[Ifeffit] Multiple Domains in Athena

[Matt Newville]

Michael,

On Sun, Nov 20, 2016 at 5:41 AM, Karl-Michael Schindler <
karl-michael.schindler at physik.uni-halle.de> wrote:

> Hi.
>
> I would appreciate hints about how to treat multiple domains in Athena.
> The simplest system would be one with only twofold rotational symmetry, but
> present in two domains rotated by 90°. Somehow equivalent to the case of
> unpolarized x-rays.
>
> I am fairly new to using Athena and i may have simply missed the answer in
> the documentation.
>
> Michael.
>

X-ray absorption averages over the atoms in the volume illuminated by the
beam.   As the beam is attenuated by the sample, fewer X-rays make it to
portions of that volume at depth.

If you have multiple local structures in your sample, the XAFS signal is a
simple average of those local structures, weighted by the probability that
an atom with a particular structure absorbs an X-ray. For a uniform sample
with a mixture of sites, that weighting is the simply the fraction of atoms
with each structure.   If the sample is not uniform, it can be more
complicated.  In particular, heterogeneity that is a function of depth
(say, a layered material) is more complicated, because atoms near the
surface are more likely to absorb the X-ray than samples at depth.

Hope that helps,

--Matt
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://millenia.cars.aps.anl.gov/pipermail/ifeffit/attachments/20161120/893af86c/attachment.html>