Metal capillaries for neutron lenses

The use of metal reflective surfaces should greatly improve the transimission of neutron focusing devices based on glass polycapillary lenses because the longer scattering lengths of many metals allow greater critical angles compared to glass. The neutron transmission of single channel metal capillaries has been studied using cold neutron beams and an imaging neutron detector. Metal capillaries obtained from commercial sources have been studied both as supplied and as treated by chemical flow or electropolishing techniques to compare the transmission performance as a function of the smoothness of the metal surface. The reflectivities calculated from the experimental transmissions vary as a function of internal diameter and of capillary length, but are not sensitive to the various surface treatments studied here. None of the metal capillaries have reflectivities as good as the glass capillaries currently being used.