vaporized by the laser microprobe to determine the excitation and kinetic temperatures, respectively. The excitation temperature was slightly greater, and this is explained by reference to a theoretical model. The selectivity of the RIMS system is demonstrated by experiments with Cr in steel and with a Nd-Sm alloy. The importance of isotope shifts in isotope ratio measurements is shown for Nd and Sm.

Finally, we have discussed conclusions based on this work and have suggested future investigations and possible modifications to the current RIMS system.

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