On the impulse approximation in electron Compton scattering

Electronic structure measurement via Compton scattering requires the impulse approximation to be satisfied. This states that the inelastic collision time is short, so that the ‘secondary’ electron ejected out of the atom is effectively free of the crystal potential. The robustness of the impulse approximation is tested for boron nitride and aluminium using momentum-resolved electron energy loss spectroscopy. Reliable (with respect to impulse approximation) electronic structure information is obtained for Compton peak energies at ∼250 eV energy loss or higher. These experimental results are validated using a simple Kronig-Penney model of the secondary electron travelling through the crystal. For loosely bound valence electrons the impulse approximation is satisfied when the Compton peak energy is significantly larger than the mean inner potential of the crystal. This criterion provides a straightforward estimate of the experimental conditions required for extracting reliable Compton data from any given material.