Re: A few questions

Ian Madsen ( ian.madsen@minerals.csiro.au )
Fri, 22 May 1998 08:51:18 +1000

At 18:41 21/05/98 +0100, you wrote:
>Dear Jens:
> here are some answers:
>
>1) you should not refine an absorption correction for Debye-Sherrer data, as
>it is too correlated with Debye-Waller factors. If you have an absorbing
>sample, you should calculate the absorption correction. You need to know
>the value of mu*R, where mu is the linear absorption coeeficient, and R is
>the radius of the cyclinder. When you have that, you can find the
>corrections in the International Table for Crystallography (volume C, I
>believe) and apply it to your raw data. For very strong absorbers you may
>need to run a Monte Carlo type program. There is also a simplifyed formula
>for weak absorbers, which is implemented in GSAS. You should not attempt to
>refine the value, though.

*** ------snip snip ------ ***

In addition to the above, you must remember to take into account the fact
that, for powder samples, the capillary sample you pack will not have a
perfect packing density (PD). The formula above should become mu * R * PD.
For the 0.3 and 0.5 mm diameter capillaries we use, the packing density is
typically 0.35 to 0.4. It is possible to measure the PD by weighing the
capillary before and after packing and measuring the length of sample in
the tube + tube diameter (a graduated microscope/telescope is usefull here).

Cheers

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Ian Madsen
CSIRO Minerals
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