C.UK
Subject: Re: [ccp4bb] Questions about diffraction
For a full answer to all your questions, I refer you to the classic
textbook of M. M. Woolfson "an introduction to x-ray crystallography" by
Cambridge University Press. This book has been quite helpful to me of
late. Unlike some s
For a full answer to all your questions, I refer you to the classic
textbook of M. M. Woolfson "an introduction to x-ray crystallography" by
Cambridge University Press. This book has been quite helpful to me of
late. Unlike some similar texts I find it easy to read. There are even
examples!
> Something for you to chew on: how is it that the electrons of the protein,
> which are presumably not in phase with each other nor in exactly the same
> place in their orbitals from unit cell to unit cell (maybe they are?) when
> they scatter the photons, they result in interference? What are the
The "Bragg planes" are a contrivance of our invention to make the
math simpler and allow us to converse in shorthand terms like "Bragg's
Law". The photon's wave function interacts with the wave functions
of every electron it overlaps with, which is many unit cells because
our photons have quit
Would it be taking it too far to suggest that one could go all the way
and consider that each electron diffracts not as groups in a plane but
as individual electrons and a photon impinging on an electron with with
a specific phase will be diffracted in a specific direction. However the
lattice arra
Without resorting to a circular argument? You are asking too much.
However, this probability distribution is perfectly described by
considering a component wave model wherein coherence of the component
waves correlates with peaks in the probability distribution--i.e.
Bragg's Law.
IANAM (I am
Here's a fun way to think of it:
A photon hits a crystal and will diffract off in a certain direction
with the same energy as the original photon. The direction is subject to
a probability distribution based on the lattice, with angles at the
diffraction conditions being most likely and the br
Michel Fodje wrote:
For every direction where there is destructive interference and a
loss of energy there is a direction where there is constructive
interference that piles up energy. If you integrate over all directions
energy is conserved.
For the total integrated energy to be conserved, en
On Fri, 24 Aug 2007 14:40:13 -0600
Michel Fodje <[EMAIL PROTECTED]> wrote:
The mathematics works but doesn't necessarily mean the current
interpretation of the mathematics has any resemblance to what actually
happens in reality.
Sure, it does. Crystallography is traditionally
>For the total integrated energy to be conserved, energy will have to be
>created in certain directions to compensate for the loss in other
>directions. So in a direction in which the condition is met, the total
>will have to be more than the sum of the waves in that direction.
>How about consider
> You are just using the coherent fraction of the beam.
My point is that Braggs' law as currently understood does not preclude
the diffraction from waves which were non-coherent before hitting the
sample
> It is not clear at all how you arrive to that condition. By definition, if
> two waves are n
> For every direction where there is destructive interference and a
> loss of energy there is a direction where there is constructive
> interference that piles up energy. If you integrate over all
directions
> energy is conserved.
For the total integrated energy to be conserved, energy will have
> > 1. In every description of Braggs' law I've seen, the in-coming waves
> > have to be in phase. Why is that? Given that the sources used for
> > diffraction studies are mostly non-coherent.
>
> Think of Bragg's Law as explaining what happens to a single photon
> that is probabilistically scatte
Michel Fodje wrote:
Dear Crystallographers,
Here are a few paradoxes about diffraction I would like to get some
answers about:
...
3. What happens to the photon energy when waves destructively interfere
as mentioned in the text books. Doesn't 'destructive interference'
appear to violate the f
On Friday 24 August 2007 12:22, Michel Fodje wrote:
> 1. In every description of Braggs' law I've seen, the in-coming waves
> have to be in phase. Why is that? Given that the sources used for
> diffraction studies are mostly non-coherent.
Think of Bragg's Law as explaining what happens to a singl
Dear Crystallographers,
Here are a few paradoxes about diffraction I would like to get some
answers about:
1. In every description of Braggs' law I've seen, the in-coming waves
have to be in phase. Why is that? Given that the sources used for
diffraction studies are mostly non-coherent.
2. Trying
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