[Ifeffit] Ifeffit Digest, Vol 67, Issue 12

Matt Newville newville at cars.uchicago.edu
Tue Sep 9 11:14:12 CDT 2008

Syed, Adam,

I think the suggestion from Adam and one of the suggestions from
Anatoly assume the energy linear in time.  Is that the really case?
For quick-scanning modes, many beamlines run the mono at a constant
angular velocity, so that time maps linearly to angle, which then
needs to be converted (non-linearly) to energy.  Then again, some
quick-scanning beamlines use a special cam drive, in which neither
angle nor energy would be linear in time.

Again, you need know these details in order to correctly assign
energies to the data.  None of it is particularly difficult, so
there's no point in guessing, and stretching or massaging the energy
scale until two energy points correct does not mean the rest are
correct.    You need to find out from the beamline how the data mapped
onto energy and fix that.   While you can probably use Ifeffit macros
within Athena to do this correction, this is really a job for the
beamline, not for Athena.  Having an option in Athena that allowed the
user to say "I don't know why my energy scale is bad, but can you
please stretch the energies so that these two energies are what I'd
like them to be" is a horrible idea.


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