Precision neutron-interferometric measurement of the coherent neutron-scattering length in silicon

The neutron-interferometry (NI) technique provides a precise and direct way to measure the bound, coherent scattering lengths b of low-energy neutrons in solids, liquids, or gases. The potential accuracy of NI to measure b has not been fully realized in past experiments, due to systematic sources of error. We have used a method which eliminates two of the main sources of error to measure the scattering length of silicon with a relative standard uncertainty of 0.005%. The resulting value, b=4.1507(2) fm, is in agreement with the current accepted value, but has an uncertainty five times smaller. [S1050-2947(98)04808-2].