[Ifeffit] Collected k-space and fitting range

Bruce Ravel bravel at bnl.gov
Fri Mar 4 08:40:23 CST 2016

On 03/03/2016 08:33 PM, Taehoon Kim wrote:
> Hello,
> I am a bit confused about the range of k-space, which may affect the
> quality of EXAFS fitting.
> I would like to understand whether there is a difference between the
> fitting using an identical fitting range of k-space obtained from
> different range of k-space collected.
> For example, is there a notable difference between a fitting of k =
> 2.3-11 which was deduced from a spectra data collected up to k=12 and a
> spectra data collected up to k=13 ?

The fit is made over the specified k-range and /does not/ consider the 
data outside the k-range.  It's really that simple.

It happens often that we collect data over a larger range than we choose 
to analyze.  It can be hard to tell before making a measurement at what 
point the statistical or systematic noise in the measurement will become 
bigger than the signal. As Scott suggests, we typically measure over a 
somewhat large data range then restrict the analysis to a more 
conservative range in order to exclude the part of the data for which 
the signal is swamped by the noise.

It is for that reason that Athena provides you with separate controls 
for the k-range of the background removal and of the Fourier transform.


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

  National Institute of Standards and Technology
  Synchrotron Science Group at NSLS-II
  Building 535A
  Upton NY, 11973

  Homepage:    http://bruceravel.github.io/home/
  Software:    https://github.com/bruceravel
  Demeter:     http://bruceravel.github.io/demeter/

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