Measuring Higher-Order Neutron-Silicon Structure Factors with Pendellösung Interferometry*

Dynamical diffraction gives rise to multiple waves inside perfect crystals when the incident wave nearly satisfies a Bragg scattering condition.  The interference of these waves, called Pendellosung, is observed by "fringe-like" modulation of the intensity of the transmitted or diffracted beams exiting the crystal. Pendellösung interferometry can be used to precisely determine the neutron-silicon structure factor. Structure factors for several different Bragg conditions provide strong constraints for interactions Beyond the Standard Model of particle physics, measure the internal structure of the neutron via the neutron charge radius, and provide information on thermal motion of the atoms in a lattice; aka the Debye-Waller factor.  Measuring higher-order structure factors allows for the study of anharmonic contributions, increases the precision of the determined neutron charge radius, and can provide further constraints on an atomic length scale "fifth" force.