Re: [sdpd] Re: how to purchase a high resolution diffractometer

[cockcroft...@gordon.cryst.bbk.ac.uk]

>> Both of our machines have primary beam monochromators - yes,
>> there is a loss of intensity, but I prefer the extra
>> "resolution" I get the higher angles due to the pure alpha1
>> wavelength.
>
>About the Kalpha-2 component, I have a different point of view.
>In order to explain it, I have installed some figures in a Web
>page entitled : "K-alpha : believe your eyes or trust mathematics ?".
>I don't think that you have any extra resolution at the higher
>angles. This is only an illusion, and you should not trust your
>eyes, you have to trust physics and mathematics.
>
>          http://www.cristal.org/powdif/kalpha.html

I prefer to believe my eyes (given that the 3 ifs mentioned in your
web page are not satisfied in my experience) - afterall that is why
ones uses obs & calc plots and not just R-factors :-)))

I should also point out that what I meant by higher angles
might more strictly be-calleded intermediate angles, i.e. those where
the alpha1,2 peak splitting is present but not resolved. Some of the
peaks at these sort of angles may be required for indexing and the human
eye can be very good (with practice) at distinguishing single from multiple
peaks, but less so when two wavelengths are present and all the peaks are
multiple by definition.

So I beg to differ with you Armel on this point ....

I do agree with you that if one collects alpha1,2 data, then that is the data
one should fit, but that is another story...

Jeremy Karl Cockcroft.

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