Production of a continuously tunable neutron beam free of higher-order contamination

A neutron velocity selector specifically designed as a higher-order neutron filter has been developed and tested. For wavelengths longer than 2.37 Å the device transmits more than 80% of the fundamental wavelength (λ) neutrons, while the rejection ratio for higher-order wavelengths (λn) is greater than 104. Together with a Cu2MnAl single-crystal monochromator, a continuously tunable polarized neutron beam that is free from higher-order neutrons can be produced for wavelengths between 2.37 and 4 Å, bridging the gap between a pyrolitic graphite filter and a Beryllium filter.