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08/13/2004: "Report Number Ten from NASA"

Maine Space Grant Consortium
NASA Internship Program
Dr. L.E. Nyquist, Thermal Ionization Mass Spectrometry
“Investigations of Chemical and Physical Processes on Hot Re Filaments in Relation to Ion Yield in Thermal Ionization Mass Spectrometry”
Report #10 (Week Ending 8/13/04)

   This week there is little of interest to report simply because new developments were not forthcoming as I finalized my data, charts, graphs, tables and the final report. On Monday I worked on some notes that I intended to use in a discussion with Dr. Nyquist regarding the conclusions that our work this summer have made possible. Dr. Nyquist had also given me a few relevant papers regarding the latest ideas we have had regarding the ionization process.
   On Tuesday I met at length with Dr. Nyquist to discuss my data, results, conjectures and ideas. He added a new wrinkle to our investigations when he suggested that chemical processes may not be dominant in the ionization process and that the physical process of evaporation could be considered to play a large role in determining the ‘effective activation energy’. On Wednesday I continued working on putting my data into a presentable form and corrected some errors. There was still one problem that I had not resolved and that was that the signal strengths I calculated based on the data we took were not even close to the actual signal strengths I observed. I went over every step in my calculations and could find no fault with any part of it. I asked Dr. Nyquist to look it over as well and he could find no fault with it either. This left me with the conviction that there must be an assumption somewhere that I was overlooking. I did not find out what this assumption was until Thursday morning.
(click on 'more' to read more)


   With Dr. Nyquist’s help I found that the trouble was that I was using average values when I should have been using the individual ‘effective activation energies’ instead. By calculating the expected signal strength for each element at temperatures consistent with the range of their highest signal strength using the averages I was producing numbers that no individual run would duplicate. The solution was to calculate expected signal strengths using the lowest and highest ‘effective activation energy’ values. This forced me to create two different tables to display the information but it will be more useful for all of that. The tables show the typical ‘best’ temperature range for ionization for each element and the strength of the signal that one can expect on a millivolt per nanogram basis. Also included are the vapor pressures of the elements at each extreme of the given temperature range. These data were included in order to illustrate the additional importance being given to each element’s tendency to evaporate in our model of the ionization process.
   We have always known that the ‘effective activation energy’ that we’ve been calculating this summer encompassed more processes than the simple loss of an electron required for ionization. This process, in isolation, is fairly well described by the idea of comparing the work function of the surface to the ionization potential of the sample element. When the ionization potential is less than the work function it costs more energy to remove an electron from the surface than to remove one from the sample element. When the ionization potential is larger than the work function it costs more energy to remove an electron from the sample element than to remove one from the surface. By comparing the difference in these two quantities (assuming that the work function is a constant, which it is not) to the empirical values for the ‘effective ionization energy we can find the energy that is in excess of simple ionization.
   This excess energy would encompass the heat required for evaporation and the conceivable chemical reactions that occur on the filament. One such reaction may be the oxidation of the filament surface, which plays a role in increasing its work function. This process does contribute to lowering the cost of ionization (as an isolated process) but in turn requires an input of energy.
Dr. Nyquist invited me out for lunch with some other employees at the lab on Thursday and I spent the rest of the day working on my report, etc.
   On Friday I finished the report around mid-day and gave it to Dr. Nyquist for his comments. He had already commented on the portion I had finished up to yesterday afternoon so there was not much left to for him to read. All the same, he had a more hectic day than he expected and will have to give me some comments on the report after I’ve left. We have spoken and decided that it would be a good idea to keep in touch and Dr. Nyquist invited me to consider coming back for another summer. It has been a good and successful research project and now I’m going to get ready for the drive home.