
In crystalline materials consisting of coherent scatterers
(e.g., graphite, beryllium, beryllium oxide), the
scattering from different planes of atoms can interfere,
leading to a series of "Bragg edges" as the neutron wavelength
hits various possible atomic spacings. The thermal elastic
cross section of graphite is shown below:
The mathematical express of the energyangle distribution
and integrated cross section for coherent elastic scattering
is as follows:
Note that the scattering distribution is completely defined
by the the energy locations and sizes of the steps in the
integrated cross section. The GROUPR module and the MCNP
Monte Carlo code take advantage of this feature.
