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

[Bruce Ravel]

On 07/27/2018 01:32 PM, Haifeng Li wrote:
> What is the real difference between calibration and alignment? Do they 
> have specific meaning?


In Athena, calibration means to determine a value for e0 shift such that 
a particular point in the data is specified to be a particular energy. 
Then the value for E0 is set to that particular energy.  Thus, 
calibration changes both e0 and e0 shift for the group being calibrated.

For example, set the E0 shift such that the first inflection point in 
copper is made to be 8979 eV.  Then set the value for E0 in the 
background removal to 8979.

In Athena alignment is the process by which one data group is given an 
e0 shift value such that it lines up with another data group.  This is 
to compensate for some scan-to-scan variability in the behavior of the 
monochromator.  Often, but not always, alignment is done using a 
zero-valent (or some other) reference which is measured simultaneously 
with the actual sample.  In Athena, the alignment tool DOES NOT change 
the value of e0, but certainly does change the value of e0 shift for the 
group being aligned.  The alignment tool does not change either e0 or e0 
shift for the alignment standard.

Whether you want to do one, the other, both, or neither depends upon the 
beamline and the type of data ensemble you have measured.

This /is/ explained in the user manual.

B


-- 
  Bruce Ravel  ------------------------------------ bravel at bnl.gov

  National Institute of Standards and Technology
  Synchrotron Science Group at NSLS-II
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