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HI Haifeng,<br>
<br>
Suppose you measure Fe foil three times, and all three scans
overlap. They are aligned.<br>
But suppose the edge positions are at 7116 eV instead of 7112 eV.
The calibration is off.<br>
You can adjust to it, but, as Carlo mentioned, it is really an angle
correction, not simply a<br>
shift in energy. It is better to have an accurate calibration to
begin with, then aligned and<br>
calibrated would be the same.<br>
<br>
Note: Choice of target calibration can differ - some use the X-ray
data booklet values<br>
<a class="moz-txt-link-freetext" href="http://xdb.lbl.gov/">http://xdb.lbl.gov/</a><br>
and some use the Kraft et al. values<br>
<a class="moz-txt-link-freetext" href="https://aip.scitation.org/doi/abs/10.1063/1.1146657">https://aip.scitation.org/doi/abs/10.1063/1.1146657</a><br>
<br>
Just state which calibration you are using when
presenting/publishing.<br>
<br>
-R.<br>
<br>
<br>
<div class="moz-cite-prefix">On 2018-07-27 10:32 AM, Haifeng Li
wrote:<br>
</div>
<blockquote type="cite"
cite="mid:CAGLYwKPG+GXJNuSkDjoQSoMD_g+o9MmoHkkNy5r9mkaAJ5L+qw@mail.gmail.com">
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<div dir="ltr">
<div>Hi, Robert, <br>
</div>
<div><br>
</div>
<div>Thanks for your help. <br>
</div>
<div><br>
</div>
<div>One more question. What is the real difference between
calibration and alignment? Do they have specific meaning? <br>
</div>
<div><br>
</div>
<div>Thanks, <br>
</div>
<div><br>
</div>
<div>Haifeng <br>
</div>
</div>
<div class="gmail_extra"><br>
<div class="gmail_quote">On Sun, Jul 22, 2018 at 5:45 PM, Robert
Gordon <span dir="ltr"><<a
href="mailto:ragordon@alumni.sfu.ca" target="_blank"
moz-do-not-send="true">ragordon@alumni.sfu.ca</a>></span>
wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0
.8ex;border-left:1px #ccc solid;padding-left:1ex">
<div text="#000000" bgcolor="#FFFFFF"> Hi Haifeng,<br>
<br>
Here's my take on what you described:<br>
<br>
Two sample to be studied at the same edge using the same
reference. Three scans on A and three on<br>
B are done with simultaneous reference.<br>
<br>
First: compare the three reference scans for A. If they
agree, then compare the data scans. If they also look<br>
similar (i.e. no evidence of changing in the beam), you
can merge the three data scans <br>
on A right away. If the references don't agree, then you
determine by how much they differ (how much a correction<br>
would be needed to bring them into alignment) and apply
that same correction to the data before merging.<br>
It is not meaningful to merge data that is not aligned.
(If the sample scans show changes from scans 1 to 3,<br>
then you need to rethink how to do the measurements)<br>
<br>
Repeat for B. <br>
<br>
Now compare the merged (corrected beforehand if necessary)
references for A and B. If they agree,<br>
you can compare data for A and B (merged) directly. If
they do not, determine how much one reference<br>
differs from the other and apply that same correction to,
say, B, that brings its reference into alignment with <br>
A's reference, and then compare A and B<br>
<br>
You align the references between samples to the same value
in order to do a meaningful comparison<br>
between them. If you report energy positions of features
in your near-edge spectra, the reader<br>
would need to know to what energy those positions are
referenced.<br>
<br>
When possible, I recommend references that have tabulated
edge values (i.e. metal foils). A reference<br>
need not be the same edge as the one being studied. For
arsenic, as an example, the gold L3-edge is <br>
quite close to the As K-edge and serves as a good
reference. If not possible to use a metal foil, use a<br>
reference that another interested researcher could readily
obtain or has used. This allows for <br>
comparison of reproducibility. If your reference looks
nothing like literature, you may have a problem<br>
with the beamline or in how you processed the data. This
should be one of the first things you<br>
check when you start taking data at the beamlne.<br>
<br>
You should also note how the beamline was calibrated when
you did the measurements.<br>
<br>
regards,<br>
Robert
<div>
<div class="h5"><br>
<br>
<div class="m_5169180293350795761moz-cite-prefix">On
2018-07-22 1:21 PM, Haifeng Li wrote:<br>
</div>
</div>
</div>
<blockquote type="cite">
<div>
<div class="h5">
<div dir="ltr">
<div>Dear ALL, <br>
</div>
<div><br>
</div>
<div>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. <br>
</div>
<div><br>
</div>
<div>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?</div>
<div><br>
</div>
<div>I appreciate your help. <br>
</div>
<div><br>
</div>
<div>Thanks, <br>
</div>
<div><br>
</div>
<div>Haifeng <br>
</div>
</div>
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