At 07:05 PM 2/1/99 +0100, you wrote:
>
>
>Dear All,
>
>I have a diffraction profile which spans 5-160 degrees. My problem is
>getting an adequate fit for four or five peaks which lie in the range 7-20
>degrees. I have split my data into two histograms (5-20 and 20-160 deg) to
>try and alleviate the problem, and although the fit is better it remains
>imperfect. Unfortunately, the problem-peaks are the most important part of
>the data profile - I have an occupancy factor which is sensitive only to
>these peaks. I believe a peak-profile based on Pearson-VII rather than
>Pseudo-Voigt would resolve the problem. What I would like to know is:
>
I presume that you want to use Pearson VII to fit low angle profiles
as those peaks are assymetric. It sounds like you have significant axial
divergence. Have you tried Jephcoat,Finger, Cox modification to
Pseudo-voight (profile function 3 in GSAS)? It usually dose a very good job
of fitting axial divergence.
Another solution might be to use longer wavelength radiation and
push the critical peaks to higher angles where axial divergence will not be
as severe.
************************************************************************
Apurva Mehta
SSRL/SLAC
PO Box 4349, MS 69
Stanford, CA 94309
(650) 926 4791
(650) 926 4100 - FAX
************************************************************************
