Adding the X-ray Bragg reflection physical process in crystal to the Geant4 Monte Carlo simulation toolkit, part I: reflection from a crystal slab.

X-ray diffraction from a solid crystal shows the wave nature of photons. It is an important electromagnetic (EM) physics process when X-ray photons interact with a crystal. Bragg diffraction, often called Bragg reflection, is a special case of the general form of X-ray diffraction, known as Laue diffraction. When the Bragg's law is met, the incident photon beam is reflected from the crystal plane behaving as a specular reflection at the Bragg angle. However, the Bragg reflection physical process has not been integrated into the general-purpose Monte Carlo simulation toolkit Geant4 for particle physics. In the current study, we developed a new EM physical process class "G4CrystalBraggReflection" and a new EM physical model class "G4DarwinDynamicalModel" for modeling the Bragg reflection physical process within a crystal. We added the Bragg reflection physical process to the EM physics category of Geant4. The preliminary results of photon tracking in a silicon crystal slab have shown the feasibility of simulating the Bragg reflection process in addition to the standard EM processes in the framework of Geant4.