Collaborative Research: Neutron Interferometry Experiments in Nuclear Physics

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A neutron interferometer splits the wave function of a free neutron into two coherent beams by Bragg diffraction in a single silicon crystal. The relative phase shift caused by different path lengths, potentials, or materials in the beams produces interference fringes in one or more neutron counters. This phase can be measured within a fraction of a degree in an interferogram so the neutron interaction potential in the sample can be determined to high precision. This program is focused on using neutron interferometry to make precision neutron scattering length measurements of importance to nuclear physics. The neutron interferometer measures a phase shift so it has direct access to the scattering length. This is a fruitful and often more precise alternative to nuclear scattering experiments which measure a cross section (a product of scattering lengths). For example, in a cross section measurement one is limited by uncertainty of the incident neutron flux; in a phase shift measurement that is not important. Experiments include precision measurement of few body neutron scattering lengths, important for improving our understanding of the nucleon-nucleon potential through semi-phenomenological models and effective field theories; and a precision measurement of the neutron mean-squared charge radius, an important quantity for understanding the internal structure and dynamics of the neutron.According to the theory of quantum mechanics, all matter becomes wave-like when it moves very slowly. Matter waves exhibit wave properties such as diffraction and refraction that are normally associated with light waves. A neutron interferometer uses neutron matter-wave diffraction in a silicon crystal to split a slow neutron beam into two distinct paths. By placing a test sample into one of these paths, and observing the resulting wave interference, we can precisely measure the interaction of the neutron beam with the sample. Such measurements are used to improve our understanding of the physical forces between neutrons and matter, and of the fundamental sub-structure of matter itself.