[Ifeffit] Basic questions about the preliminary data processing in Athena

[Haifeng Li]

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 <ragordon at 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
>
>
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