Hi, Robert, Thanks for your help.
One more question. What is the real difference between calibration and alignment? Do they have specific meaning? Thanks, Haifeng On Sun, Jul 22, 2018 at 5:45 PM, Robert Gordon <ragor...@alumni.sfu.ca> wrote: > Hi Haifeng, > > Here's my take on what you described: > > Two sample to be studied at the same edge using the same reference. Three > scans on A and three on > B are done with simultaneous reference. > > First: compare the three reference scans for A. If they agree, then > compare the data scans. If they also look > similar (i.e. no evidence of changing in the beam), you can merge the > three data scans > on A right away. If the references don't agree, then you determine by how > much they differ (how much a correction > would be needed to bring them into alignment) and apply that same > correction to the data before merging. > It is not meaningful to merge data that is not aligned. (If the sample > scans show changes from scans 1 to 3, > then you need to rethink how to do the measurements) > > Repeat for B. > > Now compare the merged (corrected beforehand if necessary) references for > A and B. If they agree, > you can compare data for A and B (merged) directly. If they do not, > determine how much one reference > differs from the other and apply that same correction to, say, B, that > brings its reference into alignment with > A's reference, and then compare A and B > > You align the references between samples to the same value in order to do > a meaningful comparison > between them. If you report energy positions of features in your near-edge > spectra, the reader > would need to know to what energy those positions are referenced. > > When possible, I recommend references that have tabulated edge values > (i.e. metal foils). A reference > need not be the same edge as the one being studied. For arsenic, as an > example, the gold L3-edge is > quite close to the As K-edge and serves as a good reference. If not > possible to use a metal foil, use a > reference that another interested researcher could readily obtain or has > used. This allows for > comparison of reproducibility. If your reference looks nothing like > literature, you may have a problem > with the beamline or in how you processed the data. This should be one of > the first things you > check when you start taking data at the beamlne. > > You should also note how the beamline was calibrated when you did the > measurements. > > regards, > Robert > > > On 2018-07-22 1:21 PM, Haifeng Li wrote: > > Dear ALL, > > I am a beginner in Athena. Recently I got the spectra and I am confusing > about the data calibration and alignment. The manual shows that calibrate > the reference data of one scan and align other reference data to that > calibrated one. > > Here I want to show examples. I have two samples A and B, Each sample has > three scans with the corresponding reference data. For sample A, 1st scan > is calibrated and the other two scans are aligned to 1st scan. Then merge > them into merged A. The same procedures for sample B and get merged B. If I > want to compare XANES of sample A and B, do I need to align the merged > reference data between A and B? If so, why? My understanding is that all > scans (original data and merged data) in sample A and B are calibrated to > standard edge energy. Why do they need to align? > > I appreciate your help. > > Thanks, > > Haifeng > > > _______________________________________________ > Ifeffit mailing > listifef...@millenia.cars.aps.anl.govhttp://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit > Unsubscribe: http://millenia.cars.aps.anl.gov/mailman/options/ifeffit > > > > _______________________________________________ > Ifeffit mailing list > Ifeffit@millenia.cars.aps.anl.gov > http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit > Unsubscribe: http://millenia.cars.aps.anl.gov/mailman/options/ifeffit > >
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