Coherent Elastic Scattering

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:
graphite coherent

The mathematical express of the energy-angle distribution and integrated cross section for coherent elastic scattering is as follows:

coherent elastic

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.


23 January 2013 T-2 Nuclear Information Service