Is it really preferred orientation problem?

Dear all,

I was making a Rietvled analysis of a neutron powder diffraction patters from intermetallic compound LaNi4.25Al0.75.

If not using preferred orientation correction, the agreement indices are a little higher than those when using it.

Like Rp, Rwp, Chi2, RB are respectively from 3.96, 5.33, 2.68, 5.80

to 3.35, 4.42, 1.85, 3.07.

Their patters are:

But at the end of the file *.sum, there's such a sentence appears:

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=> WARNING!:
Are you really dealing with a preferred orientation problem?

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I am not sure of it, hope to hear some adivce.

If it is, for modifed March's function, the values of parameters are: Pref1=0.63353, Pref2=0.91337.

In accordance with the manual of FullProf, the powders are needle-like habit. It means the shape of

powders are like needle or other sth? And what's the meaning of the fibber axis direction?

By the way, I haven't known how to calulate the site radius so far. I have read the other two papers

following the suggestion of Dr Alan Hewat, but these two papers didn't tell the calculation course in

details. Is there some programs which can calculate it?

Thanks in advance.

-----------
Zhijian Fan

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