Using the Neutron Fizeau Effect and Neutron Interferometry to Measure Energy-Dependent Contributions to the Neutron Optical Potential

TL;DR

This work targets the energy dependence of the slow-neutron optical potential, $dV_{opt}/dE$, by leveraging the neutron Fizeau effect in moving matter and high-sensitivity neutron interferometry. The approach isolates the energy-dependent piece of the forward-scattering amplitude, enabling a direct, precise mapping of $dV_{opt}/dE$ across near-threshold energies. A detailed treatment of subthreshold and near-threshold resonances within the neutron-optical framework is developed, including special handling of $s$-wave levels near $E=0$ and negative-energy resonances, with applications to parity violation in low-energy $p$-wave resonances and to neutron scattering in rare-earth nuclei. The proposed method promises enhanced nuclear data quality and provides a platform for probing fundamental interactions via resonance phenomena, with practical feasibility at existing facilities and pulsed neutron sources.

Abstract

We propose a method to measure the energy dependence of the neutron optical potential $dV_{opt}/dE$ in the slow neutron energy regime. Our method makes essential use of a special property of the phase shift for a nonrelativistic neutron in moving matter, known as the neutron Fizeau effect. If a neutron traverses a medium which moves along the surfaces of its own parallel boundaries, the neutron only experiences a phase shift if the neutron optical potential of matter depends on the incident neutron energy. This feature of the neutron Fizeau effect can be combined with newly-developed forms of neutron interferometry to conduct sensitive measurements of $dV_{opt}/dE$. We describe some examples of scientific applications of this idea in the fields of neutron optics, subthreshold neutron-nucleus resonances, parity violation in low-energy p-wave neutron-nucleus resonances, and neutron scattering amplitudes of the nuclei of rare earth elements.