## 3 Results & Discussion
### Analysis of Anode  
XPS results for eight point scans on the anode--five on the cathode-facing side, A1-A5, and three on the opposite side, A6-A8--are shown in Figure 5. The location of each point scan is indicated in the diagram included as Figure 5a, and the two columns of spectra in Figure 5b are as described above for the glass envelope. Arbitrary vertical shifts were applied to improve readability. The eight point scans can be separated into three groups: A1, A2, and A3 are all located on discolored rings discernible on the cathode-facing anode surface (Figure 2). A4 and A5 are also on the cathode-facing side of the anode, but away from discolored rings. A6, A7, and A8 are distributed across the back of the anode, which directly face the glass envelope. Peak binding energies, background-deducted counts, S/N ratios, spectral lines, and species identification for each position can be found in tables located in the Appendix A. Species related to five elements were observed on the anode: Al, Ba, Ca, Mo, and W. Mo, the primary component of the anode, was observed at all points except A2 and A3. This indicates that deposits in these regions are \(>\)10 nm thick and correspond to the discolored rings. Ca signal was observed for points A2 and A3, but were extremely weak or absent at all other points. Al is present only as Al\({}_{2}\)O\({}_{3}\), and only at A1-A3 (in the discolored rings). As Ca is not present at A1, the presence of Al could suggest that the Al and Ca do not originate from the same sources, or that the materials were deposited at different times. Ba-containing compounds (BaO or BaCO\({}_{3}\)) are detected everywhere, but are particularly strong at points A1-A3. W was also detected, but only at points A4-A8 that are either on the back of the anode, or well away from the deposition rings facing the cathodes. Figure 4: S/N ratios for each relevant peak presented in Figure 3. For elements correlated to multiple peaks, the peak with the greatest height is included. For each position, the top bar is composed of elements found in the impregnate (Ca, Al, Ba, and Sc) and the bottom bar comprises elements found in the glass substrate (K, SiO\({}_{2}\), and MgO). Sc and Sc\({}_{2}\)O\({}_{3}\) binding energies are similar to those of Mo (within 2 eV of each other at \(\sim\)400 eV). Signal corresponding to energies of \(\sim\)400 eV only appear far away from the cathode (A4-A5), or on the back of the anode (A6-A8). At these locations signals from other impregnate elements are absent or trace. In contrast, at locations where other impregnate elements yield strong signals, the signal at \(\sim\)400 eV is absent. As Sc desorbed from the cathode would be expected to be present on the side of anode facing the cathode and strongest near the cathode or where other impregnate materials is found, we conclude that observed signals \(\sim\)400 eV arise from Mo. Figure 6 is a comparison of XPS results for the anode. For each peak labeled in Figure 5, the S/N ratio (included in the Appendix A) is plotted for each evaluated position. Similar to the case for the envelope, there are again contrasts in the observed signal position-to-position. Positions near the pinhole directly opposite the cathodes (A1-A3) shown signal from elements originating in the impregnate, while signal in the other positions (A4-A8) are correlated to elements that are primary components of the substrate. Figure 7a is a photograph of the cathode assembly before removal of the cathodes but after removal of the anode plate. The cathode housings (blue ring in \"zoom in\" image) are visible through  
Figure 5: (a) A diagram of the anode samples: the left portion of the diagram shows the anode surface facing the cathodes; the right shows the outward-facing surface. Each examined point is plotted, A1–A8. (b) On the left, the full XPS survey of each point scan with the three highest-intensity peaks identified. An arbitrary vertical shift is applied to A1, A3, A4, A6, and A7 to improve readability.