Biology Reference
In-Depth Information
202
The final expression of the integral becomes:
However, since the helix has a pitch P, the Bragg's law of diffraction gives
constructive interference only on layer lines determined by
where is the angle between unit vectors
s
and
s
o
,
and n is an integer. In
the near forward direction, the layer lines are shown in Fig. 8-1, with
specific values of equal to:
for a being very small. The integration over the entire length of z can be
replace by from 0 to P. Together with a change of variable,
the total amplitude of the diffracted beam,
A(h)
, is proportional to:
