diffraction pattern

Jim Pflugrath jwp at RigakuMSC.com
Wed Aug 28 09:13:04 EST 2002


Let me try an analogy.

Consider a reciprocal lattice point to be a basketball or golf ball (for
Wulf B.) in or near a layer of oil that floats on the surface of a smooth
ocean of water.  A reflection would be X-rays that run from the center of
the earth through the parts of the ball in oil and hit your detector.

Only the portion of the ball that intersects the oil gives rise to
diffraction that you see on your image.  The parts of the ball above the
oil are not seen; neither are the parts of the ball below the oil.

If the layer of oil is thicker than the ball, then the reflection is a
full reflection.  That is, the entire ball is within the oil.

If the ball is thicker than the layer of oil, then only the parts of the
ball in oil are imaged on the detector.  That is, you have partial
reflection.  In order to image the unseen parts of the ball, you have to
do something.  One thing you can do is push the ball through the oil, so a
different section of the ball is imaged as you push it through.  A crystal
might be rotated to push reciprocal lattice points (basketballs) through
the oil layer (surface of the Ewald sphere).  You can add up the sections
or parts that are imaged to get a full reflection.  You could make the oil
layer thicker, too; that's a Laue experiment.

I'd say both full reflections and partial reflections are real
reflections.


On Tue, 27 Aug 2002, Aida Baharuddin wrote:

> hi,
>
> I have 1 simple basic question. Actually, what is real reflections and
> partial reflections which
> are being differentiated by different colours in  DENZO. Could anyone
> out there explain to me
> the theory.
>
> thanks
> Aida Baharuddin





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