I forgot to add in my original message that I believe figure 11 of appendix 3 further demonstrates that the magnitude of the species 69 signal seen in the spectra in figures 7 and 8 is not the direct byproduct of the sputter-cleaning process, because it does not show a similar post-sputtering 69 peak.
-Bob > -----Original Message----- > From: Robert Ellefson > Sent: Monday, October 13, 2014 11:37 AM > > Looking closely at figures 5-8 of appendix 3 of the Lugano report, I believe > we can see evidence for the evolution of a mass 69 species during > sputter-cleaning of the samples while undergoing ToF-SIMS analysis in a > scanning electron microscope. > > Figure 5 provides what amounts to a control run for these observations, with > only a carbon sticker present. The mass 69 peak in the spectrum is barely > visible, way down in the noise. My rough estimate from zoomed-in analysis > of the printed graph gives a count of ~530, or 5.3E+2. > > Figure 6 shows the mass spectrum for raw fuel grains before > sputter-cleaning, and the mass 69 peak is still way down in the noise, > although in the graph the count is approximately 6.0E+3 - somewhat higher, > but most notably, the 69 peak is a small fraction of the Ni-60 and Ni-58 > peaks. > > Figure 7 shows the mass spectrum for the same raw fuel grains following 180 > seconds of sputter-cleaning. Besides the absence of (presumed) siloxane > peaks, there is now a robust mass 69 peak, ~3.0E+4, which is nearly equal in > magnitude to the mass 60 peak. I believe that this peak indicates evolution > of the mass 69 in-situ during sputter-cleaning, likely as an intermediate > product in the nickel-lithium cyclic reaction which is driving the observed > enrichment processes. > > Following an additional 16 hours of inactive storage in the SEM vacuum > chamber, figure 8 shows the same sample material now has the siloxane > signature apparent once again, but the mass 69 signal is appearing with the > same relative abundance as the mass 60 peak. > > I do not have any direct experience with SEM analysis methods, and I am not > entirely certain what the significance of the ion source enrichment in Ga-69 > implies. However, I have a difficult time reconciling this series of graphs > with the notion that this peak-69 is occurring as purely instrument > artifact, owing to the great variability in abundance. > > In addition, I highly suspect that peak 23 represents a reactant, despite > the warnings from the report text that this could be an artifact. Once > again, I am hoping for further clarification from experts in ToF-SIMS > analysis to help clarify these interpretations. > > -Bob Ellefson >
