Collected k-space and fitting range
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 ? Kind regardsTerry
Hi Terry,
The only possible difference would be due to differences in background subtraction. In practice, it’s a good idea to collect data ~1 inverse angstrom above the range you will analyze to make sure the background behaves properly toward the top of the fitted range. But beyond that it shouldn’t make much difference.
—Scott Calvin
Sarah Lawrence College
On Mar 3, 2016, at 8:33 PM, Taehoon Kim
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. HTH, B -- Bruce Ravel ------------------------------------ bravel@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/
participants (3)
-
Bruce Ravel -
Scott Calvin -
Taehoon Kim