Simulation of Neutron Phase Imaging

Hi, everyone
I recently got involved in neutron grating imaging. The neutron grating imaging works on the same principle as X-ray.I want to do same simulation work with Geant4. But Geant4 does not involve the physical processes of neutron diffraction and refraction. Is there anyone who has done the similar work, or know how to add the diffraction and refraction process of neutron in Geant4.