The sample shows definite Mg, Sr, S, Cl, Rh (from the tool), Ar, K, Ca, Fe, and what appears to be Yb at 7.4kev. Scanning with no filter, Helium flushing, 15kV, 35microA. Raw photon counts seem elevated without reason (52-55k). This sample does not show other trace spikes which could include Co or Ni.
Hi
Can you show a spectrum?
Count rate is moderately high... Have you checked if this peak is an escape peak ( other intense peak reduced by 1.74keV) or a pile-up peak of other intense lines?
It's not any peak that goes with an element, that's the problem. There shouldn't be anything there but noise, so it should match the rest of the end curve for no-filter, but there is a definite hill at 7.71kev, that's what gets me. When I get to work tomorrow I can post a pic and a spectra file to match. When using this tool we're seeing this little peak on almost all the no-filter spectra for this core, and a few others. On the green filter spectra we see the parts of the gun, like Rh, so I was almost thinking that some Yb was in the gun, but we weren't informed. But that one lump at 7.71 gets me. I've looked through the line records for Berkeley, Harvard, the Bruker documentation, and a few other labs that posted reports of updates to Berkeley's book from 2009, and nobody has a listing for that index. I'm hoping our gun isn't fubar.
Completing the comments of Philipp Hoenicke, another possibility is a diffraction peak. This can occur when some minerals are oriented in the sample (e.g, very common for calcite) and Bragg's Law is satisfied. These peaks disappear or shifts in the spectra when the specimen rotated. Will be nice to see the full spectra.
example of diffraction peak in XRF: http://www.edax.com/periodic-table/chromium-xrf.aspx
I've added a spectra file to the top of this question (PDZ format - zipped because this page thinks pdz is an image format).
If it's a diffraction peak, wouldn't it go away if I moved the rock around or switched samples every 60 seconds, as we're doing? It continues to be there through multiple feet of core scanning, and always on the "standard" sample we use to check for shifting.
One of the things we're noticing is that if Mg values change, the Yb and adjacent hump reacts opposite the change in Mg. We're aiming for a raw photon output of 30-40k, but when we have this interaction, we're seeing raw data in the 52-55k range. Without fail, the Mg, Yb, and the raw count seem to go hand in hand with this core, and our standard sample. Our gun can't properly read Mg, so I wonder if it has to do with that?
Last night I was starting to think our calibration was off, and that we'd shifted our copper to the left, so I ran a brass sieve today to determine if copper was in the right place, and it is, as is iron. This only confirms for me that this can't be nickel or cobalt at this location.
Granted this is a tiny amount of something, but it seems to mean something, and I'd like to understand what that might be.
Thanks for the help so far. Learning is good!
To add another component to the problem: I understand that your sample is a rock sample. If the Yb is from the sample, it seems very weird to me that there should be no no other Lanthanoides. Maybe this is also something different.
I wondered about that too, and was thinking it might be part of the gun. It only really appears when doing Helium flushed scans with no filter. It seems odd that every inch of this sample, for maybe 100 feet, should register Yb and this little magic hump with no name.
I managed now to look at the spectrum. I am pretty sure that the lines at 7.4 and 7.7 are sum peaks. Ca is the strongest contribution to your spectrum, so there is some probability that you register two photons at once. So from 3.69+3.69 you get roughly 7.4 and from 3.69+4.01 you get 7.71.
You can easily check that if you change the distance of the Tracer IV-SD to the sample a little bit. If you choose a distance such that the Ca peak is reduced to about 50% intensity, the sum peaks lose intensity to only 25% (probability is squared).
Thank you, I will try this and see what happens. Another question comes up though. Why does it only happen on this core and our standard rock? Of the ten cores we've finished, it isn't visible in other carbonates. We always use our tracer directly touching the rock, as directed from Bruker.
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