Dear Blaise,
A chi^2 of 500 means that on average your model is off by 500 sigma, or
500*500=250000 counts. This usually means some technical detail has gone
wrong in file formats or weights.
If you don't manage to figure out the problem then if you can post your
refinement somewhere I am sure someone reading the list will be able to
help (should only need original data file in a phillips format,
converted file in gsas format, and your .exp and instrument parameter
file).
Best,
Jon
Mibeck, Blaise wrote:
I am re-learning GSAS to bring Rietveld to my department (for the first
time). We have an old Phillips Xpert.
I am trying to refine a quartz standard to acquire my profile and
instrument parameters for this instrument and have yet to get my Chi^2
below 500. The instrument is not in my direct control. I have caught and
asked them to correct a few problems already (dwell time too low,
aluminum sneaking into the beam, etc…) and this has helped. I would like
not to annoy them any more than I have too.
At this point I think my high Chi^2s are mainly due to low angle
asymmetric peaks that my fit is not able to copy – the asym is not
terrible but may be messing me up. I am getting better results with peak
profile functions 3 and 4, but unable to get Chi^2 below 500. My scans
go up to 70 degrees 2theta.
I would like to tell the people caring for the instrument that my
problem is on their end, but I am not confident in my own refining
skills to say this. When I work with the tutorials or standard data from
my graduate school experiment I am ok – I think I am proceeding in a
reasonable way, although I can get stuck here and there.
I would like to find out if I am doing something incorrectly or if the
problem is instrument related. I hate to bug one of you but wonder if I
could get someone to look at my work?? Is there a better forum for
asking for this kind of help?
Kindest regards to all of you,
Blaise
* * * * * * * * * * * * *
Blaise Mibeck
Research Scientist
Energy & Environmental Research Center
University of North Dakota
15 North 23rd Street, Stop 9018
Grand Forks, ND 58202-9018
Phone: (701) 777-5077
Email: [EMAIL PROTECTED] <mailto:[EMAIL PROTECTED]>
