[Ifeffit] Large Amplitude Values

Gavin Garside gavin_garside at yahoo.com
Sat Jul 31 10:56:18 CDT 2010


Thank you for a quick response.  The value I am getting for SO2 in the fit most 
of interest is 2.95 plus/minus 3.72.  So with the error bar I am in range, but I 
was just suspicious of it before I make any claims about it.  All my experiments 
were done in florescence because we have ordered bulk material.  By creating a 
sample that would work in fluorescence I may have introduced dislocations or 
imperfections that would have effected the physical properties of interest in 
this sample. 

Gavin Garside
University of Utah

From: Scott Calvin <SCalvin at slc.edu>
To: XAFS Analysis using Ifeffit <ifeffit at millenia.cars.aps.anl.gov>
Sent: Sat, July 31, 2010 4:52:35 AM
Subject: Re: [Ifeffit] Large Amplitude Values

Hi Gavin,

What are the uncertainties on the high S02 values? 

Fluorescence is unlikely to be the culprit. While it can affect your ability to 
normalize properly, you're unlikely to account for a factor of 2 by 
normalization if the data is relatively decent. And self-absorption tends to 
suppress S02, not exaggerate it.

Why did you switch to fluorescence on just the handful of data sets? That might 
provide us a clue.

--Scott Calvin
Sarah Lawrence College

On Jul 30, 2010, at 10:47 PM, Gavin Garside wrote:

Fellow X-Ray Absorption Enthusiasts,
>I have recently compiled a model that gives excellent visual fits in R, q, and k 
>space for bond spacing in a BCC structure.  This model gives bond spacings that 
>make sense, and are very close to what would be expected from this set.  The R 
>factors are very low, and the enot values correspond quite well to the edge.  
>However, our amplitude values are much larger than typically expected.  They 
>come in at the range of 1.8 up to 5.0, but only on a few data sets.  On all the 
>rest the amplitude values are 0.4 to 1.0.  Could this increase in amplitude be 
>attributed to the fact that we ran florescence measurements instead of 
>transmission, and have a weaker signal coming to the detector?  What else could 
>be causing this in only one data set? All samples used in this model have the 
>same structure.  Thanks in advance to any replies, your help and time is 

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