Measuring Higher Order Neutron-Silicon Structure Factors with Pendellösung Interferometry Using a Pulsed Beam*

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 pendellösung, can be 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 neutron-silicon structure factors, which may be used to investigate interactions Beyond the Standard Model, measure the internal structure of the neutron via the neutron charge radius, and provide information on thermal motion of the atoms in a lattice. While neutron-silicon structure factors have recently been measured for the (111), (220), and (400) reflections, quality data do not yet exist for the case of high-order reflections. Progress towards using the pulsed beam at the VULCAN beamline located at the Spallation Neutron Source run by Oak Ridge National Lab to measure the (333), (444), and (555) reflections simultaneously will be discussed. Leveraging the pulsed beam to measure multiple structure factors simultaneously will reduce some of the systematic uncertainties associated with the previous experiment. A successful measurement will allow for the study of anharmonic contributions, increase the precision of the determined neutron charge radius, and provide further constraints on an atomic length scale "fifth" force.