Biology Reference
In-Depth Information
201
To add the amplitudes of the diffracted beams from these two electrons in
the phase plane vectorially, we need to calculate the phase difference from
the path difference by multiplying with where is the wave length of
the X-ray. Thus, if the amplitude of the diffracted beam from electron A is
denoted by then that from electron B is exp in the
direction of
s
.
The X-ray film then can be used to determine the reciprocal
space coordinates defined as:
Just like the physical space coordinates defined by
x
= (x,y,z), we also have
and
If we represent the specimen as electron density distribution, over its
volume, the total amplitude of the diffracted beams from all its electrons can
be calculated by the following integration:
where the triple integral indicates integration over the entire volume of the
specimen.
For uniformed electron density distribution along a right-handed helix, since
x and y are expressed in terms of z, the triple integral can be reduced to a
single integral. Also replace and by:
and
